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In bioengineering, scaffold proteins have been increasingly used to recruit molecules to parts of a cell, or to enhance the efficacy of biosynthetic or signalling pathways. For example, scaffolds can be used to make weak or non-immunogenic small molecules immunogenic by attaching them to the scaffold, in this role called carrier. Here, we present the dodecin from Mycobacterium tuberculosis (mtDod) as a new scaffold protein. MtDod is a homododecameric complex of spherical shape, high stability and robust assembly, which allows the attachment of cargo at its surface. We show that mtDod, either directly loaded with cargo or equipped with domains for non-covalent and covalent loading of cargo, can be produced recombinantly in high quantity and quality in Escherichia coli. Fusions of mtDod with proteins of up to four times the size of mtDod, e.g. with monomeric superfolder green fluorescent protein creating a 437 kDa large dodecamer, were successfully purified, showing mtDod’s ability to function as recruitment hub. Further, mtDod equipped with SYNZIP and SpyCatcher domains for post-translational recruitment of cargo was prepared of which the mtDod/SpyCatcher system proved to be particularly useful. In a case study, we finally show that mtDod-peptide fusions allow producing antibodies against human heat shock proteins and the C-terminus of heat shock cognate 70 interacting protein (CHIP).
Translational riboswitches are cis-acting RNA regulators that modulate the expression of genes during translation initiation. Their mechanism is considered as an RNA-only gene-regulatory system inducing a ligand-dependent shift of the population of functional ON- and OFF-states. The interaction of riboswitches with the translation machinery remained unexplored. For the adenine-sensing riboswitch from Vibrio vulnificus we show that ligand binding alone is not sufficient for switching to a translational ON-state but the interaction of the riboswitch with the 30S ribosome is indispensable. Only the synergy of binding of adenine and of 30S ribosome, in particular protein rS1, induces complete opening of the translation initiation region. Our investigation thus unravels the intricate dynamic network involving RNA regulator, ligand inducer and ribosome protein modulator during translation initiation.
The Corona pandemic has painfully taught us the threat of new pathogens in a globalized world and how vital modern vaccines are. Platform technologies play an important role in the discovery of new vaccines as reducing the time for the development dramatically — time that saves lives. Here, we present the protein Dodecin and how it may be utilized as a versatile platform technology to produce cheap and robust new vaccines for everyone in all parts of the world.
Um sich an ändernde Umwelteinflüsse und metabolische Bedürfnisse anpassen zu können, ist es für Zellen essenziell, dass Boten-RNA (engl. messenger RNA, mRNA) stetig und schnell nach der Translation abgebaut wird. In Prokaryoten ist dafür der Proteinkomplex Degradosom verantwortlich, in dem Endo- und Exoribonukleasen RNase E und PNPase das RNA-Transkript in kleinere Fragmente und schließlich einzelne Nukleotide spalten. Die DEAD-Box Helikase RhlB im Komplex dient zusätzlich dazu, mögliche Sekundärstrukturen in der RNA zu entfalten, welche sonst die weitere Degradation behindern würden. Es konnte gezeigt werden, dass RhlB’s sehr geringe katalytische Aktivität – gemessen durch ATP-Verbrauch und Rate an entwundener RNA – signifikant durch die allosterische Bindung an Komplexpartner RNase E erhöht wird. Gleichzeitig deuten andere Studien darauf hin, dass RhlB eine mögliche Selektivität für doppelsträngige RNA-Substrate mit 5‘-Einzelstrang-Überhängen aufweist.
Diese Arbeit liefert neue Erkenntnisse in Bezug auf die Kommunikation zwischen den Degradosom-Komponenten RhlB und RNase E aus E. coli, indem das potenzielle Wechselspiel zwischen RhlBs RNA-Selektivität und der allosterischen Aktivierung durch RNase E untersucht wurde. Der vielseitige Einsatz NMR-spektroskopischer Techniken sowie die Verwendung kurzer RNA-Substrate mit spezifischen Strang-Eigenschaften ermöglicht es, mit einen ungewöhnlichen, RNA-zentrierten Ansatz an diese unzureichend verstandene Protein-Interaktion heranzugehen.
Zunächst wurden hierzu eine Reihe kurzer doppelsträngiger RNA-Konstrukte hergestellt, die sich nicht nur in ihren Einzelstrang-Merkmalen unterscheiden, sondern auch die thermodynamischen Anforderungen eines DEAD-Box Helikase Substrats erfüllen, und gleichzeitig eine ausreichende NMR-spektroskopische Signal-Zuordnung erlauben. Die thermale Stabilität, das Faltungsverhalten sowie die 1H Imino-protonen- und 13C HSQC-Zuordnungen aller geeigneten Konstrukte wurden erfolgreich bestimmt.
Um den Einfluss spezifischer RNA-Substrate sowie die Bindung zweier verschiedener RNase E Fragmente auf RhlBs ATP-Umsatzrate zu untersuchen, wurde sich zunächst eines photometrischen Phosphat-Assays bedient. Damit konnte deutlich gezeigt werden, dass RhlB in Abwesenheit des Komplex-Partners nicht in der Lage ist, signifikante Mengen an ATP umzusetzen, unabhängig davon, welches RNA-Konstrukt eingesetzt wird. Die Bindung der RNase E Fragmente erhöhte signifikant die ATP-Hydrolyse-Rate der Helikase, wobei die größte Aktivierung für den RNA-Duplex mit 5‘-Einzelstrang sowie ein einzelsträngiges Substrat zu beobachten ist. Da diese Ergebnisse deutlich eine RNA-Abhängigkeit beim ATP-Umsatz der Helikase zeigen, wurde untersucht, ob diese Unterschiede ihren Ursprung bereits in der Bindung der spezifischen RNA-Substrate haben. Mittels einer Mischapparatur, die es erlaubt die enzymatische Reaktion direkt im Spektrometer zu initiieren sowie zeitaufgelöster 31P NMR-Experimente konnte die allosterische Aktivierung der ATP-Hydrolyse-Rate von RhlB auch unter NMR-spektroskopischen Messbedingungen nachgewiesen werden.
Da die Ergebnisse des ATPase Assays deutlich eine RNA-Abhängigkeit bei der ATP-Umsatz-Rate der Helikase zeigen, wurde zusätzlich untersucht, ob diese Unterschiede ihren Ursprung in den Affinitäten für die verschiedenen RNA-Substrate haben und ob diese durch die Bindung von RNase E and RhlB beeinflusst werden. Um im gleichen Zuge zu überprüfen, ob die Bindung der RNA an RhlB die RNA-Konformation oder Basenpaarung ändert, werden 1H NMR-Titrationsexperimente durchgeführt. Es konnte erstmals gezeigt werden, dass RhlB eine inhärente Präferenz für Duplexe mit 5‘-Überhang gegenüber Konstrukten mit 3‘-Überhang oder stumpfen Enden besitzt, was sich in einer erhöhten Affinität zeigt. Zusätzlich offenbaren die Messungen, dass RNase Es allosterische Bindung selektiv die Affinität gegenüber Konstrukten mit Einzelstrang-Überhang erhöht, während die Affinität zu RNA Duplexen ohne Überhang sogar verringert wird. Diese Ergebnisse liefern erstmals einen Nachweis, dass RNase E aktiv Einfluss auf RhlBs RNA-Bindung nimmt. Weder die Bindung der RNA and RhlB noch an den RhlB/RNase E Komplex scheint die Basenpaarung oder Konformation der RNA-Substrate zu beeinflussen, da lediglich eine homogene Peak-Verbreitung aller Imino-Protonen-Signale im 1H NMR-Spektrum beobachtet werden konnte.
Chapter I of this work addressed the piggyBac (PB) transposon system, a non-viral genome engineering tool that is capable of efficiently performing stable integration of DNA sequences into a target cells genome and has already been used in clinical trials. However, the PB transposase has the problematic property of preferentially integrating transposons near transcriptional start sites (TSSs). This increases the likelihood of causing genotoxic effects, limiting its potential use as a tool in clinical applications. It has been shown in the past that the PB transposase shows physical interactions with BET proteins (e.g. BRD4) through Co-IP experiments. Representatives of these proteins are part of the transcriptional activation complex and are abundant at TSSs. Accordingly, it was previously proposed that this interaction is the underlying cause for the biased integration preference. For the first chapter of this thesis, the goal was to disrupt this interaction potentially modifying said integration preference. A secondary structure hypothesized to be mainly responsible for said interaction was extensively mutated resulting in several PB variants that were analyzed for their interaction capacity through a series of Co-IP experiments with BRD4. In total, seven substitutions were identified (E380F, V390K, T392Y, M394R, K407C, K407Q, and K407V) which exhibited reduced interaction capacity with BRD4. Each of the aforementioned mutants were used to generate integration libraries and, through NGS, it was determined if the integration preferences of the respective mutants had changed. In the immediate range 200 base pairs up- and downstream from known TSSs all mutants used exhibited a reduced integration bias. At a wider observation window 3 kbp up- and downstream from TSSs, further mutants with the substitutions M394R, T392Y and V390K showed a reduction in integration frequency of 17.3%, 1.5% and 5.4%, respectively, compared to the wildtype. Of particular note was the M394R mutant, which showed a reduction in all window sizes analyzed with a maximum of 65% less integration preference in the immediate vicinity of TSSs, theoretically generating a safety advantage over the wildtype transposase.
Chapter II was dedicated to the overall safety improvement for transposon-based gene modification and addresses the time point after the transgene has already been integrated and serious side effects may not be preventable. With this in mind, the aim was to develop a novel suicide-switch that can be stably introduced into cells via transposition, and reliably leads to cell death of the modified cells once activated. A system based on CRISPR/Cas9 was developed, where single guide RNAs were used to guide the Cas9 nuclease to Alu elements. These are short, repetitive sequences, which are distributed over the human genome in more than one million copies. Inducing double strand breaks within these elements would lead to genomic fragmentation and cell death. To be inducible, a transcriptional as well as post- translational control mechanism was added. Transcription of the Cas9 nuclease was regulated using a tet-on system, making expression dependent on doxycycline (DOX) supplementation. Furthermore, a version of the Cas9 nuclease called arC9 was used that allows double strand break generation only in the presence of 4-Hydroxytamoxifen (4-HT). Together with an expression cassette for the Alu-specific guide RNA and an expression cassette for the reverse tetracycline controlled transactivator all components were arranged between transposase-specific recognition sequences on a plasmid to allow transposon-system based gene transfer. The system was tested in HeLa cells. First, conditional expression of the arC9 nuclease was confirmed by addition of 1 μg/ml DOX. Second, the suicide-switch was further induced by adding 200 nM 4-HT and protein extracts were assayed for the KAP1 phosphorylation. Only upon induction with DOX and 4-HT phosphorylated KAP1 was detected, indicating DNA damage. Further, extensive growth and survival experiments were conducted to determine the effect of suicide-switch induction on cell proliferation and survival. Between 24 and 48 hours after induction, a halt in cell division was detected, after which extensive cell death was observed. Within 5 days post induction, >99% of all cells were eliminated. In the absence of both inducers, no significant differences in survival were observed compared to control cells line lacking Alu-specific guide RNAs. Microscopic examinations of the <1% surviving cell fraction revealed a senescence-associated phenotype and showed no signs of resumption of the cell division process. Accordingly, the second chapter of this thesis also achieved its goal in developing a functional suicide-switch that can be inserted into human cells via transposition, is highly dependent on the necessary induction signals, and exhibits excellent elimination capabilities in the context tested.
Approximately 80 % of persistent wound infections are affected by the presence of bacterial biofilms, resulting in a severe clinical challenge associated with prolonged healing periods, increased morbidity, and high healthcare costs. Unfortunately, in vitro models for wound infection research almost exclusively focus on early infection stages with planktonic bacteria. In this study, we present a new approach to emulate biofilm-infected human wounds by three-dimensional human in vitro systems. For this purpose, a matured biofilm consisting of the clinical key wound pathogen Pseudomonas aeruginosa was pre-cultivated on electrospun scaffolds allowing for non-destructive transfer of the matured biofilm to human in vitro wound models. We infected tissue-engineered human in vitro skin models as well as ex vivo human skin explants with the biofilm and analyzed structural tissue characteristics, biofilm growth behavior, and biofilm-tissue interactions. The structural development of biofilms in close proximity to the tissue, resulting in high bacterial burden and in vivo-like morphology, confirmed a manifest wound infection on all tested wound models, validating their applicability for general investigations of biofilm growth and structure. The extent of bacterial colonization of the wound bed, as well as the subsequent changes in molecular composition of skin tissue, were inherently linked to the characteristics of the underlying wound models including their viability and origin. Notably, the immune response observed in viable ex vivo and in vitro models was consistent with previous in vivo reports. While ex vivo models offered greater complexity and closer similarity to the in vivo conditions, in vitro models consistently demonstrated higher reproducibility. As a consequence, when focusing on direct biofilm-skin interactions, the viability of the wound models as well as their advantages and limitations should be aligned to the particular research question of future studies. Altogether, the novel model allows for a systematic investigation of host-pathogen interactions of bacterial biofilms and human wound tissue, also paving the way for development and predictive testing of novel therapeutics to combat biofilm-infected wounds.
Approximately 80 % of persistent wound infections are affected by the presence of bacterial biofilms, resulting in a severe clinical challenge associated with prolonged healing periods, increased morbidity, and high healthcare costs. Unfortunately, in vitro models for wound infection research almost exclusively focus on early infection stages with planktonic bacteria. In this study, we present a new approach to emulate biofilm-infected human wounds by three-dimensional human in vitro systems. For this purpose, a matured biofilm consisting of the clinical key wound pathogen Pseudomonas aeruginosa was pre-cultivated on electrospun scaffolds allowing for non-destructive transfer of the matured biofilm to human in vitro wound models. We infected tissue-engineered human in vitro skin models as well as ex vivo human skin explants with the biofilm and analyzed structural tissue characteristics, biofilm growth behavior, and biofilm-tissue interactions. The structural development of biofilms in close proximity to the tissue, resulting in high bacterial burden and in vivo-like morphology, confirmed a manifest wound infection on all tested wound models, validating their applicability for general investigations of biofilm growth and structure. The extent of bacterial colonization of the wound bed, as well as the subsequent changes in molecular composition of skin tissue, were inherently linked to the characteristics of the underlying wound models including their viability and origin. Notably, the immune response observed in viable ex vivo and in vitro models was consistent with previous in vivo reports. While ex vivo models offered greater complexity and closer similarity to the in vivo conditions, in vitro models consistently demonstrated higher reproducibility. As a consequence, when focusing on direct biofilm-skin interactions, the viability of the wound models as well as their advantages and limitations should be aligned to the particular research question of future studies. Altogether, the novel model allows for a systematic investigation of host-pathogen interactions of bacterial biofilms and human wound tissue, also paving the way for development and predictive testing of novel therapeutics to combat biofilm-infected wounds.
Chromosomal translocations (CTs) are a genetic hallmark of cancer. They could be identified as recurrent genetic aberrations in hemato-malignancies and solid tumors. More than 40% of all “cancer genes” were identified in recurrent CTs. Most of these CTs result in the production of oncofusion proteins of which many have been studied over the past decades. They influence signaling pathways and/or alter gene expression. However, a precise mechanism for how these CTs arise and occur in a nearly identical fashion in individuals remains to be elucidated. Here, we performed experiments that explain the onset of CTs: (1) proximity of genes able to produce prematurely terminated transcripts, which lead to the production of (2) trans-spliced fusion RNAs, and finally, the induction of (3) DNA double-strand breaks which are subsequently repaired via EJ repair pathways. Under these conditions, balanced chromosomal translocations could be specifically induced. The implications of these findings will be discussed.
Synaptic transmission is a fundamental process that involves the transfer of information from a presynaptic neuron to a target cell through the release of neurotransmitters. The SV cycle is a complex series of events that enables the recycling of SVs, allowing for the sustained release of neurotransmitters. This process is mediated by a variety of proteins and enzymes, and its regulation is critical for maintaining proper synaptic function. Despite extensive research efforts, many aspects of the SV cycle and the underlying synaptic proteins remain poorly understood, highlighting the need for continued investigation into this important process. During this work, multiple aspects of synaptic transmission were studied by performing
behavioural, pharmacological, optogenetic, electrophysiological and ultrastructural assays on Caenorhabditis elegans. First, the role of two proteins (ERP-1 and RIMB-1) were analysed in the synaptic vesicle cycle. Second, a new optogenetic tool, the pOpsicle assay was described, which enables the direct visualization of synaptic vesicle (SV) release.
Activity-dependent bulk endocytosis (ADBE) enables the endocytosis of SV membrane and proteins in a fast manner during intense stimulation, resulting in bulk endosomes (also so-called large vesicles, LVs). Recycling proteins can be characterized by its site of action, whether they act at the plasma membrane (participating at the LV formation), or at the LV membrane (participating at the SV formation). ERP-1 (the C. elegans ortholog of Endophilin B) was recently identified as a possible SV recycling factor, its contribution to synaptic transmission has not been analysed before. During this project the function and possible cooperation of three proteins, ERP-1, UNC-57 (the C. elegans ortholog of Endophilin A) and CHC-1 (the C. elegans ortholog clathrin heavy chain) were studied, with a special emphasis of the site of action. It has been confirmed that these proteins participate together in synaptic vesicle recycling. Endophilins (ERP-1 and UNC-57) act both at the PM and the LV level, but while UNC-57 has been identified as the main player, ERP-1 rather has a minor role and acts as a back-up protein. CHC-1 functions the LV level in the first place, but it can compensate for the loss of UNC-57 and acts as a back-up protein at the PM.
RIM-binding protein is an evolutionarily conserved active zone protein, which interacts directly with RIM and N, P/Q, as well as L-type Ca2+ channels. RIM-BP and RIM have redundant functions in different model organisms including C. elegans, however, while the loss of UNC-10 (the C. elegans ortholog of RIM) led to drastic behavioural defects, the loss of RIMB-1 (the C. elegans ortholog of RIM-BP) led only to mild phenotypes. During this work the synaptic function of RIMB-1 and its interaction with UNC-10 and UNC-2 (C. elegans ortholog of the CaV2 1 subunit) were extensively investigated. It has been shown that RIMB-1 contributes to the precise localization of VGCCs in cooperation with UNC-10. Furthermore, it has been demonstrated, that RIMB-1 plays different roles in cholinergic and GABAergic neurons, thus it contributes to maintain a proper excitation/inhibition balance.
