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Background: In many species males face a higher predation risk than females because males display elaborate traits that evolved under sexual selection, which may attract not only females but also predators. Females are, therefore, predicted to avoid such conspicuous males under predation risk. The present study was designed to investigate predator-induced changes of female mating preferences in Atlantic mollies (Poecilia mexicana). Males of this species show a pronounced polymorphism in body size and coloration, and females prefer large, colorful males in the absence of predators. Results: In dichotomous choice tests predator-naïve (lab-reared) females altered their initial preference for larger males in the presence of the cichlid Cichlasoma salvini, a natural predator of P. mexicana, and preferred small males instead. This effect was considerably weaker when females were confronted visually with the non-piscivorous cichlid Vieja bifasciata or the introduced non-piscivorous Nile tilapia (Oreochromis niloticus). In contrast, predator experienced (wild-caught) females did not respond to the same extent to the presence of a predator, most likely due to a learned ability to evaluate their predators' motivation to prey. Conclusions: Our study highlights that (a) predatory fish can have a profound influence on the expression of mating preferences of their prey (thus potentially affecting the strength of sexual selection), and females may alter their mate choice behavior strategically to reduce their own exposure to predators. (b) Prey species can evolve visual predator recognition mechanisms and alter their mate choice only when a natural predator is present. (c) Finally, experiential effects can play an important role, and prey species may learn to evaluate the motivational state of their predators. Keywords: Sexual selection; female choice; non-independent mate choice; predator recognition; Poecilia mexicana
As a part of this thesis, a Monte Carlo-based code has been developed capable of simulating the transition of proton beam properties to neutron beam properties as it occurs in the Li-7(p, n)Be-7 reaction. It is able to reproduce not only the angle-integrated energy distributions but it is also capable of predicting the angle-dependent neutron spectra as measured at Forschungszentrum Karlsruhe (Karlsruhe, Germany) and Physikalisch-Technische Bundesanstalt (Braunschweig, Germany). Since the code retains all three spatial dimensions as well as all three velocity dimensions, it provides very detailed information on the neutron beam. The resulting data can aid in many different aspects, for example it can be used in shielding construction, or for lithium target design. In this work, the code is used to predict the neutron beam properties expected at the Frankfurt Neutron Source at Stern-Gerlach-Zentrum (FRANZ) facility. For different proton beam energies, the neutron distribution in x/p_x, y/p_y, and z/p_z is shown as well as a Mollweide projection, which illustrates the kinematic collimation effect that limits the neutron cone opening angle to less than 180 degree.
Die Familie der Proteorhodopsine (PR) besteht aus Hunderten von PR Molekülen, die unter Lichteinwirkung Protonen pumpen und somit eine bedeutende Rolle für die Energiegewinnung spielen könnten. Da der pKa Wert des Proton Akzeptors der Schiff‘schen Base (SB) (~7.2) dem pH Wertes der Ozeane (~7.9) ähnelt, wird auch über eine regulatorische Funktion spekuliert. Wird in Erwägung gezogen, dass 24 000 PR Moleküle pro SAR86 Zelle vorhanden sind (Beja et al. 2001) und dass 13% der Bakterien der Meeresoberfläche PR besitzen (Sabehi et al. 2005) liefert dieses Protein wahrscheinlich einen bedeutenden Energiebeitrag neben der Photosynthese. Einblicke in den Mechanismus der Energieumwandlung erfordern sowohl die Untersuchung des Chromophores, welches die Lichtenergie absorbiert als auch der Struktur des Apoproteins, das durch die Generierung eines Protonengradienten zur Energiegewinnung beiträgt. Der Fokus der Doktorarbeit liegt auf dem Chromophor und seiner Umgebung. Eine erste Charakterisierung der SB und des Retinals erfolgt durch UV/VIS und NMR Messungen (Pfleger et al. 2008). Die 13C chemische Verschiebungen von 10,11-13C2 Retinal und die 15N chemische Verschiebung der protonierten SB, gebildet durch K231, zeigt eindeutig, dass im Grundzustand nur eine Konformation der Retinals, all-trans, vorliegt. Die 15N chemische Verschiebung weist außerdem auf eine starke Wechselwirkung der SB mit ihren Gegenionen hin. Desweiteren kann durch Messungen der 15N chemischen Verschiebung der SB bei verschiedenen pH Werten der pKa Wert der SB abgeschätzt werden, auf ~12. Diese Stabilisierung der positiv geladenen protonierten Form der SB weist auf die Existenz eines Wasserclusters hin, das durch die hohe Dielektrizitätskonstante die protonierte Form der SB stabilisieren könnte. Um zu überprüfen, ob Wasser an der SB gebunden ist, wird ein sogenanntes 15N-1H HETCOR Experiment durchgeführt. Der Bereich der 15N chemischen Verschiebung der SB korreliert mit einer Protonenresonanz bei ~5 ppm, welche im Bereich einer Wasserresonanz liegt und die durch D2O austauschbar ist. Dies indiziert eine wichtige Bedeutung von Wasser in der Nähe der SB für die Funktion von PR. Der Einfluss von Mutationen des Histidins H75 und des Aspartats D97 auf die 15N chemische Verschiebung der SB sowie die Auswirkung von Histidinmutationen auf das Chromophor deuten eine direkte Wechselwirkung von Aspartat 97 und der SB an, nicht aber eine direkte Wechselwirkung von H75 und der SB. Neben dem Chromophor ist außerdem das Signalpeptid Gegenstand der Untersuchung der Doktorarbeit. Motivation für die Untersuchung war die Inhomogenität der Proben, die im Zusammenhang mit ungleich prozessiertem PR stehen könnten. Ein zweiter Teil beschäftigt sich mit neuen Konzepten der Datenaufnahme, da das S/R in der Festkörper NMR ein limitierender Faktor darstellt. Diese beinhalten Verstärkung der Relaxation (RELOAD) sowie die Refokussierung von T2 bei Verwendung eines Prozessierungsschrittes, der „half echo alternating transformation“ (HEAT).
