A New Membrane-bound Cytochrome c Works as an Electron Donor to the Photosynthetic Reaction Center Complex in the Purple Bacterium, Rhodovulum sulfidophilum

• Published in: The Journal of biological chemistry Vol. 282; no. 9; pp. 6463 - 6472
• Main Authors: Kimura, Yasuaki, Alric, Jean, Verméglio, André, Masuda, Shinji, Hagiwara, Yuuki, Matsuura, Katsumi, Shimada, Keizo, Nagashima, Kenji V.P.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 02-03-2007; American Society for Biochemistry and Molecular Biology
• Subjects: Anaerobiosis; Bacterial Proteins - physiology; Cytochromes c - physiology; Electron Transport - physiology; Kinetics; Membrane Proteins; Molecular Sequence Data; Molecular Weight; Mutation; Oxidation-Reduction; Photosynthetic Reaction Center Complex Proteins; Phylogeny; Rhodovulum - chemistry; Rhodovulum sulfidophilum
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M604452200

A new type of membrane-bound cytochrome c was found in a marine purple photosynthetic bacterium, Rhodovulum sulfidophilum. This cytochrome c was significantly accumulated in cells growing under anaerobic photosynthetic conditions and showed an apparent molecular mass of ∼100 kDa when purified and analyzed by SDS-PAGE. The midpoint potential of this cytochrome c was 369 mV. Flash-induced kinetic measurements showed that this new cytochrome c can work as an electron donor to the photosynthetic reaction center. The gene coding for this cytochrome c was cloned and analyzed. The deduced molecular mass was nearly equal to 50 kDa. Its C-terminal heme-containing region showed the highest sequence identity to the water-soluble cytochrome c2, although its predicted secondary structure resembles that of cytochrome cy. Phylogenetic analyses suggested that this new cytochrome c has evolved from cytochrome c2. We, thus, propose its designation as cytochrome c2m. Mutants lacking this cytochrome or cytochrome c2 showed the same growth rate as the wild type. However, a double mutant lacking both cytochrome c2 and c2m showed no growth under photosynthetic conditions. It was concluded that either the membrane-bound cytochrome c2m or the water-soluble cytochrome c2 work as a physiological electron carrier in the photosynthetic electron transfer pathway of Rvu. sulfidophilum.