There are numerous available assays, which enable the indirect analysis of synaptic transmission, however, a tool, that enables the direct visualization of SV release, is highly desired. pOpsicle is a method which combines the optogenetic stimulation of cholinergic neurons with real-time visualization of SV release. A pH-sensitive fluorescence protein, pHuji, was inserted into the second intravesicular loop of the synaptic vesicle membrane protein, synaptogyrin (SNG-1). The fluorescence of pHuji is quenched inside the vesicles, but once they are released, the pH increases and pHuji can be detected. pOpsicle enables not only the direct visualization of SV exo-, and endocytosis events, but also the identification of putative SV recycling proteins.
In the past decade, the optogenetic toolbox for the manipulation of ion currents and cNMP levels in Caenorhabditis elegans (C. elegans) expanded. However, the implemented tools for cAMP generation were soluble enzymes (euPAC, bPAC, IlaC22 k27 and PaaC) and thus they do not precisely mimic physiological cAMP signalling occurring in microdomains in close proximity to the plasma membrane. Here, cAMP is predominantly generated by membrane-bound adenylyl cyclases, that are located in microdomains together with G protein-coupled receptors (GPCRs), protein kinase A (PKA) and their targets, enabling spatially and temporal regulation of cAMP signalling. For this reason, one aim of this study was to develop and implement membrane bound photoactivatable adenylyl cyclases for the manipulation of cAMP mediated signalling in close proximity to the plasma membrane. For this purpose, the guanylyl cyclase domains of the Blastocladiella and Catenaria Cyclase Opsins (CyclOps) were mutated to adenylyl cyclases either by introducing the mutations E497K and C566D (abbreviated as (A-2x)) or by the mutations E497K, H564D, and C566T (abbreviated as (A-3x)).
To determine the nucleotide specificity switch from GTP to ATP and the extent of light-dependent cAMP generation, the engineered enzymes were expressed in body wall muscle cells of C. elegans and in vitro cNMP measurements using C. elegans extracts were performed. Here, the highest levels of light induced cAMP generation during sustained stimulation (0.5 mW/mm2; 470 nm, 15 min) were detected for the variants BeCyclOp(A-2x), YFP-BeCyclOp(A-2x), and YFP-CaCyclOp(A-2x) (39, 57, 40 nM, respectively), though they did not reach the extent produced by the soluble bPAC (142 nM). In contrast, low magnitudes of generated cAMP were measured for the versions BeCyclOp(A-3x) and CaCyclOp(A-2x) (8 and 7 nM, respectively). Importantly, no obvious residual cGMP and basal activity was ascertained for any of the engineered enzymes.
To assess their potential to trigger and modulate cAMP mediated cholinergic neurotransmission, and to evaluate the influence of cytosolic and membrane proximal optogenetic cAMP generation, the enzymes were expressed in cholinergic motor neurons and compared to the implemented soluble bPAC via locomotion behaviour analysis on solid and in liquid media. Photoactivation of BeCyclOp(A-2x), YFP-BeCyclOp(A-2x), and YFP-CaCyclOp(A-2x) caused similarly enhanced or even more potent behavioural changes (swimming and crawling) as bPAC, whereas a more rapidly decaying response was observed for the bPAC evoked effects. Moreover, an increased diversity of the behavioural output was detected for cytosolic cAMP production by bPAC, i.e. increased bending angles and a decreased body length.
Confocal fluorescence microscopy was performed to examine the expression levels of YFP-tagged enzymes in cholinergic neurons, whereas both YFP-CyclOp(A-2x)s were expressed at similar levels, but 1.4-fold lower relative to the soluble bPAC-YFP. To compare the amount of light-dependent cAMP generation bPAC and BeCyclOp(A-2x) at light conditions that match the conditions of the behavioural experiments (30 s), cAMP measurements using C. elegans extracts were performed, whereas BeCyclOp(A-2x) depicted a 4-fold lower amount of optogenetic cAMP production than the soluble bPAC.
In sum, local (membrane proximal) cAMP generation by the membrane-bound photoactivatable adenylyl cyclases may more specifically activate cAMP dependent neurotransmission of cholinergic motor neurons than cytosolic cAMP generation, i.e. an increased mobilization and priming/docking of synaptic vesicles and an increased filling of the synaptic vesicles with the neurotransmitter acetylcholine and thus an increase in locomotion behaviour.
The optogenetic toolbox for the manipulation of cGMP mediated signalling in C. elegans consisted of the natural membrane-bound BeCyclOp and the artificial soluble bPGC. The latter generates cGMP with low efficiency and slow kinetics (~0.2 cGMP s-1), whereas BeCyclOp enables the production of much larger amounts of cGMP (L/D = 5000) at a high turnover rate (~17 cGMP s-1). Thus, one aim of this thesis was to implement a tool with features in between those of BeCyclOp and bPGC. Several orthologous CyclOps were assessed by Gao et al., 2015 for light-regulated cGMP production by in vitro assays based on the measurement of the cNMP content from CyclOp containing oocyte membranes. Here, CaCyclOp showed the highest ratio of light versus dark activity (L/D = 230) after BeCyclOp, and thus was selected for characterization in C. elegans...
mRNS ist einer der wichtigsten Informationsträger in lebenden Zellen. Mit ihr wird die in der DNS gespeicherte Information zu aktiven Zellprozessen umgesetzt. Dabei finden erste regulatorische Prozesse, die den Phänotyp eines Organismus bestimmen können, bereits über Strukturelemente auf der mRNS statt. Diese, als Riboschalter bezeichneten Strukturen, können spezifisch, kleine Moleküle binden und dadurch ihre Struktur ändern. Durch diese dynamische Änderung der Struktur, in An- oder Abwesenheit des Liganden, wird reguliert, ob nachfolgende Gene vom Ribosom abgelesen werden können. Der Cd1-Riboschalter aus Clostridium Difficile ist schon während der Transkription aktiv und ein Teil des regulatorischen Netzwerkes, das bestimmt, ob das Bakterium einen mobilen oder stationären Lebensstil einnimmt. Das zentrale Signalmolekül in diesem Netzwerk ist der sekundäre Botenstoff c-di-GMP, der gleichzeitig auch der Ligand des Cd1-Riboschalters ist. In der folgenden Arbeit wurde der zeitliche und strukturelle Ablauf des Cd1 Regulationsmechanismus und die Bindung von c-di-GMP untersucht. Auch ohne einen Riboschalter in der Sequenz ist strukturierte mRNS ein interessanter Forschungsgegenstand. Wie die Covid-19 Pandemie und die Forschungen, mRNS Abschnitte als Krebsmedikamente zu gebrauchen, zeigen, gewinnt RNS immer mehr an Bedeutung für die medizinische Forschung und Anwendung. Mit dieser Motivation im Hintergrund wurden drei weitere RNS Projekte bearbeitet. Im ersten wurde ein 19F-Screening für die Erkennung von RNS bindenden Fragmenten etabliert. Im zweiten wurde ein RNS Doppelstrang untersucht, der mit Hilfe verschiedener, kovalent gebundener Spiropyrane reversibel gefaltet und entfaltet werden sollte. Im abschließenden Projekt wurden im Rahmen der COVID-19-NMR Initiative zwei Sekundärstrukturelemente der Covid-19 RNS untersucht.
Bei der Untersuchung des Cd1-Riboschalters konnten folgende Ergebnisse erzielt werden. Es wird gezeigt, dass die Bindung von c-di-GMP an das Cd1-Aptamer ein konzentrationsabhängiges Magnesiumverhältnis braucht. Dieses Verhältnis wurde ausgehend von initialen Messungen als 1/40 (RNS/Ligand) bestimmt. Spätere ITC Messungen geben aber Hinweise darauf, dass dieses Verhältnis bei niedrigen RNS Konzentrationen höher liegt und bei größeren RNS Konzentrationen niedriger. Die Bestimmung des Start- und Endpunktes der c-di-GMP Bindung wird in Unterkapitel 3.1.2 behandelt. Es wurde ermittelt, dass Cd1 bei 83 Nukleotiden eine alternative schwach Ligand bindende Konformation einnimmt, die wahrscheinlich durch eine P1 Helix bis zum Erreichen von Cd1-87 stabilisiert wird. Ab Cd1-87 bildet sich die reguläre von der Literatur vorhergesagte Bindetasche. Das Ende der c-di-GMP Bindung wird mit Cd1-148 erreicht, auch wenn hier noch Reste der Reportersignale für Bindung zu sehen sind. Diese Reste werden aber aller Wahrscheinlichkeit nach durch eine Cd1-83 entsprechende Konformation der Bindetasche erzeugt. In Kapitel 3.2 wird gezeigt, wie durch NMR Messungen die Zuordnung der Sekundärstruktur des Cd1-Riboschalters vollzogen wurde. Durch diese Messungen konnte bestätigt werden, dass in allen Längen eine P2 und P3 Helix vorhanden ist. Im Aptamer wird die Ligandbindung durch zwei Interaktionen zwischen P2 und P3 stark stabilisiert und der untere Abschnitt der P3 erst dann nicht mehr dynamisch, wenn c-di-GMP gebunden wird. Durch x-filter Experimente und Mutationen konnte nachgewiesen werden, dass C87 das basenpaarende Nukleotid an einem G des Liganden ist. Die Anwesenheit des HP1 Stamms konnte in den Längen 147, 148 und 160 nachgewiesen werden, wobei besonders der Vergleich der NOESY Spektren von Cd1-147 und Cd1-148 die Änderung der Sekundärstruktur hin zum Antiterminator zeigen. Der Verlauf der Bindungsaffinitäten wurde auch durch ITC Messungen an Cd1-83, 86, 87, 88, 135 und 146 bestätigt. Für die volle Länge (Cd1-160) des Riboschalters konnte gezeigt werden, dass der Terminatorstamm ausgeformt ist. Die erreichten Ergebnisse wurden in einem Modell zusammengefasst und der zeitliche Verlauf der Cd1 Regulation simuliert. Aus der Simulation ist zu erkennen, dass Cd1, wie erwartet, Ligand abhängig schaltet. Dabei ist der Aus-Zustand bei hoher Ligandkonzentration zu 90% populiert und der An-Zustand zu 100% bei niedriger Konzentration. Des Weiteren konnte gezeigt werden, dass die Transkriptionsgeschwindigkeit bei hohen Ligandkonzentrationen einen starken Einfluss auf die Regulationseffizienz des Riboschalters hat. So ist bei einer Transkriptionsgeschwindigkeit von 100 nt/s nach 1 s eine Gleichverteilung von An- und Aus-Zustand zu erkennen. Dieses Verhalten kann durch einen Stopp der Transkription an der potentiellen Pausierstelle U141-145 aufgehoben werden. Unter den Rahmenbedingungen des Modells erwiesen sich Transkriptionsgeschwindkeiten von um die 20 nt/s als optimal und bei niedrigen Ligandkonzentrationen hatte die Transkriptionsgeschwindigkeit faktisch keine Auswirkungen auf die Regulation. Ein interessantes Ergebniss der Modellierung ergab sich aus der Notwendigkeit der Verwendung einer Rate für konkurrenzlose Basenpaarschließungen. Hier konnte gezeigt werden, dass eine Rate von 400 nt/s ausreicht um einen voll funktionsfähigen Riboschalter zu beschreiben.
Beim 19F Bindungsscreenings von 101 Fragmenten, die alle ein oder mehrere 19F Atome besaßen, an Cd1-98 wurden 9 Fragmente gefunden die an Cd1-98 binden. Diese sind größtenteils planar mit Ausnahme von 2 Fragmenten bei denen die eine Hälfte des Moleküls nicht aromatisch ist. Des Weiteren besitzen alle Fragmente, außer einem, mindestens eine Aminogruppe im Molekül. Die daraus resultierende Vermutung, dass die Fragmente in die RNS interkalieren, konnte durch RNS beobachtende NMR Messungen nicht überprüft werden, da keine Signaländerung im Imino-Bereich zu erkennen war. Durch Verdrängungsexperimente konnte gezeigt werden, dass die Fragmente, nicht wie c-di-GMP, die RNS Faltung homogenisieren und auch nicht in der Bindetasche gebunden werden.
Introns of human transfer RNA precursors (pre-tRNAs) are excised by the tRNA splicing endonuclease TSEN in complex with the RNA kinase CLP1. Mutations in TSEN/CLP1 occur in patients with pontocerebellar hypoplasia (PCH), however, their role in the disease is unclear. Here, we show that intron excision is catalyzed by tetrameric TSEN assembled from inactive heterodimers independently of CLP1. Splice site recognition involves the mature domain and the anticodon-intron base pair of pre-tRNAs. The 2.1-Å resolution X-ray crystal structure of a TSEN15–34 heterodimer and differential scanning fluorimetry analyses show that PCH mutations cause thermal destabilization. While endonuclease activity in recombinant mutant TSEN is unaltered, we observe assembly defects and reduced pre-tRNA cleavage activity resulting in an imbalanced pre-tRNA pool in PCH patient-derived fibroblasts. Our work defines the molecular principles of intron excision in humans and provides evidence that modulation of TSEN stability may contribute to PCH phenotypes.
»Die Entwicklung neuer Therapien ist bedeutungslos, wenn sie nicht von der Gesellschaft akzeptiert und angewendet werden. Wir haben dies während der jüngsten Pandemie deutlich erlebt. Daher liegt mir die Vermittlung wissenschaftlicher Erkenntnisse und die Förderung des Dialogs zwischen Wissenschaft und Gesellschaft sehr am Herzen. Veranstaltungen wie das Bürgersymposium spielen eine entscheidende Rolle, indem sie die Brücke zwischen der Forschung und der Öffentlichkeit schlagen«, sagte Prof. Windbergs im Nachgang des Bürgersymposiums. Diese Perspektiven spielen auch eine Rolle im Forschungscluster EMTHERA (EMerging THERApeutic strategies), in dem Prof. Windbergs mit sieben weiteren Wissenschaftler*innen der Goethe-Universität und der Johannes-Gutenberg-Universität das Steering Committee bildet. In enger Zusammenarbeit will das Forschungscluster mithilfe modernste RNA- und proximitätsinduzierender Technologien neue therapeutischer Strategien entwickeln, um die Behandlung von Infektionen mit RNA-Viren und multiresistenten Bakterien, die Eindämmung von Entzündungen und die Verbesserung der Gewebereparatur zu ermöglichen. Durch den Zusammenschluss zweier Parteien der Rhein-Main-Universitäten (RMU) werden komplementäre Expertisen vereint, um in einem interdisziplinären Ansatz hoch relevante Fragestellungen im Bereich neuer Therapiestrategien zu bearbeiten.
Major histocompatibility complex class I (MHC I) molecules present antigenic peptides to cytotoxic T cells to eliminate infected or cancerous cells. The transporter associated with antigen processing (TAP) shuttles proteasomally generated peptides into the ER for MHC I loading. As central part of the peptide-loading complex (PLC), TAP is targeted by viral factors, which inhibit peptide supply and thereby impact MHC I-mediated immune responses. However, it is still poorly understood how antigen presentation via different MHC I allotypes is affected by TAP inhibition. Here, we show that conditional expression of herpes simplex viral ICP47 suppresses surface presentation of HLA-A and HLA-C, but not of HLA-B, while the human cytomegaloviral US6 reduces surface levels of all MHC I allotypes. This marked difference in HLA-B antigen presentation is echoed by an enrichment of HLA-B allomorphs at US6-arrested PLC in comparison to ICP47-PLC. Although both viral factors prevent TAP-mediated peptide supply, our data imply that MHC I allomorphs favor different conformationally arrested states of the PLC, leading to differential downregulation of MHC I surface presentation. These findings will help understand MHC I biology in general and will even advance the targeted treatment of infections depending on patients’ allotypes.
Die Kernspinresonanz(NMR)-Spektroskopie ist ein leistungsstarkes analytisches Werkzeug. Allerdings ist ihre Empfindlichkeit aufgrund geringer Wechselwirkungs-energie zwischen den Kernspins und dem externen Magnetfeld begrenzt. Die dynamische Kernpolarisation (DNP) erhöht DNP die Empfindlichkeit der NMR, indem sie die Polarisation von ungepaarten Elektronenspins auf die benachbarten Kernspins überträgt. In den letzten Jahrzehnten hat die DNP bei hohen Magnetfeldern erneut an Aufmerksamkeit gewonnen, bedingt durch die Verfügbarkeit leistungsstarker Gyrotron-Mikrowellen(mw)-Quellen. Jedoch wurde die Anwendung von DNP für Flüssigkeiten im Vergleich zu Festkörperproben bei niedrigen Temperaturen (≈100 K) weit weniger erforscht. Zwei Gründe können dafür hauptsächlich benennt werden. Bei hohen Magnetfeldern (entsprechend hohen mw-Frequenzen) wird die mw-Strahlung sehr stark von Flüssigkeiten absorbiert, was zu einer starken Erwärmung führt. Darüber hinaus sind die Translations- und Rotationsdynamik der Radikale und Target-Molekülen nicht schnell genug, um Spectraldichten bei den hohen mw-Frequenzen zu erzeugen, die für eine Overhauser-Effekt (OE) DNP Verstärkung benötigt werden. In dieser Arbeit wird gezeigt, Flüssigzustands-DNP bei hohen Magnetfeldern, insbesondere bei 9,4 T, mit hocheffizienten DNP-Probenköpfen möglich ist.
Der von skalaren Hyperfein-Wechselwirkung (hfWW) angetriebene OE ist für Flüssigzustands-DNP-Forschungen von besonderem Interesse, da der von der Theorie vorhergesagte Mechanismus auch bei hohen Magnetfeldern noch effizient ist. In der vorliegenden Arbeit wurde eine Methode zur Vorabprüfung potenzieller DNP-Kandidaten durch Messungen ihrer paramagnetischen NMR-Verschiebungen vorgeschlagen und untersucht. Wir beobachtete signifikante 13C-skalare OE DNP-Verstärkungen bis zu 50 bei den ausgewählten kleinen Biomolekülen, einschließlich Imidazol, Indol, verschiedene Aminosäuren und Kohlenhydraten. Das Lösungssystem wurde auch von organischen Lösungsmitteln auf Wasser erweitert.
