title: Maturation of the unusual single-cysteine (XXXCH) mitochondrial c-type cytochromes found in trypanosomatids must occur through a novel biogenesis pathway.
abstract: The c-type cytochromes are characterized by the covalent attachment of haem to the polypeptide via thioether bonds formed from haem vinyl groups and, normally, the thiols of two cysteines in a CXXCH motif. Intriguingly, the mitochondrial cytochromes c and c1 from two euglenids and the Trypanosomatidae contain only a single cysteine within the haem-binding motif (XXXCH). There are three known distinct pathways by which c-type cytochromes are matured post-translationally in different organisms. The absence of genes encoding any of these c-type cytochrome biogenesis machineries is established here by analysis of six trypanosomatid genomes, and correlates with the presence of single-cysteine cytochromes c and c1. In contrast, we have identified a comprehensive catalogue of proteins required for a typical mitochondrial oxidative phosphorylation apparatus. Neither spontaneous nor catalysed maturation of the single-cysteine Trypanosoma brucei cytochrome c occurred in Escherichia coli. However, a CXXCH variant was matured by the E. coli cytochrome c maturation machinery, confirming the proposed requirement of the latter for two cysteines in the haem-binding motif and indicating that T. brucei cytochrome c can accommodate a second cysteine in a CXXCH motif. The single-cysteine haem attachment conserved in cytochromes c and c1 of the trypanosomatids is suggested to be related to their cytochrome c maturation machinery, and the environment in the mitochondrial intermembrane space. Our genomic and biochemical studies provide very persuasive evidence that the trypanosomatid mitochondrial cytochromes c are matured by a novel biogenesis system.
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK. allenj@bioch.ox.ac.uk
authors.forename: James W A
authors.initials: JW
authors.lastname: Allen
authors.forename: Michael L
authors.initials: ML
authors.lastname: Ginger
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Ferguson
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D000818:Animals; D003545:Cysteine / Q000235:genetics*; D003574:Cytochrome c Group / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics*; D019143:Evolution, Molecular; D014644:Genetic Variation / Q000235:genetics; D008928:Mitochondria / Q000201:enzymology*; D024101:Mitochondrial Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics; D014346:Trypanosoma brucei brucei / Q000201:enzymology*
chemical_list: D003574:Cytochrome c Group; D024101:Mitochondrial Proteins; D011994:Recombinant Proteins; D003545:Cysteine