In mitochondrial respiration, the soluble protein cytochrome c accepts an electron from the membrane bound cytochrome bc1. The interaction between cytochrome bc1 and cytochrome c is highly transient in nature, enabling turnover numbers greater than 160 s-1. Yeast cytochrome bc1 has been successfully crystallised with bound cytochrome c with the help of an antibody fragment (Lange and Hunte 2002; Solmaz and Hunte 2008). In all crystal structures of the complex, the homodimeric cytochrome bc1 binds only one cytochrome c, with the binding site located on subunit cytochrome c1. Univalent cytochrome c binding is correlated with conformational changes of the Rieske protein head domain and subunit QCR6p. The interface of the complex is small. The haem moieties are centrally located in a mainly non-polar contact site that includes a cation–! interaction and is surrounded by complementary charged residues. The crystal structure is in agreement with the general architecture of the interfaces of transient redox complexes and also reveals several interesting features unique to the cytochrome bc1. On the basis of the crystal structures, an extensive thermodynamic and kinetic characterisation of the interaction was carried out in this work to challenge the static snapshot of the bound proteins in the crystal structure as the relevant physiological electron transfer. The thermodynamic parameters of the interaction between the redox partners were determined using isothermal titration calorimetry (ITC). The association constant for cytochrome bc1 and cytochrome c in oxidised state under physiological ionic strength of 120 mM at 25 °C, was determined to be 5 " 103 M-1 by direct ITC titration. So, the partners interact with an affinity of 200 #M. In spite of the low affinity the complex has a life time ($ = 1/koff) of 5 #second, sufficiently long to enable the theoretically calculated electron transfer rates of 1.0 " 106 to 2.6 " 107 s%1 with a lifetime ($ = 1/rate) of 1-0.04 μseconds and experimentally determined rate of 7.7 " 104 s%1 with a lifetime of 13 μseconds. The low affinity makes it difficult to ascertain the stoichiometry of binding. The enthalpy of the interaction is endothermic, which is consistent with the nature of an interface where hydrophobic interactions are dominant. The enthalpy and entropy is 3.6 kJmol-1 and 83 kJmol-1K-1, respectively. The importance of key interface residues was also investigated. The role of the interface residue G89 of cytochrome c which might have a role in the dissociation of the complex has been probed by site-directed mutagenesis. The interface contains a cation-! interaction between F230 of cytochrome bc1 and R19 of cytochrome c, which is thought to provide the specificity to the interaction between the otherwise promiscuous partners. To analyse the role of this interaction pair in electron transfer, F230L and F230W mutants were used to measure direct electron transfer rates by flash photolysis and steady state kinetics. The findings indicate that another ! system can work as functional substitution of F230, while deleting the ! system has a deleterious effect on the complex formation. The inability of F230L to achieve the transient and steady state turnover rates as wild type protein indicates a scenario where the variant achieves an altered bound state with inefficient electron transfer pathways and higher edge-to-edge distance. The role of supernumerary subunit QCR6p in complex formation was investigated by steady state kinetics measurements. Subunit QCR6p does not interact directly with cytochrome c but is positioned in such a way that it could electrostatically steer cytochrome c in a reactive ensemble. The highly acidic and disordered N-terminus of QCR6p could interact with a patch of conserved lysine residues on cytochrome c. The role of subunit QCR6p has been assessed using QCR6p deleted cytochrome bc1 and a lysine variant of cytochrome c. The results show that QCR6p not only affects the kinetics of the interaction but is also important for the stability of cytochrome bc1. The kinetic and thermodynamic data obtained during this study provide evidence for the functional importance of non-catalytic cytochrome bc1 subunit QCR6p, show that the entropy driven interaction is indeed of low affinity and highly transient in nature and indicate that the interface is well suited to ensure the high turnover of the electron transfer chain where cytochrome c interacts with multiple partners using overlapping interfaces. The suggested role of the cation-! interaction as a highly specific interaction has been validated.