Im Kontext von dipolarer OE DNP haben wir den Beitrag der Rotation des Radikals neben der Translationsbewegung zwischen Radikal und Target-Molekül zur OE DNP-Effizienz systematisch untersucht, indem wir verschiedene Nitroxidderivate mit unterschiedlichen Ringgeometrien und Substituenten verwendet haben. Mithilfe eines Models, das eine 'out-sphere' Translationsbewegung und eine 'inner-sphere' Rotationsbewegung des Radikal-Lösungsmittel-Komplexes enthält, konnte unsere Beobachtungen quantitativ simuliert werden. Außerdem wurde ein anderes Model untersucht, das eine Translationsbewegung mit der Rotation von Radikalen, bei denen das ungepaarte Elektron nicht im Zentrum sitzt, kombiniert.
Eine weitere neue Entdeckung in der DNP bei hohen Magnetfeldern waren der beobachtete SE (Solid-Effekt) an Lipidmolekülen mit BDPA-Radikal oberhalb der Lipidphasen-übergangstemperatur. Die neue Anwendung von SE DNP bietet einen alternativen Mechanismus zur OE DNP in Flüssigkeiten bei hohen Magnetfeldern und könnte möglicherweise auf Makromoleküle mit relativ langsamer Rotationsbewegung angewendet werden.
Wir haben zusätzliche Untersuchungen an den Lipiddoppelschichten mit Nitroxid-radikale durchgeführt, basierend auf dem beobachteten 1H DNP-Verstärkungen in einer viskosen Lipidumgebung bei 9,4 T . Durch Messung des Feldprofils wurden DNP-Verstärkungen durch OE und SE in Abhängigkeit ihrer relativen Verschiebungen von der Elektronen-Larmor-Frequenz bestimmt. Die individuelle OE DNP-Effizienzen für Protonen des Wassers, der Lipid-Cholin-Kopfgruppen oder der Lipid-Acylketten wurde bestimmt. Dadurch wird ein quantitativer Vergleich mit MD-Simulationen ermöglicht. Obwohl die von der MD-Simulationen vorhergesagten DNP Kopplungsfaktoren noch deutliche Abweichungen von den experimentellen Beobachtungen aufweisen, wird die schnelle Dynamik nahe der Elektronen-Larmor-Frequenz, die für einen erfolgreichen OE DNP Transfer erforderlich ist, von den MD-Simulationen gut erfasst.
In der Arbeit wurden auch zwei unterschiedliche Dreifachresonanz-DNP-Experimente durchgeführt. Zum einen wurde 13C OE DNP unter 1H-Entkopplung in wässriger Natriumpyruvatlösung, und zum anderen 13C-NMR von Glycin, verstärkt durch SE DNP an 1H zusammen mit einem 1H-13C INEPT-Polarisationstransfer, im Rahmen dieser Doktorarbeit durchgeführt.
Photoresponsive hydrogels can be employed to coordinate the organization of proteins in three dimensions (3D) and thus to spatiotemporally control their physiochemical properties by light. However, reversible and user-defined tethering of proteins and protein complexes to biomaterials pose a considerable challenge as this is a cumbersome process, which, in many cases, does not support the precise localization of biomolecules in the z direction. Here, we report on the 3D patterning of proteins with polyhistidine tags based on in-situ two-photon lithography. By exploiting a two-photon activatable multivalent chelator head, we established the protein mounting of hydrogels with micrometer precision. In the presence of photosensitizers, a substantially enhanced two-photon activation of the developed tool inside hydrogels was detected, enabling the user-defined 3D protein immobilization in hydrogels with high specificity, micrometer-scale precision, and under mild light doses. Our protein-binding strategy allows the patterning of a wide variety of proteins and offers the possibility to dynamically modify the biofunctional properties of materials at defined subvolumes in 3D.
The role of lncRNAs in the CVS and the endothelium is highly diverse and has been subject to a substantial amount of research over the last decade. The identification of lncRNAs as clinically relevant biomarkers and as co-regulatory molecules let to the appreciation of the functional relevance of lncRNAs.
In the present study, LINC00607 was identified as an endothelial-enriched, human-specific lncRNA. With its distinct functions, LINC00607 maintains and supports the endothelial homeostasis especially in response to VEGF-A signalling.
In the first part of this study, LINC00607 was functionally characterized in human endothelial cells. LINC00607 is highly and specifically expressed in endothelial cells and is differentially regulated in CVDs. Depletion of LINC00607 resulted in decreased angiogenic sprouting, reduced integration of ECs in a newly formed vascular network in vivo, enhanced endothelial migration and differential expression of many important genes for endothelial cell homeostasis. Functionally, LINC00607 maintains ERG-driven endothelial gene expression programs through BRG1. BRG1 secures stably accessible enhancer regions as well as TSS of ERG target genes, thus enabling transcription of endothelial gene programs.
The second part of this study proposes an additional mode of action for LINC00607. The strongly impaired response to VEGF-A after LINC00607 KO can only be partially explained by its’ expression control of ERG target genes. It rather appears that LINC00607 is involved in the control of alternative splicing of VEGF receptor FLT1. The differential splicing of FLT1 produces the anti-angiogenic soluble isoform of FLT1. Even though further validation is needed to uncover the underlying mechanism, there is the potential of a more general role of LINC00607 in splicing control through BRG1. As AS of FLT1 is a clinical marker in preeclampsia, LINC00607 might qualify to be an additional marker for the onset and manifestation of the pregnancy disorder.
Taken together, LINC00607 is a target in future for molecular therapy in CVD to restore a healthy endothelial phenotype and has the potential to serve as a biomarker in preeclampsia.
Structural Biology has moved beyond the aim of simply identifying the components of a cellular subsystem towards analysing the dynamics and interactions of multiple players within a cell. This focal shift comes with additional requirements for the analytical tools used to investigate these systems of increased size and complexity, such as Native Mass Spectrometry, which has always been an important tool for structural biology. Scientific advance and recent developments, such as new ways to mimic a cell membrane for a membrane protein, have caused established methods to struggle to keep up with the increased demands. In this review, we summarize the possibilities, which Laser Induced Liquid Bead Ion Desorption (LILBID) mass spectrometry offers with regard to the challenges of modern structural biology, like increasingly complex sample composition, novel membrane mimics and advanced structural analysis, including next neighbor relations and the dynamics of complex formation.
ß-Hydroxybutyrate (BHB) is a ketone body formed in high amounts during lipolysis and fasting. Ketone bodies and the ketogenic diet were suggested as neuroprotective agents in neurodegenerative disease. In the present work, we induced transient ischemia in mouse brain by unilaterally occluding the middle cerebral artery for 90 min. BHB (30 mg/kg), given immediately after reperfusion, significantly improved the neurological score determined after 24 h. In isolated mitochondria from mouse brain, oxygen consumption by the complexes I, II and IV was reduced immediately after ischemia but recovered slowly over 1 week. The single acute BHB administration after reperfusion improved complex I and II activity after 24 h while no significant effects were seen at later time points. After 24 h, plasma and brain BHB concentrations were strongly increased while mitochondrial intermediates (citrate, succinate) were unchanged in brain tissue. Our data suggest that a single administration of BHB may improve mitochondrial respiration for 1–2 days but not for later time points. Endogenous BHB formation seems to complement the effects of exogenous BHB administration.
1H, 13C, and 15N backbone chemical shift assignments of coronavirus-2 non-structural protein Nsp10
(2020)
The international Covid19-NMR consortium aims at the comprehensive spectroscopic characterization of SARS-CoV-2 RNA elements and proteins and will provide NMR chemical shift assignments of the molecular components of this virus. The SARS-CoV-2 genome encodes approximately 30 different proteins. Four of these proteins are involved in forming the viral envelope or in the packaging of the RNA genome and are therefore called structural proteins. The other proteins fulfill a variety of functions during the viral life cycle and comprise the so-called non-structural proteins (nsps). Here, we report the near-complete NMR resonance assignment for the backbone chemical shifts of the non-structural protein 10 (nsp10). Nsp10 is part of the viral replication-transcription complex (RTC). It aids in synthesizing and modifying the genomic and subgenomic RNAs. Via its interaction with nsp14, it ensures transcriptional fidelity of the RNA-dependent RNA polymerase, and through its stimulation of the methyltransferase activity of nsp16, it aids in synthesizing the RNA cap structures which protect the viral RNAs from being recognized by the innate immune system. Both of these functions can be potentially targeted by drugs. Our data will aid in performing additional NMR-based characterizations, and provide a basis for the identification of possible small molecule ligands interfering with nsp10 exerting its essential role in viral replication.
The FUBP1-FUSE complex is an essential component of a transcription molecular machinery that is necessary for tight regulation of expression of many key genes including c-Myc and p21. FUBP1 utilizes its four articulated KH modules, which function cooperatively, for FUSE nucleotide binding. To understand molecular mechanisms fundamental to the intermolecular interaction, we present a set of crystal structures, as well ssDNA-binding characterization of FUBP1 KH domains. All KH1-4 motifs were highly topologically conserved, and were able to interact with FUSE individually and independently. Nevertheless, differences in nucleotide binding properties among the four KH domains were evident, including higher nucleotide-binding potency for KH3 as well as diverse nucleotide sequence preferences. Variations in amino acid compositions at one side of the binding cleft responsible for nucleobase resulted in diverse shapes and electrostatic charge interaction, which might feasibly be a contributing factor for different nucleotide-binding propensities among KH1-4. Nonetheless, conservation of structure and nucleotide-binding property in all four KH motifs is essential for the cooperativity of multi KH modules present in FUBP1 towards nanomolar affinity for FUSE interaction. Comprehensive structural comparison and ssDNA binding characteristics of all four KH domains presented here provide molecular insights at a fundamental level that might be beneficial for elucidating the mechanisms of the FUBP1-FUSE interaction.
Bislang sind die strukturellen Voraussetzungen für die Selektivität von Agonisten an den Retinoid Rezeptor Subtypen RXRα, RXRβ und RXRγ kaum erforscht, obwohl RXR-Modulatoren, die eine Subtypen-Präferenz aufweisen, aufgrund der unterschiedlichen Expressionsmuster der Subtypen Gewebe-spezifische Effekte vermitteln und somit Nebenwirkungen verringern könnten. Der Grund dieser Forschungslücke liegt teilweise darin, dass die Entwicklung Subtypen-selektiver RXR-Agonisten aufgrund der enormen strukturellen Ähnlichkeit der Ligandbindestellen in den RXR-Subtypen - alle Aminosäuren, die die Bindungsstellen bilden sind identisch - als unerreichbar angesehen wurde. Die Entdeckung des Naturstoffs Valerensäure als RXR-Agonist mit ausgeprägter Präferenz für den RXRβ-Subtyp hat jedoch gezeigt, dass Subtypen-selektive RXR-Modulation möglich ist249 und SAR-Studien an unterschiedlichen RXR-Ligand-Chemotypen haben in der Folge bestätigt, dass die Entwicklung von RXR-Liganden mit Subtypen-Präferenz erreicht werden kann.
Auf der Basis von Valerensäure und der in früheren Arbeiten entwickelten RXR-Agonisten wurden in dieser Arbeit Strukturmodifikationen identifiziert, die zu einer RXR-Subtypen-Präferenz beitragen. Durch die Verschmelzung dieser Strukturelemente ist es gelungen, einen neuen RXR-Agonist-Chemotyp (A) zu entwerfen, der durch strategische Methylierung und weitere Strukturmodifikationen zur Präferenz für jeden Subtyp optimiert werden konnte.
In einem Adipozyten-Differenzierungsexperiment konnte gezeigt werden, dass RXRα der wichtigste Heterodimer-Partner von PPARγ während der Adipogenese ist. Ferner unterstrich diese biologische Untersuchung das Potenzial von 99, 103 und 105 als Subtyp-präferentielle RXR-Agonisten in vitro Experimenten zu dienen.
Auf der Grundlage dieser Ergebnisse wurde eine mögliche Rolle von Acrylsäurepartialstrukturen natürlicher RXR-Liganden basierend auf dem zuvor entwickelten Chemotyp untersucht. Hierzu wurden das α-Methylacrylsäuremotiv des Naturstoffs Valerensäure (18) und das β-Methylacrylsäuremotiv des endogenen RXR-Agonisten 9-cis-Retinsäure in den Chemotyp A integriert (Chemotyp B), um die Rolle dieser Acrylsäuregruppen bei der Vermittlung der RXR-Subtypen-Selektivität zu untersuchen. Die Strukturmodifikationen an B zeigten, dass nur die α-Methyl-substituierte Acrylsäurekette toleriert bzw. von RXRβ präferiert wurde, was die RXR-Präferenz der Valerensäure (18) unterstützte.
In dieser Arbeit konnte gezeigt werden, dass RXR-Liganden mit Subtypen-Präferenz realisierbar sind und durch gezielte Strukturmodifikationen in ihrer Präferenz gesteuert werden können. Die Erkenntnisse zu den Struktur-Wirkungs-Beziehungen der neuen RXR-Agonist-Chemotypen A und B erweitern den Wissenstand über die strukturellen Voraussetzungen von RXR-Liganden für die Subtypen-Präferenz deutlich.
This cumulative dissertation examines learning in chemistry laboratories, focusing on the challenges and benefits of problem-based learning (PBL) for novices in the lab. It addresses the lack of consistent understanding about what should be learned in labs and why it's important. The research aims to understand what students learn, how they learn, and how lab learning can be improved.
A central concept in PBL labs is Information Literacy, defined as a sociocultural practice enabling learners to identify and use information sources within a specific context as legitimized by the practice community.
The first publication, Wellhöfer and Lühken (2022a), investigates the relationship between PBL and learner motivation. It identifies factors that can foster students' intrinsic motivation in a PBL lab. Autonomy is found to be a key factor, increasing student motivation and presenting a model of the autonomous scientific process. This model involves four steps: information acquisition, designing and applying experimental procedures, experimental feedback, and autonomous process optimization. The results suggest that intrinsic motivation in PBL labs can be enhanced by enabling students to independently execute these steps.
The second publication, Wellhöfer and Lühken (2022b), examines the information process students undergo during their first PBL lab. Using a sociocultural framework, it explores Information Literacy to understand students' handling of information and their perceptions of the information process. The findings reveal that in PBL labs, developing a practical, applicable experimental procedure is crucial for problem-solving and significantly shapes the information-acquisition process. This process is iterative, influenced by new information, leading to more precise information needs. Students assess information quality based on its usefulness for their problem, implementability (considering cognitive understanding, available equipment, and psychomotor skills), and safety.
Furthermore, the role of privileged knowledge forms in evaluating the quality of text sources is explored. Students viewed non-scientific sources as "poor" and scientific sources as "good," yet used both for information gathering. There were discrepancies between their assessment of source quality and actual use, indicating that perception of source quality doesn't always affect their practical decisions.
The third publication, Wellhöfer, Machleid, and Lühken (2023), investigates students' information practices in the lab, focusing on discourse between novice learners and experienced assistants. It shows that theoretical knowledge isn't sufficient for independent practical action, and students need actionable social information from experienced community members. The results highlight that information literacy in the lab for newcomers to a community of practice has distinctive features, and physical experience and tacit knowledge are crucial for learning the methods and group-specific knowledge of the practice community. The article demonstrates how learning information literacy in a practice community requires a social and physical experience and provides insights on how educators can support this process.
Phenotypical screening is a widely used approach in drug discovery for the identification of small molecules with cellular activities. However, functional annotation of identified hits often poses a challenge. The development of small molecules with narrow or exclusive target selectivity such as chemical probes and chemogenomic (CG) libraries, greatly diminishes this challenge, but non-specific effects caused by compound toxicity or interference with basic cellular functions still pose a problem to associate phenotypic readouts with molecular targets. Hence, each compound should ideally be comprehensively characterized regarding its effects on general cell functions. Here, we report an optimized live-cell multiplexed assay that classifies cells based on nuclear morphology, presenting an excellent indicator for cellular responses such as early apoptosis and necrosis. This basic readout in combination with the detection of other general cell damaging activities of small molecules such as changes in cytoskeletal morphology, cell cycle and mitochondrial health provides a comprehensive time-dependent characterization of the effect of small molecules on cellular health in a single experiment. The developed high-content assay offers multi-dimensional comprehensive characterization that can be used to delineate generic effects regarding cell functions and cell viability, allowing an assessment of compound suitability for subsequent detailed phenotypic and mechanistic studies.
Publicly available compound and bioactivity databases provide an essential basis for data-driven applications in life-science research and drug design. By analyzing several bioactivity repositories, we discovered differences in compound and target coverage advocating the combined use of data from multiple sources. Using data from ChEMBL, PubChem, IUPHAR/BPS, BindingDB, and Probes & Drugs, we assembled a consensus dataset focusing on small molecules with bioactivity on human macromolecular targets. This allowed an improved coverage of compound space and targets, and an automated comparison and curation of structural and bioactivity data to reveal potentially erroneous entries and increase confidence. The consensus dataset comprised of more than 1.1 million compounds with over 10.9 million bioactivity data points with annotations on assay type and bioactivity confidence, providing a useful ensemble for computational applications in drug design and chemogenomics.
Dimerization of Taspase1 activates an intrinsic serine protease function that leads to the catalytic Thr234 residue, which allows to catalyze the consensus sequence Q−3X−2D−1⋅G1X2D3D4, present in Trithorax family members and TFIIA. Noteworthy, Taspase1 performs only a single hydrolytic step on substrate proteins, which makes it impossible to screen for inhibitors in a classical screening approach. Here, we report the development of an HTRF reporter assay that allowed the identification of an inhibitor, Closantel sodium, that inhibits Taspase1 in a noncovalent fashion (IC50 = 1.6 μM). The novel inhibitor interferes with the dimerization step and/or the intrinsic serine protease function of the proenzyme. Of interest, Taspase1 is required to activate the oncogenic functions of the leukemogenic AF4-MLL fusion protein and was shown in several studies to be overexpressed in many solid tumors. Therefore, the inhibitor may be useful for further validation of Taspase1 as a target for cancer therapy.
