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Bacterial Reaction Centers, 
Cytochrome bc-Complexes, Sulfide-Quinone Reductase

(According to the 8. Research Report of the University of Regensburg)

Research Projects:

Head: Prof. Dr. Günter Hauska
Coworkers: Monika Kammerer; in cooperation with Nathan Nelson (Tel Aviv, Israel), Prof. Dr. Georgios Tsiotis (Iraklion, Greece/ 2D-crystallization). 
1. The P840-Reaction Center from Green Sulfur Bacteria

Description: The photosynthetic reaction centers (RCs) occur in two types, either with FeS-centers (type 1 = FeS-type), or with quinones (type 2 = Q-type) as the terminal electron acceptors. High resolution X-ray crystallogaphy of the RCs from purple bacteria (Q-type) and from cyanobacterial PS1 (FeS-type) revealed that both are organized in a heterodimeric, transmembrane arrangement. Two different core polypeptides hold a pseudosymmetric double set of the redox components, only one of them being used in efficient electron transfer. Why? This still open question may be answered by studying the P840-RC from green sulfur bacteria, which, together with the one from heliobacteria, seems to represent a homodimeric FeS-type RC, with two identical core polypeptides. Single particle analysis by scanning transmission electron microscopy is in line with this notion, and we concentrate our efforts to obtain 2d- and/or 3d-crystals for final proof. Also electron transfer may be simpler in the P840-RC than in PS1. By EPR and other techniques we pursue the indication that a quinone, like phylloquinone in PS1 as the early electron acceptor A1, is not obligatorily required in green sulfur bacteria. 
Grants: DFG (Ha 852/12), ESF 


Head: Prof. Dr. Günter Hauska, Dr. Iris Maldener 
Coworkers: Monika Kammerer
2. Function and Organization of the Cytochrome b6f Complex in the Heterocyst Forming Cyanobacterium Anabaena variabilis

Description: Cytochrome bc-complexes function as quinol oxidizing, proton translocating oxidoreductases in many electron transport chains, from Eubacteria and Archaea up to mitochondria and chloroplasts of Eukarya. Among them, in organisms performing oxygenic photosynthesis, the cytochrome b6f complex transfers electrons from PSII to PSI, and is also required for cyclic electron flow around PSI. It contains four essential proteins (Cytochrome f/PetA, Cytochrome b6/PetB, the Rieske Fe-S protein/PetC and subunit IV/PetD), which in Cyanobacteria are encoded by the petCA and petBD operons, respectively. Additionally to these proteins there are three to four hydrophopbic, very small polypeptides (PetG, PetL, PetM and PetN) which are supposed to function in assembly, stability and/or modulation of the catalytic activity. In Cyanobacteria the b6f complex also functions in dark respiration, taking over a pivotal role in metabolism. Several filamentous cyanobacterial strains, like Anabaena variabilis, are able to fix atmospheric N2 under microaerobic conditions by protecting nitrogenase from oxygen in specialized cells. These heterocysts develop from vegetative cells in a regular pattern along the filament. Heterocysts possess a thick envelope (reduced entrance of O2), PSII is inactive (no O2 evolution) and respiration is accelerated (consumption of O2). For production of ATP cyclic electron flow around PSI remains next to respiration, and thus the b6f complex is present. During the differentiation process dramatical changes in expression of a number of proteins occur. Transiently increased transcription of the petCA and petBD operons has been observed. Whether a heterocyst-specific regulation of the b6f complex takes place is still unknown, however. In this respect we are interested in the role of the small subunits and the function of an additional Rieske Fe-S protein, which was recently found in Anabaena.
Grants: DFG (Ma 1359/3) 


Head: Prof. Dr. Günter Hauska
Coworkers:  Thomas Schödl, PD Dr. Iris Maldener, in cooperation with PD Dr. Rita Grandori (University of Linz, Austria), Dr. Yosepha Shahak (Volcani Center, Bet Dagan, Israel) 
3. Sulfide-Quinone-Reductase

Description: Some cyanobacteria are able to switch from oxygenic photosynthesis to sulfide oxidation under extreme conditions. Anoxygenic photosynthesis then is similar to photosynthesis of green sulfur bacteria and purple bacteria. We found that sulfide oxidation in cyanobacteria and other bacteria involves quinone and cytochrome bc1 complex. Sulfide quinone reductase was purified from the cyanobacterium Oscillatoria limnetica and from the purple bacterium Rhodobacter capsulatus and characterized as a novel flavoprotein. The gene encoding the SQR from Rhodobacter capsulatus has been cloned, sequenced and functionally expressed in E. coli. It has been shown that SQR is essential for photoautotrophic growth on sulfide. SQR activity has been detected in membranes of a number of further bacteria. At present we study regulation of SQR expression and the catalytic mechanism. In collaboration with Prof. O. Wolfbeis  we try to adapt SQR for microanalysis of sulfide via its flavine fluorescence. 

Literatur:
Griesbeck C., Hauska G. and Schütz M. (2000) Biological Sulfide Oxidation: Sulfide-Quinone Reductase (SQR), the Primary Reaction, Recent Research Developments in Microbiology 4, 179-203 (Download PDF-file)

Grants: DFG (Ha 852/10-3)