This thesis is based on the following publications (in chronological order): 1. Biegel, E., S. Schmidt & V. Müller (2009) Genetic, immunological and biochemical evidence for a Rnf complex in the acetogen Acetobacterium woodii. Environ. Microbiol. 11: 1438-1443. My contribution: Amplification, sequence determination and analysis of Rnf homologues, enrichment of the Rnf complex 2. Biegel, E. & V. Müller (2010) Bacterial Na+-translocating ferredoxin:NAD+ oxidoreductase. Proc. Nat. Acad. Sci. U. S. A. 107: 18138-18142. My contribution: I designed and performed all experiments shown and interpreted the data. 3. Biegel, E., S. Schmidt, J. Gonzáles & V. Müller (2010) Biochemistry, evolution and physiological function of the Rnf complex, a novel ion-motive electron transport complex in prokaryotes. Cell. Mol. Life Sci., in press. DOI: 10.1007/s00018-010-0555-8. My contribution: I was involved in writing all chapters except chapters: „phylogenetic analyses of rnf genes“ and „distribution of rnf genes“. 4. Biegel, E. & V. Müller (2010) A Na+-translocating pyrophosphatase in the acetogenic bacterium Acetobacterium woodii. J. Biol. Chem., in press. DOI: 10.1074/jbc.M110.192823. My contribution: I designed and performed all experiments shown and interpreted the data.
The molecular conformation of the title compound, C18H18N2O3S, is stabilized by an intramolecular N—H ... O hydrogen bond. The crystal packing shows centrosymmetric dimers connected by N—H ... S hydrogen bonds. The terminal ethoxy substituents are statistically disordered [occupancy ratio 0.527 (5):0.473 (5)].
The title compound, C20H22O4S2, was synthesized by the reaction of 1,4-dibromobutene with methyl thiosalicylate. The aliphatic segment of this ligand is in an all-trans conformation. The bridging chain, –S-(CH2)4-S–, is almost planar (r.m.s. deviation for all non-H atoms: 0.056 Å) and its mean plane forms dihedral angles of 16.60 (7) and 5.80 (2)° with the aromatic rings. In the crystal, the molecules are linked by weak C—H ... O interactions into chains with graph-set notation C(14) along [0 0 1]. The crystal studied was a racemic twin, the ratio of the twin components being 0.27 (9):0.73 (9).
The title compound, C14H11NO4, crystallizes with two molecules in the asymmetric unit. The major conformational difference between these two molecules is the dihedral angle between the aromatic rings, namely 36.99 (5) and 55.04 (5)°. The nitro groups are coplanar with the phenyl rings to which they are attached, the O—N—C—C torsion angles being -1.9 (3) and 1.0 (3)° in the two molecules.
The 3,5-methoxy groups in the title compound, C16H23NO4, are almost coplanar with the aromatic ring, whereas the 4-methoxy group is bent out of this plane. The three CH3—O—C—C torsion angles are -1.51 (18), 0.73 (19) and 75.33 (15)°. The cyclohexane ring adopts a chair conformation. In the crystal, molecules are connected by intermolecular N—H ... O hydrogen bonds into chains running along the b axis.