Unraveling the activation mechanism of taspase1 which controls the oncogenic AF4–MLL fusion protein
(2015)
We have recently demonstrated that Taspase1-mediated cleavage of the AF4–MLL oncoprotein results in the formation of a stable multiprotein complex which forms the key event for the onset of acute proB leukemia in mice. Therefore, Taspase1 represents a conditional oncoprotein in the context of t(4;11) leukemia. In this report, we used site-directed mutagenesis to unravel the molecular events by which Taspase1 becomes sequentially activated. Monomeric pro-enzymes form dimers which are autocatalytically processed into the enzymatically active form of Taspase1 (αββα). The active enzyme cleaves only very few target proteins, e.g., MLL, MLL4 and TFIIA at their corresponding consensus cleavage sites (CSTasp1) as well as AF4–MLL in the case of leukemogenic translocation. This knowledge was translated into the design of a dominant-negative mutant of Taspase1 (dnTASP1). As expected, simultaneous expression of the leukemogenic AF4–MLL and dnTASP1 causes the disappearance of the leukemogenic oncoprotein, because the uncleaved AF4–MLL protein (328 kDa) is subject to proteasomal degradation, while the cleaved AF4–MLL forms a stable oncogenic multi-protein complex with a very long half-life. Moreover, coexpression of dnTASP1 with a BFP-CSTasp1-GFP FRET biosensor effectively inhibits cleavage. The impact of our findings on future drug development and potential treatment options for t(4;11) leukemia will be discussed.
Over the last 15 years the Diagnostic Center of Acute Leukemia (DCAL) at the Frankfurt University has diagnosed and elucidated the Mixed Lineage Leukemia (MLL) recombinome with >100 MLL fusion partners. When analyzing all these different events, balanced chromosomal translocations were found to comprise the majority of these cases (~70%), while other types of genetic rearrangements (3-way-translocations, spliced fusions, 11q inversions, interstitial deletions or insertion of chromosomal fragments into other chromosomes) account for about 30%. In nearly all those complex cases, functional fusion proteins can be produced by transcription, splicing and translation. With a few exceptions (10 out of 102 fusion genes which were per se out-of-frame), all these genetic rearrangements produced a direct MLL fusion gene, and in 94% of cases an additional reciprocal fusion gene. So far, 114 patients (out of 2454 = ~5%) have been diagnosed only with the reciprocal fusion allele, displaying no MLL-X allele. The fact that so many MLL rearrangements bear at least two fusion alleles, but also our findings that several direct MLL fusions were either out-of-frame fusions or missing, raises the question about the function and importance of reciprocal MLL fusions. Recent findings also demonstrate the presence of reciprocal MLL fusions in sarcoma patients. Here, we want to discuss the role of reciprocal MLL fusion proteins for leukemogenesis and beyond.
Mechanistic characterization of photoisomerization reactions in organic molecules and photoreceptors
(2023)
In dieser Arbeit wurden verschiedene Einflüsse auf die Dynamik von Photoisomerisierungen in Phytochromen und indigoiden Photoschaltern untersucht. Beide Forschungsgebiete teilen wesentliche Aspekte wie die Kontrolle durch sterische Wechselwirkungen und den starken Einfluss der Polarität oder der ionischen Umgebung.
Auf dem Gebiet der Phytochrome wurde die relative Positionierung der knotenlosen Phytochrome innerhalb der Superfamilie der Phytochrome in Bezug auf ihre Photodynamik und den Effekt von Grundzustandsheterogenität herausgearbeitet. Es wurde anhand von ultraschnellen, zeitaufgelösten Anrege-Abtast-Experimenten der einzelnen GAF-Domäne All2699g1 im Vergleich mit dem vollständigen knotenlosen Phytochrom All2699g1g2 und dem strukturell ähnlichen knotenlosen Phytochrom SynCph2 gezeigt, dass knotenlose Phytochrome in ihrer Vorwärtsdynamik eine komplexe mehrphasige Kinetik mit einem langlebigen angeregten Zustand (~100 ps) aufweisen. Die beobachtete mehrphasige Kinetik konnte einer initialen Chromophordynamik sowie einer nicht exponentiellen Reorganisation der chromophor-umgebenden Proteinmatrix zugeordnet werden. Dies steht im starken Kontrast zur im Gebiet der Phytochrome etablierten Beschreibung derartiger mehrphasiger Kinetiken mittels heterogener Grundzustände. Stattdessen wurde ein konserviertes kinetisches Muster identifiziert, welches die mehrphasige Dynamik beschreibt und in allen in dieser Arbeit untersuchten Phytochrome beobachtet wurde. Zudem konnte dieses Muster in einem Phytochrom der Gruppe I und einem Phytochrom der Gruppe III, die einen ähnlichen Pr Dunkelzustand aufweisen, gezeigt werden, was eine breite Anwendbarkeit des damit verbundenen Mechanismus vermuten lässt. Weiterhin konnte die zentrale Rolle eines konservierten Tyrosins in der Photoisomerisierung anhand von Mutationsstudien in All2699g1 herausgearbeitet werden. Diese konservierte Aminosäure muss im Rahmen der Reorganisation der Proteinmatrix vom Chromophor weggezogen werden, damit die sterische Blockade abgebaut werden kann, die die Isomerisierung des Chromophors zunächst verhindert. Da diese Bewegung von diversen Faktoren in der den Chromophor umgebenden Proteinmatrix abhängt, weist sie eine nicht exponentielle Kinetik auf, die je nach Phytochrom, der spezifischen Flexibilität und dem vorhandenen Raum in der Bindetasche unterschiedliche Lebenszeiten aufweist.
Die Rückreaktion knotenloser Phytochrome konnte ebenfalls im Rahmen dieser Arbeit charakterisiert werden, welche im Pikosekundenbereich abläuft, und damit signifikant schneller ist als die Vorwärtsreaktion. Im Gegensatz zur Vorwärtsreaktion nimmt Grundzustandsheterogenität in der Rückreaktion eine weitaus bedeutendere Rolle ein. Hier weisen die in All2699g1 vorhandenen heterogenen Grundzustandspopulationen jeweils eine eigene Kinetik ihres angeregten Zustands auf, während die homogenen Grundzustände von All2699g1g2 und SynCph2 jeweils nur einen Zerfall des angeregten Zustands zeigen. Der Ursprung dieser Heterogenität konnte im Wasserstoffbrückennetzwerk des Chromophors lokalisiert und mit dem konservierten Tyrosin und einem konservierten Serin in der PHY-Domäne verknüpft werden. Die Anwesenheit der PHY-Domäne sorgt demnach für eine Verringerung der Grundzustandsheterogenität und des vorhandenen Raums in der Bindetasche, wodurch die Effizienz der Photoreaktion optimiert wird.
Zuletzt konnte die Millisekundendynamik knotenloser Phytochrome und der Einfluss der PHY-Domäne auf diese aufgeklärt werden. Die PHY-Domäne sorgt hierbei durch den verringerten Raum in der Bindetasche dafür, dass die zunächst stattfindende thermische Relaxation des Chromophors signifikant verlangsamt wird, während spätere Änderungen im Photozyklus nur wenig beeinflusst werden.
Auf dem Gebiet der indigoiden Photoschalter konnte, anhand eines sterisch überladenen Hemithioindigo Photoschalters, der Photoisomerisierungsmechanismus des Hula-Twists beobachtet und eine starke Lösungsmittelabhängigkeit der entsprechenden Kinetik aufgezeigt werden. Aus den durchgeführten zeitaufgelösten Anrege-Abtast-Experimenten in verschiedenen Lösungsmitteln konnte ein Modell für die Photodynamik des verwendeten Hemithioindigo Photoschalters entwickelt werden. In unpolaren Lösungsmitteln muss eine hohe Barriere zur produktiven konischen Durchschneidung überwunden werden, was zu Lebenszeiten des angeregten Zustands im Nanosekundenbereich führt. Der Weg zur produktiven konischen Durchschneidung folgt dabei dem Hula-Twist Mechanismus. Dieser Pfad ist in polaren Lösungsmitteln unerreichbar, weshalb eine schnelle Relaxation über eine unproduktive konische Durchschneidung stattfindet.
Im zweiten Projekt auf dem Gebiet der indigoiden Photoschalter wurde anhand der neuartigen Klasse der Iminothioindoxyl Photoschalter ein Schwingungsenergiedonor für Schwingungsenergietransferstudien entwickelt. Das daraus entwickelte Modellsystem, bestehend aus einer künstlichen Aminosäure auf Basis des Iminothioindoxyl Photoschalters und einem daran gekoppelten Schwingungsenergiesensor, wurde charakterisiert und die primäre Photoreaktion untersucht. Es konnte gezeigt werden, dass der angeregte Zustand des Modellsystems kurzlebig ist und unter Abgabe von großen Mengen an Schwingungsenergie zerfällt, unabhängig von der Anregungswellenlänge und dem verwendeten Lösungsmittel. Somit zeigt das entwickelte System vorteilhafte Eigenschaften für Schwingungsenergietransferstudien.
Insgesamt konnten somit die Mechanismen der Photoisomerisierungsreaktionen in knotenlosen Phytochromen und indigoiden Photoschaltern aufgeklärt und daraus die Relevanz der Umgebung für derartige Reaktionen herausgearbeitet werden.
Glucose hypometabolism, mitochondrial dysfunction, and cholinergic deficits have been reported in early stages of Alzheimer’s disease (AD). Here, we examine these parameters in TgF344-AD rats, an Alzheimer model that carries amyloid precursor protein and presenilin-1 mutations, and of wild type F344 rats. In mitochondria isolated from rat hippocampi, we found reductions of complex I and oxidative phosphorylation in transgenic rats. Further impairments, also of complex II, were observed in aged (wild-type and transgenic) rats. Treatment with a “cocktail” containing magnesium orotate, benfotiamine, folic acid, cyanocobalamin, and cholecalciferol did not affect mitochondrial activities in wild-type rats but restored diminished activities in transgenic rats to wild-type levels. Glucose, lactate, and pyruvate levels were unchanged by age, genetic background, or treatment. Using microdialysis, we also investigated extracellular concentrations of acetylcholine that were strongly reduced in transgenic animals. Again, ACh levels in wild-type rats did not change upon treatment with nutrients, whereas the cocktail increased hippocampal acetylcholine levels under physiological stimulation. We conclude that TgF344-AD rats display a distinct mitochondrial and cholinergic dysfunction not unlike the findings in patients suffering from AD. This dysfunction can be partially corrected by the application of the “cocktail” which is particularly active in aged rats. We suggest that the TgF344-AD rat is a promising model to further investigate mitochondrial and cholinergic dysfunction and potential treatment approaches for AD.
Cytochrome c oxidase catalyzes the reduction of oxygen to water. This process is accompanied by the vectorial transport of protons across the mitochondrial or bacterial membrane (“proton pumping”). The mechanism of proton pumping is still a matter of debate. Many proposed mechanisms require structural changes during the reaction cycle of cytochrome c oxidase. Therefore, the structure of the cytochrome c oxidase was determined in the completely oxidized and in the completely reduced states at a temperature of 100 K. No ligand exchanges or other major structural changes upon reduction of the cytochrome coxidase from Paracoccus denitrificans were observed. The three histidine CuB ligands are well defined in the oxidized and in the reduced states. These results are hardly compatible with the “histidine cycle” mechanisms formulated previously.
The potential of a protein-engineered His tag to immobilize macromolecules in a predictable orientation at metal-chelating lipid interfaces was investigated using recombinant 20 S proteasomes His-tagged in various positions. Electron micrographs demonstrated that the orientation of proteasomes bound to chelating lipid films could be controlled via the location of their His tags: proteasomes His-tagged at their sides displayed exclusively side-on views, while proteasomes His-tagged at their ends displayed exclusively end-on views. The activity of proteasomes immobilized at chelating lipid interfaces was well preserved. In solution, His-tagged proteasomes hydrolyzed casein at rates comparable with wild-type proteasomes, unless the His tags were located in the vicinity of the N termini of α-subunits. The N termini of α-subunits might partly occlude the entrance channel in α-rings through which substrates enter the proteasome for subsequent degradation. A combination of electron micrographs and atomic force microscope topographs revealed a propensity of vertically oriented proteasomes to crystallize in two dimensions on fluid lipid films. The oriented immobilization of His-tagged proteins at biocompatible lipid interfaces will assist structural studies as well as the investigation of biomolecular interaction via a wide variety of surface-sensitive techniques including single-molecule analysis.
ATP-binding cassette (ABC) systems translocate a wide range of solutes across cellular membranes. The thermophilic Gram-negative eubacterium Thermus thermophilus, a model organism for structural genomics and systems biology, discloses ∼46 ABC proteins, which are largely uncharacterized. Here, we functionally analyzed the first two and only ABC half-transporters of the hyperthermophilic bacterium, TmrA and TmrB. The ABC system mediates uptake of the drug Hoechst 33342 in inside-out oriented vesicles that is inhibited by verapamil. TmrA and TmrB form a stable heterodimeric complex hydrolyzing ATP with a Km of 0.9 mm and kcat of 9 s−1 at 68 °C. Two nucleotides can be trapped in the heterodimeric ABC complex either by vanadate or by mutation inhibiting ATP hydrolysis. Nucleotide trapping requires permissive temperatures, at which a conformational ATP switch is possible. We further demonstrate that the canonic glutamate 523 of TmrA is essential for rapid conversion of the ATP/ATP-bound complex into its ADP/ATP state, whereas the corresponding aspartate in TmrB (Asp-500) has only a regulatory role. Notably, exchange of this single noncanonic residue into a catalytic glutamate cannot rescue the function of the E523Q/D500E complex, implicating a built-in asymmetry of the complex. However, slow ATP hydrolysis in the newly generated canonic site (D500E) strictly depends on the formation of a posthydrolysis state in the consensus site, indicating an allosteric coupling of both active sites.
The ATP-binding cassette half-transporter Mdl1 from Saccharomyces cerevisiae has been proposed to be involved in the quality control of misassembled respiratory chain complexes by exporting degradation products generated by the m-AAA proteases from the matrix. Direct functional or structural data of the transport complex are, however, not known so far. After screening expression in various hosts, Mdl1 was overexpressed 100-fold to 1% of total mitochondrial membrane protein in S. cerevisiae. Based on detergent screens, Mdl1 was solubilized and purified to homogeneity. Mdl1 showed a high binding affinity for MgATP (Kd = 0.26 μm) and an ATPase activity with a Km of 0.86 mm (Hill coefficient of 0.98) and a turnover rate of 2.6 ATP/s. Mutagenesis of the conserved glutamate downstream of the Walker B motif (E599Q) or the conserved histidine of the H-loop (H631A) abolished ATP hydrolysis, whereas ATP binding was not affected. Mdl1 reconstituted into liposomes showed an ATPase activity similar to the solubilized complex. By single particle electron microscopy, a first three-dimensional structure of the mitochondrial ATP-binding cassette transporter was derived at 2.3-nm resolution, revealing a homodimeric complex in an open conformation.
The ABC transporter Mdl1p, a structural and functional homologue of the transporter associated with antigen processing (TAP) plays an important role in intracellular peptide transport from the mitochondrial matrix of Saccharomyces cerevisiae. To characterize the ATP hydrolysis cycle of Mdl1p, the nucleotide-binding domain (NBD) was overexpressed in Escherichia coli and purified to homogeneity. The isolated NBD was active in ATP binding and hydrolysis with a turnover of 25 ATP per minute and a Km of 0.6 mm and did not show cooperativity in ATPase activity. However, the ATPase activity was non-linearly dependent on protein concentration (Hill coefficient of 1.7), indicating that the functional state is a dimer. Dimeric catalytic transition states could be trapped either by incubation with orthovanadate or beryllium fluoride, or by mutagenesis of the NBD. The nucleotide composition of trapped intermediate states was determined using [alpha-32P]ATP and [gamma-32P]ATP. Three different dimeric intermediate states were isolated, containing either two ATPs, one ATP and one ADP, or two ADPs. Based on these experiments, it was shown that: (i) ATP binding to two NBDs induces dimerization, (ii) in all isolated dimeric states, two nucleotides are present, (iii) phosphate can dissociate from the dimer, (iv) both nucleotides are hydrolyzed, and (v) hydrolysis occurs in a sequential mode. Based on these data, we propose a processive-clamp model for the catalytic cycle in which association and dissociation of the NBDs depends on the status of bound nucleotides.
The purification and functional reconstitution of a five-component oligopeptide ATP-binding cassette transporter with a remarkably wide substrate specificity are described. High-affinity peptide uptake was dependent on liganded substrate-binding protein OppA, which interacts with the translocator OppBCDF with higher affinity than unliganded OppA. Transport screening with combinatorial peptide libraries revealed that (i) the Opp transporter is not selective with respect to amino acid side chains of the transported peptides; (ii) any peptide that can bind to OppA is transported via Opp, including very long peptides up to 35 residues long; and (iii) the binding specificity of OppA largely determines the overall transport selectivity.
The transporter associated with antigen processing (TAP) plays a key role in the adaptive immune response by pumping antigenic peptides into the endoplasmic reticulum for subsequent loading of major histocompatibility complex class I molecules. TAP is a heterodimer consisting of TAP1 and TAP2. Each subunit is composed of a transmembrane domain and a nucleotide-binding domain, which energizes the peptide transport. To analyze ATP hydrolysis of each subunit we developed a method of trapping 8-azido-nucleotides to TAP in the presence of phosphate transition state analogs followed by photocross-linking, immunoprecipitation, and high resolution SDS-PAGE. Strikingly, trapping of both TAP subunits by beryllium fluoride is peptide-specific. The peptide concentration required for half-maximal trapping is identical for TAP1 and TAP2 and directly correlates with the peptide binding affinity. Only a background level of trapping was observed for low affinity peptides or in the presence of the herpes simplex viral protein ICP47, which specifically blocks peptide binding to TAP. Importantly, the peptide-induced trapped state is reached after ATP hydrolysis and not in a backward reaction of ADP binding and trapping. In the trapped state, TAP can neither bind nor exchange nucleotides, whereas peptide binding is not affected. In summary, these data support the model that peptide binding induces a conformation that triggers ATP hydrolysis in both subunits of the TAP complex within the catalytic cycle.
The lysosomal ABC transporter associated with antigen processing-like (TAPL, ABCB9) acts as an ATP-dependent polypeptide transporter with broad length selectivity. To characterize in detail its substrate specificity, a procedure for functional reconstitution of human TAPL was developed. By intensive screening of detergents, ideal solubilization conditions were evolved with respect to efficiency, long term stability, and functionality of TAPL. TAPL was isolated in a two-step procedure with high purity and, subsequently, reconstituted into proteoliposomes. The peptide transport activity of reconstituted TAPL strongly depends on the lipid composition. With the help of combinatorial peptide libraries, the key positions of the peptides were localized to the N- and C-terminal residues with respect to peptide transport. At both ends, TAPL favors positively charged, aromatic, or hydrophobic residues and disfavors negatively charged residues as well as asparagine and methionine. Besides specific interactions of both terminal residues, electrostatic interactions are important, since peptides with positive net charge are more efficiently transported than negatively charged ones.
