title: Cytochrome c biogenesis in Campylobacter jejuni requires cytochrome c6 (CccA; Cj1153) to maintain apocytochrome cysteine thiols in a reduced state for haem attachment.
abstract: The microaerophilic food-borne pathogen Campylobacter jejuni uses complex cytochrome-rich respiratory chains for growth and host colonisation. Cytochrome c biogenesis requires haem ligation to reduced apocytochrome cysteines, catalysed by the cytochrome c synthase, CcsBA. While ccsBA could not be deleted, we showed that the thiol reductase DsbD and the CcsX homologue Cj1207 are involved in, but not essential for, cytochromes c biogenesis. Mutant phenotypic analyses and biochemical studies with purified proteins revealed that the mono-haem c-type cytochromes Cj1153 (CccA) and Cj1020 (CccB) and the di-haem Cj0037 (CccC) are electron donors to the cb-oxidase (CcoNOQP), with CccC being more efficient than CccA. Remarkably, cccA deletion or site-directed mutagenesis resulted in an almost complete loss of all other c-type cytochromes. Cytochrome c structural and biogenesis genes were still transcribed in the cccA deletion mutant and the quinol oxidase genes (cioAB) were up-regulated. Cytochrome c production could be rescued in this mutant by growth with exogenous dithiothreitol or L-cysteine, suggesting that in the absence of CccA, apocytochrome c haem binding motifs become oxidised, preventing haem attachment. Our results identify CccA, the most abundant periplasmic c-type cytochrome in C. jejuni, as a novel and unexpected protein required for cytochrome c biogenesis in this pathogen.
authors.affiliation: Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, UK.
authors.forename: Yang-Wei
authors.initials: YW
authors.lastname: Liu
authors.affiliation: Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Kelly
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D016123:Campylobacter jejuni / Q000235:genetics / Q000378:metabolism*; D003545:Cysteine / Q000378:metabolism; D045304:Cytochromes c / Q000096:biosynthesis* / Q000235:genetics; D045365:Cytochromes c6 / Q000378:metabolism*; D004579:Electron Transport; D004926:Escherichia coli / Q000235:genetics; D006418:Heme / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010088:Oxidoreductases / Q000378:metabolism; D013438:Sulfhydryl Compounds / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D045365:Cytochromes c6; D013438:Sulfhydryl Compounds; D006418:Heme; D045304:Cytochromes c; D010088:Oxidoreductases; C020094:duroquinol oxidase; D003545:Cysteine