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Chromalveolates are a diverse group of protists that include many ecologically and medically relevant organisms such as diatoms and apicomplexan parasites. They possess plastids generally surrounded by four membranes, which evolved by engulfment of a red alga. Today, most plastid proteins must be imported, but many aspects of protein import into complex plastids are still cryptic. In particular, how proteins cross the third outermost membrane has remained unexplained. We identified a protein in the third outermost membrane of the diatom Phaeodactylum tricornutum with properties comparable to those of the Omp85 family. We demonstrate that the targeting route of P. tricornutum Omp85 parallels that of the translocation channel of the outer envelope membrane of chloroplasts, Toc75. In addition, the electrophysiological properties are similar to those of the Omp85 proteins involved in protein translocation. This supports the hypothesis that P. tricornutum Omp85 is involved in precursor protein translocation, which would close a gap in the fundamental understanding of the evolutionary origin and function of protein import in secondary plastids.
The social amoeba Dictyostelium discoideum is a widely used model organism for studying basic functions of protozoan and metazoan cells, such as osmoregulation and cell motility. There is evidence from other species that cellular water channels, aquaporins (AQP), are central to both processes. Yet, data on D. discoideum AQPs is almost absent. Despite cloning of two putative D. discoideum AQPs, WacA, and AqpA, water permeability has not been shown. Further, WacA and AqpA are expressed at the late multicellular stage and in spores but not in amoebae. We cloned a novel AQP, AqpB, from amoeboidal D. discoideum cells. Wild-type AqpB was impermeable to water, glycerol, and urea when expressed in Xenopus laevis oocytes. Neither stepwise truncation of the N terminus nor selected point mutations activated the water channel. However, mutational truncation by 12 amino acids of an extraordinary long intracellular loop induced water permeability of AqpB, hinting at a novel gating mechanism. This AqpB mutant was inhibited by mercuric chloride, confirming the presence of a cysteine residue in the selectivity filter as predicted by our structure model. We detected AqpB by Western blot analysis in a glycosylated and a non-glycosylated form throughout all developmental stages. When expressed in D. discoideum amoebae, AqpB-GFP fusion constructs localized to vacuolar structures, to the plasma membrane, and to lamellipodia-like membrane protrusions. We conclude that the localization pattern in conjunction with channel gating may be indicative of AqpB functions in osmoregulation as well as cell motility of D. discoideum.
The role of TolC has largely been explored in proteobacteria, where it functions as a metabolite and protein exporter. In contrast, little research has been carried out on the function of cyanobacterial homologues, and as a consequence, not much is known about the mechanism of cyanobacterial antibiotic uptake and metabolite secretion in general. It has been suggested that the TolC-like homologue of the filamentous, heterocyst-forming cyanobacterium Anabaena sp. PCC 7120, termed heterocyst glycolipid deposition protein D (HgdD), is involved in both protein and lipid secretion. To describe its function in secondary metabolite secretion, we established a system to measure the uptake of antibiotics based on the fluorescent molecule ethidium bromide. We analyzed the rate of porin-dependent metabolite uptake and confirmed the functional relation between detoxification and the action of HgdD. Moreover, we identified two major facilitator superfamily proteins that are involved in this process. It appears that anaOmp85 (Alr2269) is not required for insertion or assembly of HgdD, because an alr2269 mutant does not exhibit a phenotype similar to the hgdD mutant. Thus, we could assign components of the metabolite efflux system and describe parameters of detoxification by Anabaena sp. PCC 7120.
Statistical physics of power flows on networks with a high share of fluctuating renewable generation
(2010)
Renewable energy sources will play an important role in future generation of electrical energy. This is due to the fact that fossil fuel reserves are limited and because of the waste caused by conventional electricity generation. The most important sources of renewable energy, wind and solar irradiation, exhibit strong temporal fluctuations. This poses new problems for the security of supply. Further, the power flows become a stochastic character so that new methods are required to predict flows within an electrical grid. The main focus of this work is the description of power flows in a electrical transmission network with a high share of renewable generation of electrical energy. To define an appropriate model, it is important to understand the general set-up of a stable system with fluctuating generation. Therefore, generation time series of solar and wind power are compared to load time series for whole Europe and the required balancing or storage capacities analyzed. With these insights, a simple model is proposed to study the power flows. An approximation to the full power flow equations is used and evaluated with Monte-Carlo simulations. Further, approximations to the distributions of power flows along the links are analytically derived. Finally, the results are compared to the power flows calculated from the generation and load data.
Event-by-event multiplicity fluctuations in nucleus-nucleus collisions are studied within the HSD and UrQMD transport models. The scaled variances of negative, positive, and all charged hadrons in Pb+Pb at 158 AGeV are analyzed in comparison to the data from the NA49 Collaboration. We find a dominant role of the fluctuations in the nucleon participant number for the final hadron multiplicity fluctuations. This fact can be used to check di erent scenarios of nucleus-nucleus collisions by measuring the final multiplicity fluctuations as a function of collision centrality. The analysis reveals surprising e ects in the recent NA49 data which indicate a rather strong mixing of the projectile and target hadron production sources even in peripheral collisions. PACS numbers: 25.75.-q,25.75.Gz,24.60.-k
TABLE OF CONTENTS (here without authors) Introduction 1. Em Busca dos Sítios do Poder na África Centro Ocidental. Homens e Caminhos, Exércitos e Estradas (1483-1915) 2. The Supply and Deployment of Horses in Angolan Warfare (17th and 18th Centuries) 3. Wagon Technology, Transport and Long-distance Communication in Angola 1885-1908 4. Trade, Slavery, and Migration in the Interior of Benguela: The Case of Caconda, 1830-1870 5. The Economics of the Kwango Rubber Trade, c. 1900 6. As Vias de Comunicação e Meios de Transporte como Factores de Globalização, de Estabilidade Política e de Transformação Económica e Social: Caso do Caminho-de-ferro de Bengela (Benguela) (1889-1950) 7. Nas Malhas da Rede: Aspectos do impacto económicoe social do transporte rodoviário na região do Huambo c. 1920-c. 1960 8. Communications between Angola and East Central Africa Before c. 1700 9. Long-distance Caravans and Communication beyond the Kwango (c. 1850-1890) 10. A Escrita em Angola: Comunicação e Ruído entre as Diferentes Sociedades em Presença 11. Escrever o Poder: Os Autos de Vassalagem e a Vulgarização da Escrita entre as Elites Africanas Ndembu 12. Do Passado ao Presente: Tráfego Comercial e Redes de Comunicação, Factores Privilegiados de “Modernidade” 13. Refugees on Routes. Congo / Zaire and the War in Northern Angola (1961-1974) 14. Crossing the River: Myth and Movement in Central Africa 15. From Group Mobility to Individual Movement: The Colonial Effort to Turn Back History Notes on Contributors