The transporter associated with antigen processing (TAP) translocates antigenic peptides from the cytosol into the endoplasmic reticular lumen for subsequent loading onto major histocompatibility complex (MHC) class I molecules. These peptide-MHC complexes are inspected at the cell surface by cytotoxic T-lymphocytes. Assembly of the functional peptide transport and loading complex depends on intra- and intermolecular packing of transmembrane helices (TMs). Here, we have examined the membrane topology of human TAP1 within an assembled and functional transport complex by cysteine-scanning mutagenesis. The accessibility of single cysteine residues facing the cytosol or endoplasmic reticular lumen was probed by a minimally invasive approach using membrane-impermeable, thiol-specific fluorophores in semipermeabilized “living” cells. TAP1 contains ten transmembrane segments, which place the N and C termini in the cytosol. The transmembrane domain consists of a translocation core of six TMs, a building block conserved among most ATP-binding cassette transporters, and a unique additional N-terminal domain of four TMs, essential for tapasin binding and assembly of the peptide-loading complex. This study provides a first map of the structural organization of the TAP machinery within the macromolecular MHCI peptide-loading complex.
P2X1 receptor subunits assemble in the ER of Xenopus oocytes to homotrimers that appear as ATP-gated cation channels at the cell surface. Here we address the extent to which N-glycosylation contributes to assembly, surface appearance, and ligand recognition of P2X1receptors. SDS-polyacrylamide gel electrophoresis (PAGE) analysis of glycan minus mutants carrying Gln instead of Asn at five individual NXT/S sequons reveals that Asn284 remains unused because of a proline in the +4 position. The four other sites (Asn153, Asn184, Asn210, and Asn300) carryN-glycans, but solely Asn300 located only eight residues upstream of the predicted reentry loop of P2X1acquires complex-type carbohydrates. Like parent P2X1, glycan minus mutants migrate as homotrimers when resolved by blue native PAGE. Recording of ATP-gated currents reveals that elimination of Asn153 or Asn210 diminishes or increases functional expression levels, respectively. In addition, elimination of Asn210 causes a 3-fold reduction of the potency for ATP. If three or all four N-glycosylation sites are simultaneously eliminated, formation of P2X1 receptors is severely impaired or abolished, respectively. We conclude that at least oneN-glycan per subunit of either position is absolutely required for the formation of P2X1 receptors and that individual N-glycans possess marked positional effects on expression levels (Asn154, Asn210) and ATP potency (Asn210).
One current goal in native mass spectrometry is the assignment of binding affinities to noncovalent complexes. Here we introduce a novel implementation of the existing laser-induced liquid bead ion desorption (LILBID) mass spectrometry method: this new method, LILBID laser dissociation curves, assesses binding strengths quantitatively. In all LILBID applications, aqueous sample droplets are irradiated by 3 µm laser pulses. Variation of the laser energy transferred to the droplet during desorption affects the degree of complex dissociation. In LILBID laser dissociation curves, laser energy transfer is purposely varied, and a binding affinity is calculated from the resulting complex dissociation. A series of dsDNAs with different binding affinities was assessed using LILBID laser dissociation curves. The binding affinity results from the LILBID laser dissociation curves strongly correlated with the melting temperatures from UV melting curves and with dissociation constants from isothermal titration calorimetry, standard solution phase methods. LILBID laser dissociation curve data also showed good reproducibility and successfully predicted the melting temperatures and dissociation constants of three DNA sequences. LILBID laser dissociation curves are a promising native mass spectrometry binding affinity method, with reduced time and sample consumption compared to melting curves or titrations.
Gephyrin is an ubiquitously expressed protein that, in the nervous system, is essential for synaptic anchoring of glycine receptors (GlyRs) and major GABAA receptor subtypes. The binding of gephyrin to the GlyR depends on an amphipathic motif within the large intracellular loop of the GlyRβ subunit. The mouse gephyrin gene consists of 30 exons. Ten of these exons, encoding cassettes of 5–40 amino acids, are subject to alternative splicing (C1–C7, C4′–C6′). Since one of the cassettes, C5′, has recently been reported to exclude GlyRs from GABAergic synapses, we investigated which cassettes are found in gephyrin associated with the GlyR. Gephyrin variants were purified from rat spinal cord, brain, and liver by binding to the glutathione S-transferase-tagged GlyRβ loop or copurified with native GlyR from spinal cord by affinity chromatography and analyzed by mass spectrometry. In addition to C2 and C6′, already known to be prominent, C4 was found to be abundant in gephyrin from all tissues examined. The nonneuronal cassette C3 was easily detected in liver but not in GlyR-associated gephyrin from spinal cord. C5 was present in brain and spinal cord polypeptides, whereas C5′ was coisolated mainly from liver. Notably C5′-containing gephyrin bound to the GlyRβ loop, inconsistent with its proposed selectivity for GABAA receptors. Our data show that GlyR-associated gephyrin, lacking C3, but enriched in C4 without C5, differs from other neuronal and nonneuronal gephyrin isoforms.
Background: In the past, protease inhibitors (PIs) and the reverse transcriptase inhibitor abacavir were identified increasing the risk for thromboembolic complications and cardiovascular events (CVE) of HIV infected patients taking a combination antiretroviral therapy (cART). Results of the previous HIV-PLA I-study lead to the assumption that platelet activation could play a substantial role in increasing CVE risks.
Methods: The open label, monocentric HIV-PLA II-study investigated HIV-1-infected, therapy-naïve adults (n=45) starting with cART, consisting either of boosted PI (atazanavir, n= 6, darunavir, n=11), NNRTI (efavirenz, n=14) or integrase inhibitor (raltegravir, n=14), each plus tenofovir/emtricitabine co-medication. Main exclusion criteria were tobacco smoking, the intake of NSAIDs or abacavir or past CVE. Platelet adhesive molecule p-selectin (CD62P) and FITC anti-human Integrin α-IIb/Integrin β-3 (CD41/CD61) antibody (PAC-1) binding, monocyte CD11b/monocyte-associated CD41 expression and the endogenous thrombin potential (ETP) were assessed ex vivo-in vitro at baseline, weeks 4, 12 and 24. Therapy regimens were blinded to the investigators for laboratory and statistical analyses.
Results: CD11b and ETP showed no significant changes or differences between all study groups. In contrast, the mean + SD mean fluorescence units (MFI) of CD62P and PAC-1 increased significantly in patients taking PI, indicating an enhanced potential for thrombocyte activation and aggregation.
Conclusion: CD62P expression, detecting the ɑ-platelet degranulation of pro-inflammatory and pro-thrombotic factors and adhesive proteins, and PAC-1 expression, representing a marker for conformation changes of the GIIb/IIIa receptor, increased significantly in patients taking HIV protease inhibitors. The findings of this study revealed a yet unknown pathway of platelet activation, possibly contributing to the increased risk for CVE under HIV protease inhibitor containing cART.
Clinical Trial Registration No.: DRKS00000288.
Oligonucleotide-based therapeutics have made rapid progress in clinical treatment of a variety of disease indications. Since most therapeutic oligonucleotides serve more than just one function and tend to have a prolonged lifetime, spatio-temporal control of these functions would be desirable. Photoswitches like azobenzene have proven themselves as useful tools in this matter. Upon irradiation, the photoisomerization of the azobenzene moiety causes destabilization in adjacent base pairs, leading to a decreased hybridization affinity. Since the way the azobenzene is incorporated in the oligonucleotide is of utmost importance, we synthesized locked azobenzene C-nucleosides and compared their photocontrol capabilities to established azobenzene C-nucleosides in oligonucleotide test-sequences by means of fluorescence-, UV/Vis-, and CD-spectroscopy.
Electronic circular dichroism unravels atropisomers of a broadly absorbing fulgide derivative
(2022)
We prepared and studied six atropisomers with different chiroptical properties emerging from a single, robust, broadly-absorbing fulgide photoswitch. After separation of the different atropisomers via HPLC on a chiral column, their isomerization processes at room temperature and the energy barriers of the different species were investigated in detail using spectroscopic and theoretical methods.
In the development of photolabile protecting groups, it is of high interest to selectively modify photochemical properties with structural changes as simple as possible. In this work, knowledge of fluorophore optimization was adopted and used to design new coumarin- based photocages. Photolysis efficiency was selectively modulated by inactivating competitive decay channels, such as twisted intramolecular charge transfer (TICT) or hydrogen-bonding, and the photolytic release of the neurotransmitter serotonin was demonstrated. Structural modifications inspired by the fluorophore ATTO 390 led to a significant increase in the uncaging cross section that can be further improved by the simple addition of a double bond. Ultrafast transient absorption spectroscopy gave insights into the underlying solvent-dependent photophysical dynamics. The chromophores presented here are excellently suited as new photocages in the visible wavelength range due to their simple synthesis and their superior photochemical properties.
We synthesized two green-light activatable 5’-caps for oligonucleotides based on the BODIPY and coumarin scaffold. Both bear an alkyne functionality allowing their use in numerous biological applications. They were successfully incorporated in oligonucleotides via solid-phase synthesis. Copper-catalyzed alkyne-azide cycloaddition (CuAAC) using a bisazide photo-tether gave cyclic oligonucleotides that could be relinearized by activation with green light and were shown to exhibit high stability against exonucleases. Chemical ligation as another example for bioconjugation yielded oligonucleotides with an internal strand break site. Irradiation at 530 nm or 565 nm resulted in complete photolysis of both caging groups.
Purpose: The quality testing and approval procedure for most pharmaceutical products is a streamlined process with standardized procedures for the determination of critical quality attributes. However, the evaluation of semisolid dosage forms for topical drug delivery remains a challenging task. The work presented here highlights confocal Raman microscopy (CRM) as a valuable tool for the characterization of such products.
Methods: CRM, a laser-based method, combining chemically-selective analysis and high resolution imaging, is used for the evaluation of different commercially available topical acyclovir creams.
Results: We show that CRM enables the spatially resolved analysis of microstructural features of semisolid products and provides insights into drug distribution and polymorphic state as well as the composition and arrangement of excipients. Further, we explore how CRM can be used to monitor phase separation and to study skin penetration and the interaction with fresh and cryopreserved excised human skin tissue.
Conclusion: This study presents a comprehensive overview and illustration of how CRM can facilitate several types of key analyses of semisolid topical formulations and of their interaction with their biological target site, illustrating that CRM is a useful tool for research, development as well as for quality testing in the pharmaceutical industry.
Non-alcoholic steatohepatitis (NASH) - a hepatic manifestation of the metabolic syndrome - is a multifactorial disease with alarming global prevalence. It involves steatosis, inflammation and fibrosis in the liver, thus demanding multiple modes of action for robust therapeutic efficacy. Aiming to fuse complementary validated anti-NASH strategies in a single molecule, we have designed and systematically optimized a scaffold for triple activation of farnesoid X receptor (FXR), peroxisome proliferator-activated receptor (PPAR) α and PPARδ. Pilot profiling of the resulting triple modulator demonstrated target engagement in native cellular settings and in mice, rendering it a suitable tool to probe the triple modulator concept in vivo. In DIO NASH in mice, the triple agonist counteracted hepatic inflammation and reversed hepatic fibrosis highlighting the potential of designed polypharmacology in NASH.
Antigen presentation via major histocompatibility complex class I (MHC I) molecules is essential to mount an adaptive immune response against pathogens and cancerous cells. To this end, the transporter associated with antigen processing (TAP) delivers snippets of the cellular proteome, resulting from proteasomal degradation, into the ER lumen. After peptide loading and editing by the peptide-loading complex (PLC), stable peptide-MHC I complexes are released for cell surface presentation. Since the process of MHC I trafficking is poorly defined, we established an approach to control antigen presentation by introduction of a photo-caged amino acid in the catalytic ATP-binding site of TAP. By optical control, we initiate TAP-dependent antigen translocation, thus providing new insights into TAP function within the PLC and MHC I trafficking in living cells. Moreover, this versatile approach has the potential to be applied in the study of other cellular pathways controlled by P-loop ATP/GTPases.
Despite all advances in drug delivery, the limitations of the analytical technologies involved in the characterization of next-generation nanomedicines are still impeding further progress of an emerging market. Discriminating between different formulations and batches, drug release is one of the most important quality criteria in development and quality control of pharmaceutics. Unfortunately, there are only few methods available to sensitively measure this important parameter for nanosized carriers. With the development of the dispersion releaser (DR) technology our group has set up a dialysis-based technique that was tested with a number of nanocarrier and nanocrystal formulations such as liposomes and polymeric nanoparticles. By supporting formulation development with a more reliable methodology to assess the drug release from nanosized carriers, a first step has been made to improve future products.
Quinone methide precursors protected with alkyldithiomethyl groups have been synthesized and converted into PNA conjugates. Stable in the absence of reducing agents, the electrophilic quinone methide is released by glutathione in concentrations typical for the cytosol. Self-alkylation then occurs or crosslinking of RNA when hybridized with complementary strands. Fastest reactions are seen for the sterically least hindered compound.
The Mycobacterium tuberculosis tyrosine-specific phosphatase MptpA and its cognate kinase PtkA are prospective targets for anti-tuberculosis drugs as they interact with the host defense response within the macrophages. Although both are structurally well-characterized, the functional mechanism regulating their activity remains poorly understood. Here, we investigate the effect of post-translational oxidation in regulating the function of MptpA. Treatment of MptpA with H2O2/NaHCO3, mimicking cellular oxidative stress conditions, leads to oxidation of the catalytic cysteine (C11) and to a conformational rearrangement of the phosphorylation loop (D-loop) by repositioning the conserved tyrosine 128 (Y128) and generating a temporarily inactive preclosed state of the phosphatase. Thus, the catalytic cysteine in the P-loop acts as a redox switch and regulates the phosphatase activity of MptpA.
The p53 protein family is the most studied protein family of all. Sequence analysis and structure determination have revealed a high
similarity of crucial domains between p53, p63 and p73. Functional studies, however, have shown a wide variety of different tasks in
tumor suppression, quality control and development. Here we review the structure and organization of the individual domains of
p63 and p73, the interaction of these domains in the context of full-length proteins and discuss the evolutionary origin of this
protein family.
FACTS:
● Distinct physiological roles/functions are performed by specific isoforms.
● The non-divided transactivation domain of p63 has a constitutively high activity while the transactivation domains of p53/p73
are divided into two subdomains that are regulated by phosphorylation.
● Mdm2 binds to all three family members but ubiquitinates only p53.
● TAp63α forms an autoinhibited dimeric state while all other vertebrate p53 family isoforms are constitutively tetrameric.
● The oligomerization domain of p63 and p73 contain an additional helix that is necessary for stabilizing the tetrameric states.
During evolution this helix got lost independently in different phylogenetic branches, while the DNA binding domain became
destabilized and the transactivation domain split into two subdomains.
OPEN QUESTIONS:
● Is the autoinhibitory mechanism of mammalian TAp63α conserved in p53 proteins of invertebrates that have the same function
of genomic quality control in germ cells?
● What is the physiological function of the p63/p73 SAM domains?
● Do the short isoforms of p63 and p73 have physiological functions?
● What are the roles of the N-terminal elongated TAp63 isoforms, TA* and GTA?
tRNAs are L-shaped RNA molecules of ~ 80 nucleotides that are responsible for decoding the mRNA and for the incorporation of the correct amino acid into the growing peptidyl-chain at the ribosome. They occur in all kingdoms of life and both their functions, and their structure are highly conserved. The L-shaped tertiary structure is based on a cloverleaf-like secondary structure that consists of four base paired stems connected by three to four loops. The anticodon base triplet, which is complementary to the sequence of the mRNA, resides in the anticodon loop whereas the amino acid is attached to the sequence CCA at the 3′-terminus of the molecule. tRNAs exhibit very stable secondary and tertiary structures and contain up to 10% modified nucleotides. However, their structure and function can also be maintained in the absence of nucleotide modifications. Here, we present the assignments of nucleobase resonances of the non-modified 77 nt tRNAIle from the gram-negative bacterium Escherichia coli. We obtained assignments for all imino resonances visible in the spectra of the tRNA as well as for additional exchangeable and non-exchangeable protons and for heteronuclei of the nucleobases. Based on these assignments we could determine the chemical shift differences between modified and non-modified tRNAIle as a first step towards the analysis of the effect of nucleotide modifications on tRNA’s structure and dynamics.
Cytochrome P450 enzymes are a large superfamily of membrane-bound heme-containing monooxygenases. They are essential for the oxidative metabolism of endogenous substrates such as steroids and fatty acids, and biotransformation of xenobiotic substrates such as pollutants and drugs. Although the highest expression of CYPs is found in the liver, their cardiovascular expression is not negligible with CYP450 subfamilies being responsible for the production of vasoactive lipids. Of importance, the enzymatic activity of all microsomal CYP450 isoenzymes is dependent on the cytochrome P450 reductase (POR), an electron donor.
In the first part of this work, the role of cytochrome P450 monooxygenases on the biotransformation of organic nitrates was investigated. Recombinant SupersomesTM were selected and incubated with NTG and PETN, where nitrite release was measured as a nitric oxide (NO) footprint. The capacity of the recombinant POR/CYP450 system to release nitrite from NO prodrugs was shown to be CYP-specific and dose-dependent. To study the involvement of CYP450 enzymes in the vascular biotransformation of organic nitrates in vivo, a smooth muscle-cell specific, inducible knockout model of POR (smcPOR-/-) was generated. Organ chamber experiments revealed that the vascular POR/CYP450 system had no impact on the dilator response of NTG and PETN. In line with previous publications, inhibition of ALDH2, known as the main enzyme responsible for the activation of NTG and PETN, and/or abolishment of the endogenous NO production did not reveal a contribution of the POR/CYP450 system to the dilator response of NTG and PETN. To better understand these results, we looked at the expression of the hepatic and vascular expression of the POR/CYP450 system where the hepatic was increased by 10- to 40-fold as shown by Western blot analysis. We concluded that due to insufficient vascular expression of CYP450 enzymes their contribution to the bioactivation of NTG and PETN is only minor.