The title compound. C15H14N2O4, (I), has a gauche–gauche (O/C/C/C—O/C/C/C or GG) conformation and is a positional isomer of propane-1,3-diyl bis(pyridine-3-carboxylate), (II). The molecule of (I) lies on a twofold rotation axis, which passes through the central C atom of the aliphatic chain, giving one half-molecule per asymmetric unit. There is excellent agreement of the geometric parameters of (I) and (II). The most obvious differences between them are the O/C/C/C—O/C/C/C torsion angles [56.6 (2)° in (I) and 174.0 (3)/70.2 (3)° in (II) for GG and TG conformations, respectively] and the dihedral angle between the planes of the aromatic rings [80.3 (10)° in (I) and 76.5 (3)° in (II)]. The crystal structure is stabilized by weak C—H ... N and C—H ... O hydrogen bonding.
4-Nitrophenyl 1-naphthoate
(2010)
In the title compound, C17H11NO4, the dihedral angle between the two benzene rings is 8.66 (3)°. The nitro group is twisted by 4.51 (9)° out of the plane of the aromatic ring to which it is attached. The presence of intermolecular C—H ... O contacts in the crystal structure leads to the formation of chains along the c axis.
The title compound, C6H5NO2·C6H6O2, crystallizes with one pyridinium-2-carboxylate zwitterion and one molecule of benzene-1,2-diol in the asymmetric unit. The crystal structure is characterized by alternating molecules forming zigzag chains running along the a axis: the molecules are connected by O—H ... O and N—H ... (O,O) hydrogen bonds.
Crystals of the title compound, C12H8N2·C7H8O2, were obtained during cocrystallization experiments of a compound with two hydrogen-bond donors (2-hydroxybenzyl alcohol) with another compound containing two hydrogen-bond acceptors (phenanthroline). Unexpectedly, the two molecules do not form dimers with two O—H ... N hydrogen bonds connecting the two molecules. However, one of the hydroxy groups forms a bifurcated hydrogen bond to both phenanthroline N atoms, whereas the other hydroxy group forms an O—H ... O hydrogen bond to a symmetry-equivalent 2-hydroxybenzyl alcohol molecule. In addition, the crystal packing is stabilized by Pi – Pi interactions between the two phenanthroline ring systems, with a centroid–centroid distance of 3.570 Å.
In the crystal of the title compound [systematic name: 2-(3,5-diamino-6-chloropyrazin-2-ylcarbonyl)guanidinium chloride methanol disolvate], C6H9ClN7O+·Cl-·2CH3OH , the components are connected by N—H ... N, N—H ... Cl, N—H ... O, O—H ... Cl and O—H ... O hydrogen bonds into a three-dimensional network. The dihedral angle between the aromatic ring and the guanidine residue is 6.0 (2)°.
In contrast to the previous structure determinations of the title structure, (NH4)2[MoS4], the present determination at 173 K localized the positions of the H atoms. The title structure belongs to the beta-K2SO4 family and all the ions are located on crystallographic mirror planes. The ions are held together by N—H ... S hydrogen bonds (some of which are bifurcated), forming a three-dimensional network. One of the N atoms has nine contacts to the S atoms shorter than 4 Å, and the other has ten.
The title compound (also know as azorellanone), C20H32O2, is built up from three fused carbocycles, one five-membered ring and two six-membered rings. The five membered-ring has an envelope conformation, whereas the six-membered rings have a distorted half-chair and a twist–boat conformation. In the crystal, molecules are linked by O—H ... O interactions into zigzag chains with graph-set notation C(8) along [010]. The absolute configuration was assigned on the basis of earlier chemical studies.
The dihydropyrimidine ring of the title compound, C13H15ClN2S, adopts an envelope conformation with five almost coplanar atoms (r.m.s. deviation = 0.054 Å) and the C atom bearing the two methyl substituents deviating from this plane by 0.441 (2) Å. The best plane through the five almost coplanar atoms forms a dihedral angle of 89.56 (5)° with the benzene ring. The crystal packing is characterized by centrosymmetric dimers connected by pairs of N—H ... S hydrogen bonds.
9-Bromo-9-borafluorene
(2010)
The title compound, C12H8BBr, crystallizes with three essentially planar molecules (r.m.s. deviations = 0.018, 0.020 and 0.021Å) in the asymmetric unit: since the title compound is rigid, there are no conformational differences between these three molecules. The crystal packing resembles a herringbone pattern.