SPP 1070, Subproject: Structure and function of the soxLN complex of Sulfolobus, the first archaeal analog of the cytochrome bc1/b6f complex

Cytochrome bc1- and the closely related b6f-complexes are almost ubiquitously distributed among the bacteria and eukarya. They consist of a minimum of three subunits: A membrane bound c- or f-type cytochrome, a membrane bound di-heme b-type cytochrome and a Rieske iron sulfur protein. They catalyse the oxidation of ubi-, plasto-, or menaquinol with a soluble c-type cytochrome or a blue copper protein acting as electron acceptor. The free energy of this reaction is used to translocate one additional proton per electron across the membrane. The bacterial and eukaryal complexes have been studied in great detail. Recently the x-ray structures of the isolated Rieske proteins from beef heart mitochondria and spinach chloroplasts as well as of the entire beef heart bc1-complex have been solved. Almost nothing is known about the archeal equivalents of these complexes. We identified two membrane bound Rieske proteins in the hyper thermoacidophilic crenarchaeon Sulfolobus acidocaldarius, but very little is known about their structure and functional context. Since the presence of membrane bound Rieske proteins is - at least in bacteria and eukarya - indicative for the presence of a cytochrome bc1- or b6f-complex and one of the isolated Sulfolobus Rieske proteins displays the same ubiquinol: cytochrome c reductase activity as it was described for the protein from beef heart mitochondria, Sulfolobus is a prime candidate to search for and to investigate the structure and the function of an archeal equivalent to the bc1-/ b6f-complexes.