The second part of this work focused on the cardiac relevance of endothelial isoenzymes. For that purpose, an endothelial cell-specific, tamoxifen-inducible knockout model of POR was generated and characterized in the present study. RNA-sequencing of the heart of healthy mice revealed that the CYP450 expression is cell-specific with cardiac endothelial cells (ECs) exhibiting an enrichment in the expression of the Cyp4 family (ω-oxidation of fatty acids) and of the Cyp2 family (production of EETs). Under non-stredded conditions (i.e. 30 days after inducing the knockout by tamoxifen feeding), endothelial deletion of POR was associated with cardiac remodelling as observed by an increase in the ratio of heart weight to body weight and an increase in the cardiomyocyte area. RNA-sequencing of cardiac ECs suggested that loss of POR might alter ribosomal biogenesis and protein synthesis, which could potentially affect the cardiac contractility in ecPOR-/- mice. Metabolomics from cardiac tissue of CTL and ecPOR-/- mice were not indicative for an important metabolic function of the endothelial POR/CYP450 system in the heart. The combination of transverse aortic constriction (TAC) with endothelial deletion of POR accelerates the development of heart failure in mice as detected by a reduction in cardiac output and stroke volume. These effects were mediated most likely by a reduction in vascular EETs production, which increases vascular stiffness, resulting in cardiac remodeling.
Several lines of evidence suggest the ligand-sensing transcription factor Nurr1 as a promising target to treat neurodegenerative diseases. Nurr1 modulators to validate and exploit this therapeutic potential are rare, however. To identify novel Nurr1 agonist chemotypes, we have employed the Nurr1 activator amodiaquine as template for microscale analogue library synthesis. The first set of analogues was based on the 7-chloroquiolin-4-amine core fragment of amodiaquine and revealed superior N-substituents compared to diethylaminomethylphenol contained in the template. A second library of analogues was subsequently prepared to replace the chloroquinolineamine scaffold. The two sets of analogues enabled a full scaffold hop from amodiaquine to a novel Nurr1 agonist sharing no structural features with the lead but comprising superior potency on Nurr1. Additionally, pharmacophore modeling based on the entire set of active and inactive analogues suggested key features for Nurr1 agonists.
Candida boidinii NAD+-dependent formate dehydrogenase (CbFDH) has gained significant attention for its potential applications in the production of biofuels and various industrial chemicals from inorganic carbon dioxide. The present study reports the atomic X-ray crystal structures of the wild-type CbFDH at cryogenic and ambient temperatures as well as Val120Thr mutant at cryogenic temperature determined at the Turkish Light Source "Turkish DeLight". The structures reveal new hydrogen bonds between Thr120 and water molecules in the mutant CbFDH's active site, suggesting increased stability of the active site and more efficient electron transfer during the reaction. Further experimental data is needed to test these hypotheses. Collectively, our findings provide invaluable insights into future protein engineering efforts that could potentially enhance the efficiency and effectiveness of CbFDH.
Candida boidinii NAD+-dependent formate dehydrogenase (CbFDH) has gained significant attention for its potential applications in the production of biofuels and various industrial chemicals from inorganic carbon dioxide. The present study reports the atomic X-ray crystal structures of the wild-type CbFDH at cryogenic and ambient temperatures as well as Val120Thr mutant at cryogenic temperature determined at the Turkish Light Source "Turkish DeLight". The structures reveal new hydrogen bonds between Thr120 and water molecules in the mutant CbFDH's active site, suggesting increased stability of the active site and more efficient electron transfer during the reaction. Further experimental data is needed to test these hypotheses. Collectively, our findings provide invaluable insights into future protein engineering efforts that could potentially enhance the efficiency and effectiveness of CbFDH.
BH3 mimetics are promising novel anticancer therapeutics. By selectively inhibiting BCL-2, BCL-xL, or MCL-1 (i.e. ABT-199, A-1331852, S63845) they shift the balance of pro- and anti-apoptotic proteins in favor of apoptosis. As Bromodomain and Extra Terminal (BET) protein inhibitors promote pro-apoptotic rebalancing, we evaluated the potential of the BET inhibitor JQ1 in combination with ABT-199, A-1331852 or S63845 in rhabdomyosarcoma (RMS) cells. The strongest synergistic interaction was identified for JQ1/A-1331852 and JQ1/S63845 co-treatment, which reduced cell viability and long-term clonogenic survival. Mechanistic studies revealed that JQ1 upregulated BIM and NOXA accompanied by downregulation of BCL-xL, promoting pro-apoptotic rebalancing of BCL-2 proteins. JQ1/A-1331852 and JQ1/S63845 co-treatment enhanced this pro-apoptotic rebalancing and triggered BAK- and BAX-dependent apoptosis since a) genetic silencing of BIM, BAK or BAX, b) inhibition of caspase activity with zVAD.fmk and c) overexpression of BCL-2 all rescued JQ1/A-1331852- and JQ1/S63845-induced cell death. Interestingly, NOXA played a different role in both treatments, as genetic silencing of NOXA significantly rescued from JQ1/A-1331852-mediated apoptosis but not from JQ1/S63845-mediated apoptosis. In summary, JQ1/A-1331852 and JQ1/S63845 co-treatment represent new promising therapeutic strategies to synergistically trigger mitochondrial apoptosis in RMS.
Currently, a wide variety of complex non-oral dosage forms are entering the global healthcare market. Although many assays have been described in recent research, harmonized procedures and standards for testing their in vitro performance remain widely unexplored. Among others, dialysis-based techniques such as the Pharma Test Dispersion Releaser are developed for testing the release of drugs from nanoparticles, liposomes, or extracellular vesicle preparations. Here, we provide advanced strategies and practical advice for the development and validation of dialysis-based techniques, including documentation, analysis, and interpretation of the raw data. For this purpose, key parameters of the release assay, including the hydrodynamics in the device at different stirring rates, the selectivity for particles and molecules, as well as the effect of excipients on drug permeation were investigated. At the highest stirring rate, a more than twofold increase in the membrane permeation rate (from 0.99 × 10−3 to 2.17 × 10−3 cm2/h) was observed. Additionally, we designed a novel computer model to identify important quality parameters of the dialysis experiment and to calculate error-corrected release profiles. Two hydrophilic creams of diclofenac, Voltaren® Emulgel, and Olfen® gel, were tested and provide first-hand evidence of the robustness of the assay in the presence of semisolid dosage forms.
During evolution of an RNA world, the development of enzymatic function was essential. Such enzymatic function was linked to RNA sequences capable of adopting specific RNA folds that possess catalytic pockets to promote catalysis. Within this primordial RNA world, initially evolved self-replicating ribozymes presumably mutated to ribozymes with new functions. Schultes and Bartel (Science 2000, 289, 448–452) investigated such conversion from one ribozyme to a new ribozyme with distinctly different catalytic functions. Within a neutral network that linked these two prototype ribozymes, a single RNA chain could be identified that exhibited both enzymatic functions. As commented by Schultes and Bartel, this system possessing one sequence with two enzymatic functions serves as a paradigm for an evolutionary system that allows neutral drifts by stepwise mutation from one ribozyme into a different ribozyme without loss of intermittent function. Here, we investigated this complex functional diversification of ancestral ribozymes by analyzing several RNA sequences within this neutral network between two ribozymes with class III ligase activity and with self-cleavage reactivity. We utilized rapid RNA sample preparation for NMR spectroscopic studies together with SHAPE analysis and in-line probing to characterize secondary structure changes within the neutral network. Our investigations allowed delineation of the secondary structure space and by comparison with the previously determined catalytic function allowed correlation of the structure-function relation of ribozyme function in this neutral network.
Polo-like kinase 1 (PLK1) is a crucial regulator of cell cycle progression. It is established that the activation of PLK1 depends on the coordinated action of Aurora-A and Bora. Nevertheless, very little is known about the spatiotemporal regulation of PLK1 during G2, specifically, the mechanisms that keep cytoplasmic PLK1 inactive until shortly before mitosis onset. Here, we describe PLK1 dimerization as a new mechanism that controls PLK1 activation. During the early G2 phase, Bora supports transient PLK1 dimerization, thus fine-tuning the timely regulated activation of PLK1 and modulating its nuclear entry. At late G2, the phosphorylation of T210 by Aurora-A triggers dimer dissociation and generates active PLK1 monomers that support entry into mitosis. Interfering with this critical PLK1 dimer/monomer switch prevents the association of PLK1 with importins, limiting its nuclear shuttling, and causes nuclear PLK1 mislocalization during the G2-M transition. Our results suggest a novel conformational space for the design of a new generation of PLK1 inhibitors.
Multiple resistance and pH adaptation (Mrp) cation/proton antiporters are essential for growth of a variety of halophilic and alkaliphilic bacteria under stress conditions. Mrp-type antiporters are closely related to the membrane domain of respiratory complex I. We determined the structure of the Mrp antiporter from Bacillus pseudofirmus by electron cryo-microscopy at 2.2 Å resolution. The structure resolves more than 99% of the sidechains of the seven membrane subunits MrpA to MrpG plus 360 water molecules, including ~70 in putative ion translocation pathways. Molecular dynamics simulations based on the high-resolution structure revealed details of the antiport mechanism. We find that switching the position of a histidine residue between three hydrated pathways in the MrpA subunit is critical for proton transfer that drives gated trans-membrane sodium translocation. Several lines of evidence indicate that the same histidine-switch mechanism operates in respiratory complex I.
Multiple resistance and pH adaptation (Mrp) cation/proton antiporters are essential for growth of a variety of halophilic and alkaliphilic bacteria under stress conditions. Mrp-type antiporters are closely related to the membrane domain of respiratory complex I. We determined the structure of the Mrp antiporter from Bacillus pseudofirmus by electron cryo-microscopy at 2.2 Å resolution. The structure resolves more than 99% of the sidechains of the seven membrane subunits MrpA to MrpG plus 360 water molecules, including ∼70 in putative ion translocation pathways. Molecular dynamics simulations based on the high-resolution structure revealed details of the antiport mechanism. We find that switching the position of a histidine residue between three hydrated pathways in the MrpA subunit is critical for proton transfer that drives gated transmembrane sodium translocation. Several lines of evidence indicate that the same histidine-switch mechanism operates in respiratory complex I.
Transfer RNA fragments replace microRNA regulators of the cholinergic post-stroke immune blockade
(2020)
Stroke is a leading cause of death and disability. Recovery depends on a delicate balance between inflammatory responses and immune suppression, tipping the scale between brain protection and susceptibility to infection. Peripheral cholinergic blockade of immune reactions fine-tunes this immune response, but its molecular regulators are unknown. Here, we report a regulatory shift in small RNA types in patient blood sequenced two days after ischemic stroke, comprising massive decreases of microRNA levels and concomitant increases of transfer RNA fragments (tRFs) targeting cholinergic transcripts. Electrophoresis-based size-selection followed by RT-qPCR validated the top 6 upregulated tRFs in a separate cohort of stroke patients, and independent datasets of small and long RNA sequencing pinpointed immune cell subsets pivotal to these responses, implicating CD14+ monocytes in the cholinergic inflammatory reflex. In-depth small RNA targeting analyses revealed the most-perturbed pathways following stroke and implied a structural dichotomy between microRNA and tRF target sets. Furthermore, lipopolysaccharide stimulation of murine RAW 264.7 cells and human CD14+ monocytes upregulated the top 6 stroke-perturbed tRFs, and overexpression of stroke-inducible tRF-22-WE8SPOX52 using an ssRNA mimic induced downregulation of immune regulator Z-DNA binding protein 1 (Zbp1). In summary, we identified a “changing of the guards” between RNA types that may systemically affect homeostasis in post-stroke immune responses, and pinpointed multiple affected pathways, which opens new venues for establishing therapeutics and biomarkers at the protein- and RNA-level.
Significance Statement Ischemic stroke triggers peripheral immunosuppression, increasing the susceptibility to post-stroke pneumonia that is linked with poor survival. The post-stroke brain initiates intensive communication with the immune system, and acetylcholine contributes to these messages; but the responsible molecules are yet unknown. We discovered a “changing of the guards,” where microRNA levels decreased but small transfer RNA fragments (tRFs) increased in post-stroke blood. This molecular switch may re-balance acetylcholine signaling in CD14+ monocytes by regulating their gene expression and modulating post-stroke immunity. Our observations point out to tRFs as molecular regulators of post-stroke immune responses that may be potential therapeutic targets.
Transfer RNA fragments replace microRNA regulators of the cholinergic post-stroke immune blockade
(2020)
Stroke is a leading cause of death and disability. Recovery depends on balance between inflammatory response and immune suppression, which can be CNS-protective but may worsen prognosis by increasing patients’ susceptibility to infections. Peripheral cholinergic blockade of immune reactions fine-tunes this immune response, but its molecular regulators are unknown. Therefore, we sought small RNA balancers of the cholinergic anti-inflammatory pathway in peripheral blood from ischemic stroke patients. Using RNA-sequencing and RT-qPCR, we discovered in patients’ blood on day 2 after stroke a “change of guards” reflected in massive decreases in microRNAs (miRs) and increases in transfer RNA fragments (tRFs) targeting cholinergic transcripts. Electrophoresis-based size-selection followed by RT-qPCR validated the top 6 upregulated tRFs in a separate cohort of stroke patients, and independent small RNA-sequencing datasets presented post-stroke enriched tRFs as originating from lymphocytes and monocytes. In these immune compartments, we found CD14+ monocytes to express the highest amounts of cholinergic transcripts. In-depth analysis of CD14+ regulatory circuits revealed minimally overlapping subsets of transcription factors carrying complementary motifs to miRs or tRFs, indicating different roles for the stroke-perturbed members of these small RNA species. Furthermore, LPS-stimulated murine RAW264.7 cells presented dexamethasone-suppressible upregulation of the top 6 tRFs identified in human patients, indicating an evolutionarily conserved and pharmaceutically treatable tRF response to inflammatory cues. Our findings identify tRF/miR subgroups which may co-modulate the homeostatic response to stroke in patients’ blood and open novel venues for establishing RNA-targeted concepts for post-stroke diagnosis and therapeutics.
Transfer RNA fragments replace microRNA regulators of the cholinergic poststroke immune blockade
(2020)
Stroke is a leading cause of death and disability. Recovery depends on a delicate balance between inflammatory responses and immune suppression, tipping the scale between brain protection and susceptibility to infection. Peripheral cholinergic blockade of immune reactions fine-tunes this immune response, but its molecular regulators are unknown. Here, we report a regulatory shift in small RNA types in patient blood sequenced 2 d after ischemic stroke, comprising massive decreases of microRNA levels and concomitant increases of transfer RNA fragments (tRFs) targeting cholinergic transcripts. Electrophoresis-based size-selection followed by qRT-PCR validated the top six up-regulated tRFs in a separate cohort of stroke patients, and independent datasets of small and long RNA sequencing pinpointed immune cell subsets pivotal to these responses, implicating CD14+ monocytes in the cholinergic inflammatory reflex. In-depth small RNA targeting analyses revealed the most-perturbed pathways following stroke and implied a structural dichotomy between microRNA and tRF target sets. Furthermore, lipopolysaccharide stimulation of murine RAW 264.7 cells and human CD14+ monocytes up-regulated the top six stroke-perturbed tRFs, and overexpression of stroke-inducible tRF-22-WE8SPOX52 using a single-stranded RNA mimic induced down-regulation of immune regulator Z-DNA binding protein 1. In summary, we identified a “changing of the guards” between small RNA types that may systemically affect homeostasis in poststroke immune responses, and pinpointed multiple affected pathways, which opens new venues for establishing therapeutics and biomarkers at the protein and RNA level.
Nanoarzneimittel haben in den letzten Jahren in der Therapie verschiedener Erkrankungen immer mehr an Bedeutung gewonnen. Dadurch hat auch die Anzahl zugelassener Arzneimittel mit an Arzneistoffträgern wie Liposomen gebundenen Wirkstoffen zugenommen. Weil für die Zulassung, neben der Wirksamkeit und Unbedenklichkeit, auch die Qualität der neuen Arzneimittel gewährleistet sein muss, spielen die verschiedenen Eigenschaften der Arzneistoffträger eine wichtige Rolle in der Qualitätskontrolle. Neben der Partikelgröße, der Partikelgrößenverteilung und der Oberflächenladung spielt die (Rest-)Kristallinität des Wirkstoffs und die Wirkstofffreisetzung eine wesentliche Rolle für die erfolgreiche in vivo-Performance von Nanoarzneimitteln. Zur Bestimmung der Wirkstofffreisetzung aus kolloidalen Arzneistoffträgern wie Liposomen, Nanopartikeln oder Mizellen gibt es bis heute keine Standardmethoden. In der Forschung und der pharmazeutischen Industrie werden folglich verschiedene Methoden wie Filtration, Zentrifugation oder Dialyse verwendet, um den freigesetzten Wirkstoff zu bestimmen. Dabei ist die Wahl der Separationsmethode auf die Eigenschaften der Arzneistoffträger abzustimmen.
In der vorliegenden Arbeit wurde eine dialysebasierte Apparatur, der Dispersion Releaser (DR), zur Untersuchung der in vitro Wirkstofffreisetzung aus kolloidalen Trägersystemen eingesetzt. Diese kann direkt mit den Apparaturen I/II der Arzneibücher der Europäischen Union (Ph. Eur.) und der Vereinigten Staaten (USP) gekoppelt werden. Zur Untersuchung der Wirkstofffreisetzung wird die Formulierung in das Donorkompartiment gegeben, sodass der freigesetzte Wirkstoff infolge über die Dialysemembran in das Akzeptorkompartiment permeiert. Dort kann dieser mittels HPLC analysiert werden. Besonders hervorzuheben ist das synchrone Rühren in beiden Kompartimenten des DR, worüber andere dialysebasierte Apparaturen nicht verfügen.
Die Entwicklung und Patentierung eines funktionsfähigen Prototyps des DR erfolgte an der Goethe Universität, Frankfurt am Main und wurde im Rahmen dieser Arbeit gemeinsam mit der Pharma Test Apparatebau AG (Hainburg, Deutschland) zu einer kommerziell erwerbbaren Apparatur (Pharma Test Dispersion Releaser, PTDR) weiterentwickelt. Innerhalb dieser Kollaboration wurde der Prototyp des DR unter Einbezug der Anforderungen der pharmazeutischen Industrie rekonstruiert. Eine erleichterte Anwendung für den Nutzer wurde dabei mitberücksichtigt.
