title: Cyc2p, a membrane-bound flavoprotein involved in the maturation of mitochondrial c-type cytochromes.
abstract: Mitochondrial apocytochrome c and c1 are converted to their holoforms in the intermembrane space by attachment of heme to the cysteines of the CXXCH motif through the activity of assembly factors cytochrome c heme lyase and cytochrome c1 heme lyase (CCHL and CC1HL). The maintenance of apocytochrome sulfhydryls and heme substrates in a reduced state is critical for the ligation of heme. Factors that control the redox chemistry of the heme attachment reaction to apocytochrome c are known in bacteria and plastids but not in mitochondria. We have explored the function of Cyc2p, a candidate redox cytochrome c assembly component in yeast mitochondria. We show that Cyc2p is required for the activity of CCHL toward apocytochrome c and c1 and becomes essential for the heme attachment to apocytochrome c1 carrying a CAPCH instead of CAACH heme binding site. A redox function for Cyc2p in the heme lyase reaction is suggested from 1) the presence of a noncovalently bound FAD molecule in the C-terminal domain of Cyc2p, 2) the localization of Cyc2p in the inner membrane with the FAD binding domain exposed to the intermembrane space, and 3) the ability of recombinant Cyc2p to carry the NADPH-dependent reduction of ferricyanide. We postulate that, in vivo, Cyc2p interacts with CCHL and is involved in the reduction of heme prior to its ligation to apocytochrome c by CCHL.
authors.affiliation: Department of Chemistry and Biochemistry, UCLA, Los Angeles, California 90095-1569, USA.
authors.forename: Delphine G
authors.initials: DG
authors.lastname: Bernard
authors.forename: Sophie
authors.initials: S
authors.lastname: Quevillon-Cheruel
authors.forename: Sabeeha
authors.initials: S
authors.lastname: Merchant
authors.forename: Bernard
authors.initials: B
authors.lastname: Guiard
authors.forename: Patrice P
authors.initials: PP
authors.lastname: Hamel
mesh_terms: D020816:Amino Acid Motifs; D001665:Binding Sites; D002352:Carrier Proteins / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism*; D045304:Cytochromes c / Q000378:metabolism*; D003575:Cytochromes c1 / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D005415:Flavins / Q000737:chemistry; D005420:Flavoproteins / Q000737:chemistry; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D006418:Heme / Q000737:chemistry; D007700:Kinetics; D008190:Lyases / Q000737:chemistry; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins; D008954:Models, Biological; D009154:Mutation; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000502:physiology*; D013367:Submitochondrial Particles / Q000378:metabolism; D013696:Temperature
chemical_list: C083336:CYC2 protein, S cerevisiae; D002352:Carrier Proteins; D005415:Flavins; D005420:Flavoproteins; D005656:Fungal Proteins; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; D006418:Heme; D045304:Cytochromes c; D003575:Cytochromes c1; D008190:Lyases; C031581:cytochrome C synthetase; C095893:CYT2 protein, S cerevisiae