Genes for cytochrome c and cytochrome c oxidase synthesis in Bacillus subtilis

Cytochromes are heme-containing proteins that function in electron transfer reactions, e.g. respiration and photosynthesis. There are several different types of cytochromes. C-type cytochromes differ from other types of cytochromes in that the heme group is covalently attached to the polypeptide via thioether bonds to two cysteinyl residues in a consensus motif, Cys-Xaa-Yaa-Cys-His. Cytochrome c oxidase is an energy transducing membrane-bound enzyme with two heme groups and two copper centres. This enzyme reduces molecular oxygen to water and is essential for animals, plants and many micro-organisms. This thesis addresses questions about how cytochrome c and cytochrome c oxidases are synthesised in living cells. From these studies one also obtains general knowledge about the biosynthesis of other types of metal-containing proteins. The Gram-positive soil bacterium Bacillus subtilis was previously known to contain three c-type cytochromes: QcrC, the cytochrome c of the bc complex; CtaC, the subunit II of cytochrome c oxidase; and CccA, the cytochrome c550. In the thesis it is demonstrated that the cccB gene encodes a fourth cytochrome c, cytochrome c551. Furthermore it is shown that CtaC is a lipoprotein and that the processing of the polypeptide is important for the function of cytochrome c oxidase. By screening different libraries of mutants for deficiency in functional cytochrome c oxidase and lack of all cytochrome c the proteins encoded by the resB and resC genes were found to be important for cytochrome c synthesis in B. subtilis. Two genes, ctaG and ypmQ, were found to encode proteins important for synthesis of functional cytochrome c oxidase.