Die finale Apparatur wurde zuletzt einer ausgiebigen Validierung unterzogen, bei der Diclofenac und Hydrocortison als Modellarzneistoffe dienten. Neben Untersuchungen zur Hydrodynamik und dem Einfluss der Umdrehungszahl auf die Membranpermeationsrate kM wurde eine Methode mit Gold-Nanopartikeln zur Bestimmung der Dichtigkeit des Systems entwickelt. Hierbei wurden Messungen mit einer UV/Vis-Methode und mit dynamischer Lichtstreuung durchgeführt, um die Abwesenheit der Goldpartikel im Akzeptorkompartiment nachzuweisen. Der Einfluss von Proteinen im Freisetzungsmedium auf die Membran-permeation wurde ebenfalls untersucht.
Der DR wurde ursprünglich zur Untersuchung von parenteralen Nanoformulierungen entwickelt. Aufgrund der bisher noch nicht erfolgten Untersuchung von halbfesten Zubereitungen im DR, wurde die Apparatur im Rahmen dieser Forschungsarbeit für zwei verschiedene Diclofenac-Gele (Voltaren® Emulgel, Olfen® Gel) unter verschiedenen Bedingungen evaluiert. Dabei konnte unter non-sink-Bedingungen der Einfluss der lipophilen Phase des Voltaren® Emulgels (GlaxoSmithKline Consumer Healthcare GmbH & Co. KG, München, Deutschland) gezeigt werden. Im Vergleich zum fettfreien Olfen® Gel (Mepha Pharma AG, Basel, Schweiz) zeigte Voltaren® Emulgel eine vollständige Freisetzung unter den erschwerten Löslichkeitsbedingungen.
Mit Hydrocortison als Modellsubstanz wurden vier verschiedene Proliposomen zur vaginalen An¬wendung formuliert. Neben der Charakterisierung der Partikelgröße und der Verkapselungs¬effizienz wurden Messungen mit dynamischer Differenzkalorimetrie durch-geführt und Aufnahmen zur morphologischen Charakterisierung mittels Transmissions-elektronen¬mikroskopie der Liposomen erstellt. Die Wirkstofffreisetzung des Hydrocortisons aus dem rekonstituierten liposomalen Gel sowie die Permeabilität über eine Zellmonoschicht wurde vergleichend untersucht. Dabei wurden Zelllinien aus humanem Cervixkarzinom beziehungsweise Endometriumkarzinom eingesetzt. Die Unterschiede der Formulierungen konnten vom DR sensitiver erfasst werden und die Verkapselungseffizienz als relevanter Faktor für die in vivo-Performance festgelegt werden.
Weil die tatsächliche Wirkstofffreisetzung durch die Permeation über die Dialysemembran überlagert werden kann, wurde neben der Standardisierung der Konstruktion die Auswertung mit Hilfe eines neuen mathematischen Modells, das auf dem Fick’schen Diffusionsgesetz basiert, verbessert. Das Normalisieren des Freisetzungsprofils mit Hilfe des mathematischen Modells dient dazu, die tatsächliche Wirkstofffreisetzung zu berechnen und den Vergleich verschiedener Freisetzungen ohne den Einfluss der Membranpermeation zu ermöglichen. Im Zuge der Validierung des DR wurde das mathematische Modell ebenfalls erfolgreich validiert.
In der vorliegenden Forschungsarbeit wurde eine neue Konstruktion des DR für die kommerzielle Anwendung entwickelt und validiert. Nebenbei wurde der Auswerteprozess zur Berechnung der diffusionsbereinigten Wirkstofffreisetzung vereinheitlicht und validiert. Zuletzt wurde das Anwendungsgebiet des DR von parenteralen Nanoformulierungen auf halbfeste Arzneiformen erweitert.
Alzheimer’s disease (AD) is the most prevalent neurodegenerative disease causing dementia and poses significant health risks to middle-aged and elderly people. Brain magnetic resonance imaging (MRI) is the most widely used diagnostic method for AD. However, it is challenging to collect sufficient brain imaging data with high-quality annotations. Weakly supervised learning (WSL) is a machine learning technique aimed at learning effective feature representation from limited or low-quality annotations. In this paper, we propose a WSL-based deep learning (DL) framework (ADGNET) consisting of a backbone network with an attention mechanism and a task network for simultaneous image classification and image reconstruction to identify and classify AD using limited annotations. The ADGNET achieves excellent performance based on six evaluation metrics (Kappa, sensitivity, specificity, precision, accuracy, F1-score) on two brain MRI datasets (2D MRI and 3D MRI data) using fine-tuning with only 20% of the labels from both datasets. The ADGNET has an F1-score of 99.61% and sensitivity is 99.69%, outperforming two state-of-the-art models (ResNext WSL and SimCLR). The proposed method represents a potential WSL-based computer-aided diagnosis method for AD in clinical practice.
The prevention of tau protein aggregations is a therapeutic goal for the treatment of Alzheimer's disease (AD), and hydromethylthionine (HMT) (also known as leucomethylthioninium-mesylate [LMTM]), is a potent inhibitor of tau aggregation in vitro and in vivo. In two Phase 3 clinical trials in AD, HMT had greater pharmacological activity on clinical endpoints in patients not receiving approved symptomatic treatments for AD (acetylcholinesterase (AChE) inhibitors and/or memantine) despite different mechanisms of action. To investigate this drug interaction in an animal model, we used tau-transgenic L1 and wild-type NMRI mice treated with rivastigmine or memantine prior to adding HMT, and measured changes in hippocampal acetylcholine (ACh) by microdialysis. HMT given alone doubled hippocampal ACh levels in both mouse lines and increased stimulated ACh release induced by exploration of the open field or by infusion of scopolamine. Rivastigmine increased ACh release in both mouse lines, whereas memantine was more active in tau-transgenic L1 mice. Importantly, our study revealed a negative interaction between HMT and symptomatic AD drugs: the HMT effect was completely eliminated in mice that had been pre-treated with either rivastigmine or memantine. Rivastigmine was found to inhibit AChE, whereas HMT and memantine had no effects on AChE or on choline acetyltransferase (ChAT). The interactions observed in this study demonstrate that HMT enhances cholinergic activity in mouse brain by a mechanism of action unrelated to AChE inhibition. Our findings establish that the drug interaction that was first observed clinically has a neuropharmacological basis and is not restricted to animals with tau aggregation pathology. Given the importance of the cholinergic system for memory function, the potential for commonly used AD drugs to interfere with the treatment effects of disease-modifying drugs needs to be taken into account in the design of clinical trials.
Riboswitches are regulatory RNA elements that undergo functionally important allosteric conformational switching upon binding of specific ligands. The here investigated guanidine-II riboswitch binds the small cation, guanidinium, and forms a kissing loop-loop interaction between its P1 and P2 hairpins. We investigated the structural changes to support previous studies regarding the binding mechanism. Using NMR spectroscopy, we confirmed the structure as observed in crystal structures and we characterized the kissing loop interaction upon addition of Mg2+ and ligand for the riboswitch aptamer from Escherichia coli. We further investigated closely related mutant constructs providing further insight into functional differences between the two (different) hairpins P1 and P2. Formation of intermolecular interactions were probed by small-angle X-ray scattering (SAXS) and NMR DOSY data. All data are consistent and show the formation of oligomeric states of the riboswitch induced by Mg2+ and ligand binding.
Im Rahmen dieser Arbeit wurde die schnelle Energietransfer- (EET) und Elektronentransfer (ET)-Dynamik unterschiedlichster Quantenpunkte (QD) spektroskopisch untersucht. Die untersuchten Systeme bestanden in den meisten Fällen aus Donor-Akzeptor-Paaren, bei denen die Halbleiternanokristalle als Donor fungierten. Der Fokus lag dabei auf der gezielten Anpassung des Donors, um die optimale Funktionalität zu erreichen. Die Untersuchung der Nanokristalle erstreckte sich daher von einfachen Kernen über verschiedene Kern-Schale-Partikel bis hin zu völlig anderen Strukturen wie Nanoplatelets (NPL). Als Akzeptor wurden eine Vielzahl von Molekülen verwendet, die sich als Elektronen- und/oder Energieakzeptoren für die verschiedenen QDs eignen.
1H, 13C and 15N chemical shift assignment of the stem-loops 5b + c from the 5′-UTR of SARS-CoV-2
(2022)
The ongoing pandemic of the respiratory disease COVID-19 is caused by the SARS-CoV-2 (SCoV2) virus. SCoV2 is a member of the Betacoronavirus genus. The 30 kb positive sense, single stranded RNA genome of SCoV2 features 5′- and 3′-genomic ends that are highly conserved among Betacoronaviruses. These genomic ends contain structured cis-acting RNA elements, which are involved in the regulation of viral replication and translation. Structural information about these potential antiviral drug targets supports the development of novel classes of therapeutics against COVID-19. The highly conserved branched stem-loop 5 (SL5) found within the 5′-untranslated region (5′-UTR) consists of a basal stem and three stem-loops, namely SL5a, SL5b and SL5c. Both, SL5a and SL5b feature a 5′-UUUCGU-3′ hexaloop that is also found among Alphacoronaviruses. Here, we report the extensive 1H, 13C and 15N resonance assignment of the 37 nucleotides (nts) long sequence spanning SL5b and SL5c (SL5b + c), as basis for further in-depth structural studies by solution NMR spectroscopy.
The formation of amyloid-β oligomers plays a key role in the onset of Alzheimer’s disease. We investigated the aggregation of amyloid-β oligomers by mass spectrometry and ion mobility spectrometry, revealing those structural properties, which lead to the formation of mature fibrils. We can show that the arrangement of the first oligomers is crucial for the topology of the resulting species, leading to the formation of non-toxic aggregates or fibrils.
Herein, we present a multi-cycle chemoenzymatic synthesis of modified RNA with simplified solid-phase handling to overcome size limitations of RNA synthesis. It combines the advantages of classical chemical solid-phase synthesis and enzymatic synthesis using magnetic streptavidin beads and biotinylated RNA. Successful introduction of light-controllable RNA nucleotides into the tRNAMet sequence was confirmed by gel electrophoresis and mass spectrometry. The methods tolerate modifications in the RNA phosphodiester backbone and allow introductions of photocaged and photoswitchable nucleotides as well as photocleavable strand breaks and fluorophores.
The heterotetrameric human transfer RNA (tRNA) splicing endonuclease (TSEN) catalyzes the excision of intronic sequences from precursor tRNAs (pre-tRNAs)1. Mutations in TSEN and its associated RNA kinase CLP1 are linked to the neurodegenerative disease pontocerebellar hypoplasia (PCH)2–8. The three-dimensional (3D) assembly of TSEN/CLP1, the mechanism of substrate recognition, and the molecular details of PCH-associated mutations are not fully understood. Here, we present cryo-electron microscopy structures of human TSEN with intron-containing pre-tRNATyrgta and pre-tRNAArgtct. TSEN exhibits broad structural homology to archaeal endonucleases9 but has evolved additional regulatory elements that are involved in handling and positioning substrate RNA. Essential catalytic residues of subunit TSEN34 are organized for the 3’ splice site which emerges from a bulge-helix configuration. The triple-nucleotide bulge at the intron/3’-exon boundary is stabilized by an arginine tweezer motif of TSEN2 and an interaction with the proximal minor groove of the helix. TSEN34 and TSEN54 define the 3’ splice site by holding the tRNA body in place. TSEN54 adapts a bipartite fold with a flexible central region required for CLP1 binding. PCH-associated mutations are located far from pre-tRNA binding interfaces explaining their negative impact on structural integrity of TSEN without abrogating its catalytic activity in vitro10. Our work defines the molecular framework of pre-tRNA recognition and cleavage by TSEN and provides a structural basis to better understand PCH in the future.
Structure-function relationships in substrate binding protein dependent secondary transporters
(2023)
This work provides new insights into the relevance of SBP dependent secondary transport systems, especially in the thus far under-researched subgroup of TAXI transporters. Importantly, we identified and characterized the TAXI transport system TAXIPm-PQM from Proteus mirabilis. We demonstrated that, in contrast to previously characterized SBP dependent secondary transport systems, TAXIPm-PQM is a proton coupled system and transports the C5-dicarboxylate α- ketoglutarate. Since initially the transport of α-ketoglutarate could only be demonstrated in vivo but not in vitro using established protocols (Mulligan et al. 2009), we investigated in detail the differences between the in vivo and in vitro assay. This resulted in a bioinformatic analysis of TRAP and TAXI signal peptides, which strongly implied that TAXIPm-P requires a transmembrane anchor to allow for transport. We then provided TAXIPm-P surface tethered to the membrane in in vitro transport assays and confirmed the prediction of our bioinformatic analysis that TAXIPm-PQM deploys a membrane-anchored instead of a soluble SBP. Furthermore, the TAXI transport system TAXIMh-PQM from Marinobacter hydrocarbonoclasticus transports fumarate only if both membrane domains Q and M are present. For further characterization, Michaelis-Menten kinetics and affinities were determined for both TAXI transport systems TAXIPm-PQM from Proteus mirabilis and TAXIMh-PQM from Marinobacter hydrocarbonoclasticus. In addition, nanobodies were selected for the membrane domain TAXIPm-QM from Proteus mirabilis to stabilize different conformations which can serve in subsequent structural elucidation studies. Furthermore, the TRAP SBP TRAPHi-SiaP from Haemophilus influenzae was shown to interact not only with its corresponding membrane domain TRAPHi-SiaQM but with at least one additional transporter. It was thereby excluded that TRAPHi- SiaP transfers N-acetylneuraminic acid to the only native E. coli TRAP transporter TRAPEc-YiaMNO and suggested to rather interact with a SBP dependent ABC transport system as this protein family represents the largest SBP dependent protein group in E. coli (Moussatova et al. 2008).
Salt-inducible kinases (SIKs) are key metabolic regulators. Imbalance of SIK function is associated with the development of diverse cancers, including breast, gastric and ovarian cancer. Chemical tools to clarify the roles of SIK in different diseases are, however, sparse and are generally characterized by poor kinome-wide selectivity. Here, we have adapted the pyrido[2,3-d]pyrimidin-7-one-based PAK inhibitor G-5555 for the targeting of SIK, by exploiting differences in the back-pocket region of these kinases. Optimization was supported by high-resolution crystal structures of G-5555 bound to the known off-targets MST3 and MST4, leading to a chemical probe, MRIA9, with dual SIK/PAK activity and excellent selectivity over other kinases. Furthermore, we show that MRIA9 sensitizes ovarian cancer cells to treatment with the mitotic agent paclitaxel, confirming earlier data from genetic knockdown studies and suggesting a combination therapy with SIK inhibitors and paclitaxel for the treatment of paclitaxel-resistant ovarian cancer.
Unc-51-like kinase 4 (ULK4) is a pseudokinase that has been linked to the development of several diseases. Even though sequence motifs required for ATP binding in kinases are lacking, ULK4 still tightly binds ATP and the presence of the cofactor is required for structural stability of ULK4. Here we present a high-resolution structure of a ULK4-ATPγS complex revealing a highly unusual ATP binding mode in which the lack of the canonical VAIK motif lysine is compensated by K39, located N-terminal to αC. Evolutionary analysis suggests that degradation of active site motifs in metazoan ULK4 has co-occurred with an ULK4 specific activation loop, which stabilizes the C-helix. In addition, cellular interaction studies using BioID and biochemical validation data revealed high confidence interactors of the pseudokinase and armadillo repeat domains. Many of the identified ULK4 interaction partners were centrosomal and tubulin associated proteins and several active kinases suggesting new roles for ULK4.
Highlights: Structure of the ULK4 ATP complex reveals a unique ATP binding mode.
Disease associated mutations modulate ATP binding and ULK4 stability
Degradation of active site motifs co-occurred in evolution with an ULK4 specific activation loop
BioID suggests a role of ULK4 regulating centrosomal and cytoskeletal functions,
MKK7 (MEK7) is a key regulator of the JNK stress signaling pathway and targeting MKK7 has been proposed as a chemotherapeutic strategy. Detailed understanding of the MKK7 structure and factors that impact its activity is therefore of critical importance. Here, we present a comprehensive set of MKK7 crystal structures revealing insights into catalytic domain plasticity and the role of the N-terminal regulatory helix, conserved in all MAP2Ks, mediating kinase activation. Crystal structures harboring this regulatory helix revealed typical structural features of active kinase, providing exclusively a first model of the MAP2K active state. A small molecule screening campaign yielded multiple scaffolds, including type-II irreversible inhibitors a binding mode that has not been reported previously. We also observed an unprecedented allosteric pocket located in the N-terminal lobe for the approved drug ibrutinib. Collectively, our structural and functional data expand and provide alternative targeting strategies for this important MAP2K kinase.
Selectivity remains a challenge for ATP-mimetic kinase inhibitors, an issue that may be overcome by targeting unique residues or binding pockets. However, to date only few strategies have been developed. Here we identify that bulky residues located N-terminal to the DFG motif (DFG-1) represent an opportunity for designing highly selective inhibitors with unexpected binding modes. We demonstrate that several diverse inhibitors exerted selective, noncanonical binding modes that exclusively target large hydrophobic DFG-1 residues present in many kinases including PIM, CK1, DAPK, and CLK. By use of the CLK family as a model, structural and biochemical data revealed that the DFG-1 valine controlled a noncanonical binding mode in CLK1, providing a rationale for selectivity over the closely related CLK3 which harbors a smaller DFG-1 alanine. Our data suggest that targeting the restricted back pocket in the small fraction of kinases that harbor bulky DFG-1 residues offers a versatile selectivity filter for inhibitor design.
Selectivity remains a challenge for ATP-mimetic kinase inhibitors, an issue that may be overcome by targeting unique residues or binding pockets. However, to date only few strategies have been developed. Here we identify that bulky residues located N-terminal to the DFG motif (DFG-1) represent an opportunity for designing highly selective inhibitors with unexpected binding modes. We demonstrate that several diverse inhibitors exerted selective, non-canonical binding modes that exclusively target large hydrophobic DFG-1 residues present in many kinases including PIM, CK1, DAPK and CLK. Using the CLK family as a model, structural and biochemical data revealed that the DFG-1 valine controlled a non-canonical binding mode in CLK1, providing a rational for selectivity over the closely-related CLK3 which harbors a smaller DFG-1 alanine. Our data suggests that targeting the restricted back pocket in the small fraction of kinases that harbor bulky DFG-1 residues offers a versatile selectivity filter for inhibitor design.
The nsP3 macrodomain is a conserved protein interaction module that plays essential regulatory roles in host immune response by recognizing and removing posttranslational ADP-ribosylation sites during SARS-CoV-2 infection. Thus, targeting this protein domain may offer a therapeutic strategy to combat the current and future virus pandemics. To assist inhibitor development efforts, we report here a comprehensive set of macrodomain crystal structures complexed with diverse naturally-occurring nucleotides, small molecules as well as nucleotide analogues including GS-441524 and its phosphorylated analogue, active metabolites of remdesivir. The presented data strengthen our understanding of the SARS-CoV-2 macrodomain structural plasticity and it provides chemical starting points for future inhibitor development.
DNA points accumulation for imaging in nanoscale topography (DNA-PAINT) is a super-resolution technique with relatively easy-to-implement multi-target imaging. However, image acquisition is slow as sufficient statistical data has to be generated from spatio-temporally isolated single emitters. Here, we train the neural network (NN) DeepSTORM to predict fluorophore positions from high emitter density DNA-PAINT data. This achieves image acquisition in one minute. We demonstrate multi-colour super-resolution imaging of structure-conserved semi-thin neuronal tissue and imaging of large samples. This improvement can be integrated into any single-molecule imaging modality to enable fast single-molecule super-resolution microscopy.
N6-methyladenosine (m6A) is the most abundant and well understood modification in eukaryotic mRNA and was first identified in polyadenylated parts of the mRNA.The distinct distribution of m6A in the transcriptome with special enrichment in long internal exons, 39UTRs and around stop codons was uncovered by early biochemical work and later on antibody based sequencing techniques. The so called m6A writer, reader and eraser machinery is responsible for the dynamic and with that regulatory nature of the m6A modification. As m6A writer, the human N6-methyltransferase complex (MTC) cotranscriptionally methylates the central adenine within a RRACH (preferably GGACU) sequence context to form m6A in the nascent RNA chain.9–15 The catalytic core of the complex is formed by the two proteins METTL3 and METTL14, with the active site located in the methyltransferase domain (MTD) of METTL3.16–18 The DPPW motif near the methyl donor S-adenosylmethionine (SAM) binding site in this MTD was postulated to bind the target adenine during catalysis. Moreover, a positively charged groove in the METTL3-METTL14 interface, the C-terminal RGG domain in METTL14 and the zinc finger motifs in METTL3 were identified as important domains for RNA binding. However, to date there are no full-length or substrate-RNA-bound structures of the catalytic METTL3-METTL14 complex.
In addition, a set of accessory proteins assembles to the METTL3-METTL14 heterodimer to form the full MTC, mediated by WTAP that firmly binds to the N-terminal leader helix in METTL3.20 WTAP was shown to locate the whole complex to the nuclear speckles and can modulate m6A deposition to specific sites in the RNA. Moreover, WTAP acts as binding platform for other accessory proteins including VIRMA, RBM15, ZC3H13 and HAKAI that are mostly identified to mediate position specific methylation. For example, RBM15 was shown to mediates region-selective methylation in a WTAP dependent manner, directing specificity towards U-rich sequences.
The observed specificity of the methyltransferase complex to methylate only site specific DRACH sequenced is still poorly understood. Some possible modulators like the role of the accessory proteins are under investigation, however, the structural context of the RNA methylation sites or a structural preference of the complex have been mainly neglected so far. Moreover, the structural dynamics of this methylation process still remain elusive. This thesis contributes to the afore-mentioned aspects by analysis of the methylation process regarding RNA structure sensitivity with enzymatic activity assays and its dynamic nature by implementing a smFRET approach.
We hypothesized the target RNA secondary structure to be an additional important modulator of methylation efficiency, based on the RNA binding elements of the complex (positively charged binding groove, zinc finger domain, RGG domain) and the supposed target adenine binding in the active site. Here, we postulated the possibility for a flipped-out adenine to be of special relevance, which is closely related to the local stability of the target adenine containing structure. Moreover, efficient binding of the protein complex to the RNA should require the ability to anchor the RNA on both sides of the target sequence.
Large international airports were identified as sources of ultrafine particles (UFPs) (Hu et al., 2009; Yu et al., 2012; Hsu et al., 2013; Keuken et al., 2015; Hudda and Fruin, 2016). Since September 2017 UFP emissions originating from the Frankfurt International Airport, Germany are monitored by the Hessian Agency for Nature Conservation, Environment and Geology (HLNUG) showing elevated UFP concentrations during airport operating hours (05:00–23:00 CET) (Ditas et al., 2022). Referring to that, the organic chemical composition of aviation-related UFPs emerging from the Frankfurt Airport was analysed by performing a comprehensive non-target screening of UFP filter samples.
Aluminium-filter samples were collected at an air quality monitoring station 4 km north of the Frankfurt Airport, using a 13-stage impactor system (Nano-MOUDI). The chemical
characterization of UFPs in the size range of 10-18 nm, 18-32 nm and 32-56 nm was accomplished by ultra-high-performance liquid chromatography, heated electrospray ionisation and mass analysis using an Orbitrap high-resolution mass spectrometer. Non-target screening revealed that the majority of detected compounds belong to homologous series of two different types of organic esters, which are base stocks of aircraft lubrication oils.
In reference to five different jet engine lubrication oils of various manufacturers, the corresponding lubricant base stocks and their additives, two amines and one organophosphate, were identified in the UFPs by the use of matching retention time, exact mass and MS/MS fragmentation pattern of single organic molecules. The quantitative analysis of the jet engine oil constituents in the aviation-related UFPs with diameters < 56 nm was accomplished by standard addition. By characterizing the Nano-MOUDI, loss factors for each size stage were determined and used for correction accordingly. Particle-number size distribution measurements, conducted parallel to the filter sampling, enabled the determination of the jet engine oil contribution to the UFP mass.
Furthermore, the nucleation and particle formation potential of a commonly used synthetic jet engine lubrication oil was investigated in the laboratory. Thermodenuder experiments at 20 °C and 300 °C were carried out to monitor the gas-to-particle partitioning behaviour of jet engine oils. At 300 °C a significantly higher number of particles with a mean diameter of ~10 nm are formed, leading to a more than fivefold increase in total particle numbers compared to 20 °C. Particle diameters of the newly formed oil particles in the laboratory experiment appeared in the same size region as UFPs emerging from Frankfurt Airport. Particles originating from the Frankfurt city centre direction showed larger diameters.
Results indicate that aircraft emissions strongly influence the total mass of 10-18 nm particles. The jet oil fraction decreases for bigger particles (e.g., 18-56 nm), implying that these oils form new particles in the cooling exhaust gases of aircraft engines. In addition, non-target screening and in vitro bioassays on aviation-related PM2.5 filter samples were combined to provide indications for potential toxicologically relevant compounds in dependence of different wind directions and airport operations. Most recently, the applied non-target screening method was also used to identify seasonal variations in the organic aerosol composition in Beijing.
F-type ATP synthases are multiprotein complexes composed of two separate coupled motors (F1 and FO) generating adenosine triphosphate (ATP) as the universal major energy source in a variety of relevant biological processes in mitochondria, bacteria and chloroplasts. While the structure of many ATPases is solved today, the precise assembly pathway of F1FO-ATP synthases is still largely unclear. Here, we probe the assembly of the F1 complex from Acetobacterium woodii. Using laser induced liquid bead ion desorption (LILBID) mass spectrometry, we study the self-assembly of purified F1 subunits in different environments under non-denaturing conditions. We report assembly requirements and identify important assembly intermediates in vitro and in cellula. Our data provide evidence that nucleotide binding is crucial for in vitro F1 assembly, whereas ATP hydrolysis appears to be less critical. We correlate our results with activity measurements and propose a model for the assembly pathway of a functional F1 complex.
Die vorliegende Dissertation mit dem Titel “Structural dynamics of eukaryotic H/ACA RNPs from Saccharomyces cerevisiae & Structural dynamics of the Guanidine-II riboswitch from Escherichia coli” besteht aus zwei Projekten. Das erste Projekt befasst sich mit den eukaryotischen H/ACA Ribonukleoproteinen (RNP) aus der Hefe. Diese können sequenzspezifisch in der RNA ein Uridin Nukleotid in das Rotationsisomer Pseudouridin (Ψ) umwandeln. Die H/ACA RNPs bestehen aus einer Leit-RNA und vier Proteinen, der katalytisch aktiven Pseudouridylase Cbf5, Nhp2, Gar1 und Nop10. Die Leit-RNA besteht in Eukaryoten konserviert aus zwei Haarnadelstrukturen, die von einem H-Box oder ACA-Box Sequenzmotiv gefolgt sind. In jeder dieser Haarnadeln befindet sich ein ungepaarter Bereich, die sogenannte Pseudouridylierungstasche, wo durch komplementäre Basenpaarung die Ziel-RNA gebunden wird. Fehlerhafte H/ACA RNPs können beim Menschen zu schweren Krankheiten wie verschiedenen Krebsarten oder dem Knochenmarksversagen Dyskeratosis congenita führen, aber sie bieten auch Möglichkeiten zum Einsatz als Therapiemethode. In dieser Arbeit wurde hauptsächlich der zweiteilige Aufbau der H/ACA RNPs untersucht.
Dafür wurden zunächst die einzelnen Komponenten hergestellt werden. Cbf5, Nop10 und Gar1 wurden zusammen heterolog in E. coli exprimiert und gereinigt. Außerdem wurden mehrere Deletionsvarianten von Gar1 hergestellt. Zusätzlich wurde die Leit-RNA unmarkiert über T7 Transkription synthetisiert, sowie sechs verschiedene FRET-Konstrukte mit verschiedenen Markierungschemas der Fluorophore Cy3 und Cy5 über DNA-geschiente Ligation. Anschließend wurde über Größenausschlusschromatographie und radioaktiven Aktivitätsassays geprüft, dass sich die aktiven H/ACA RNPs in vitro aus den einzelnen Komponenten rekonstituieren lassen.
In smFRET Experimenten wurden einzelne Haarnadelstrukturen mit dem zweiteiligen Komplexen verglichen. Dabei konnte gezeigt werden, dass die H3 Haarnadel durch die Anwesenheit von H5 dynamischer und heterogener wurde, während H5 überwiegend unbeeinflusst war. Außerdem konnte die dreidimensionale Orientierung der Haarnadelstrukturen in verschiedenen Assemblierungsschritten mittels smFRET untersucht werden. Hier deutete sich an, dass in Abwesenheit von Proteinen beide Haarnadeln eher entgegengesetzt stehen als in einer parallelen Konformation. Cbf5 scheint den Linker zwischen den Beiden auszustrecken bzw. zu orientieren und die Haarnadelstrukturen etwas gegeneinander zu neigen. Ein Zusammenspiel von Nhp2 und Gar1 war nötig um die oberen Bereiche der Haarnadeln zusammenzuziehen. Es konnte auch ein Modell für den vollen H/ACA RNP vorgeschlagen werden. Im kompletten Komplex könnte das Zusammenziehen der Haarnadelstrukturen durch Nhp2 und Gar1 mit dem Effekt von Cbf5 konkurrieren und könnte hauptsächlich den oberen Bereich von H3 betreffen. Zum Schluss wurde das Zusammenspiel von Gar1 und Nhp2 auf eine Abhängigkeit von den RGG Domänen von Gar1 hin untersucht. Hier besteht möglicherweise eine Hierarchie, die eine Kooperativität von den N- und C-terminalen Domänen benötigt.
Das zweite Projekt befasst sich mit dem Guanidin-II Riboschalter aus E. coli. Der Riboschalter kann das toxische Molekül Guanidinium (Gdm+) spezifisch in seiner Aptamerdomäne binden und dadurch die Genexpression von Proteinen zur Detoxifizierung von Gdm+ aktivieren. Der Riboschalter besteht aus zwei Haarnadelstrukturen, mit einer Schleife, die aus der Sequenz ACGR besteht, wobei R ein Purin ist. In einem vorgeschlagenen Modell soll die Ribosomenbindestelle (Shine-Dalgarno Sequenz) in Abwesenheit von Ligand mit dem Linker komplementär Basenpaaren und so die Translation verhindern. Mit Ligand würde sich dann eine Schleifen-Schleifen Interaktion mit den beiden CG Basen ausbilden, wodurch die Anti-Shine-Dalgarno Sequenz nicht mehr zugänglich wäre. Bisherige Studien arbeiteten zumeist nur mit der Aptamerdomäne, den einzelnen Haarnadeln oder noch kleineren Elementen. In dieser Arbeit wurden die Strukturdynamiken von verschiedenen Längen, auch mit der Expressionsplatform, untersucht. Außerdem wurden verschiedene Mutationen analysiert und die Effekte auf den Riboschalter in seiner natürlichen Umgebung in E. coli.
Zunächst mussten insgesamt 24 FRET-Konstrukte hergestellt werden, die sich in Länge, Markierungsschema und Mutationen unterschieden. Hierfür wurde DNA-geschiente Ligation verwendet. Dank der verschiedenen Fluorophorpositionen konnte ein konformationelles Modell für die Aptamerdomäne vorgeschlagen werden. In diesem Modell könnte in Abwesenheit von Ionen das Aptamer offen vorliegen. Durch Mg2+ würde sich bereits eine lockere Schleifen-Schleifen Interaktion ausbilden. Zusätzlich deuten die Ergebnisse auf eine neue Konformation hin, der stabilisierten Schleifen-Schleifen Interaktion, bei der der Linker zusätzlich mit den Haarnadelstrukturen interagiert, beispielswese mit den Purinen an der vierten Schleifenposition...
Bleaching-independent, whole-cell, 3D and multi-color STED imaging with exchangeable fluorophores
(2018)
We demonstrate bleaching-independent STED microscopy using fluorogenic labels that reversibly bind to their target structure. A constant exchange of labels guarantees the removal of photobleached fluorophores and their replacement by intact fluorophores, thereby circumventing bleaching-related limitations of STED super-resolution imaging in fixed and living cells. Foremost, we achieve a constant labeling density and demonstrate a fluorescence signal for long and theoretically unlimited acquisition times. Using this concept, we demonstrate whole-cell, 3D, multi-color and live cell STED microscopy with up to 100 min acquisition time.
Alzheimer’s Disease (AD) is a progressive and irreversible neurodegenerative disorder, characterized by the accumulation of abeta-amyloid aggregates, which triggers tau hyperphosphorylation and neuronal loss. While the precise mechanisms underlying neurodegeneration in AD are not entirely understood, it is known that loss of proteostasis is implicated in this process. Maintaining neuronal proteostasis requires proper transfer RNA (tRNA) modifications, which are crucial for optimal translation. However, research into tRNA epitranscriptome in AD is limited, and it is not yet clear how alterations in tRNA modifying enzymes and tRNA modifications might contribute to disease progression. Here, we report that expression of the tRNA modifying enzyme ELP3 is reduced in the brain of AD patients and amyloid AD mouse models, suggesting ELP3 is implicated in proteostasis dysregulation observed in AD. To investigate the role of ELP3 specifically in neuronal proteostasis impairments in the context of amyloid pathology, we analyzed SH-SY5Y neuronal cells carrying the amyloidogenic Swedish familial AD mutation in the APP gene (SH-SWE) or the wild-type gene (SH-WT). Similarly to the amyloid mouse models, SH-SWE exhibited reduced levels of ELP3 which was associated with tRNA hypomodifications and reduced abundance, as well as proteostasis impairments. Furthermore, the knock-down of ELP3 in SH-WT recapitulated the proteostasis impairments observed in SH-SWE cells. Importantly, the correction of tRNA deficits due to ELP3 reduction rescued and reverted proteostasis impairments of SH-SWE and SH-WT knock-down for ELP3, respectively. Additionally, SH-WT exposed to the secretome of SH-SWE or synthetic amyloid aggregates recapitulate the SH-SWE phenotype, characterized by reduced ELP3 expression, tRNA hypomodification and increased protein aggregation. Taken together, our data suggest that amyloid pathology dysregulates neuronal proteostasis through the reduction of ELP3 and tRNA modifications. This study highlights the modulation of tRNA modifications as a potential therapeutic avenue to restore neuronal proteostasis in AD and preserve neuronal function.
Different modification pathways for m1A58 incorporation in yeast elongator and initiator tRNAs
(2022)
As essential components of the cellular protein synthesis machineries, tRNAs undergo a tightly controlled biogenesis process, which include the incorporation of a large number of posttranscriptional chemical modifications. Maturation defaults resulting in lack of modifications in the tRNA core may lead to the degradation of hypomodified tRNAs by the rapid tRNA decay (RTD) and nuclear surveillance pathways. Although modifications are typically introduced in tRNAs independently of each other, several modification circuits have been identified in which one or more modifications stimulate or repress the incorporation of others. We previously identified m1A58 as a late modification introduced after more initial modifications, such as Ѱ55 and T54 in yeast elongator tRNAPhe. However, previous reports suggested that m1A58 is introduced early along the tRNA modification process, with m1A58 being introduced on initial transcripts of initiator tRNAiMet, and hence preventing its degradation by the nuclear surveillance and RTD pathways. Here, aiming to reconcile this apparent inconsistency on the temporality of m1A58 incorporation, we examined the m1A58 modification pathways in yeast elongator and initiator tRNAs. For that, we first implemented a generic approach enabling the preparation of tRNAs containing specific modifications. We then used these specifically modified tRNAs to demonstrate that the incorporation of T54 in tRNAPhe is directly stimulated by Ѱ55, and that the incorporation of m1A58 is directly and individually stimulated by Ѱ55 and T54, thereby reporting on the molecular aspects controlling the Ѱ55 → T54 → m1A58 modification circuit in yeast elongator tRNAs. We also show that m1A58 is efficiently introduced on unmodified tRNAiMet, and does not depend on prior modifications. Finally, we show that the m1A58 single modification has tremendous effects on the structural properties of yeast tRNAiMet, with the tRNA elbow structure being properly assembled only when this modification is present. This rationalizes on structural grounds the degradation of hypomodified tRNAiMet lacking m1A58 by the nuclear surveillance and RTD pathways.