title: Physical interaction of CcmC with heme and the heme chaperone CcmE during cytochrome c maturation.
abstract: Biogenesis of c-type cytochromes requires the covalent attachment of heme to the apoprotein. In Escherichia coli, this process involves eight membrane proteins encoded by the ccmABCDEFGH operon. CcmE binds heme covalently and transfers it to apocytochromes c in the presence of other Ccm proteins. CcmC is necessary and sufficient to incorporate heme into CcmE. Here, we report that the CcmC protein directly interacts with heme. We further show that CcmC co-immunoprecipitates with CcmE. CcmC contains two conserved histidines and a signature sequence, the so-called tryptophan-rich motif, which is the only element common to cytochrome c maturation proteins of bacteria, archae, plant mitochondria, and chloroplasts. We report that mutational changes of these motifs affecting the function of CcmC in cytochrome c maturation do not influence heme binding of CcmC. However, the mutants are defective in the CcmC-CcmE interaction, suggesting that these motifs are involved in the formation of a CcmC-CcmE complex. We propose that CcmC, CcmE, and heme interact directly with each other, establishing a periplasmic heme delivery pathway for cytochrome c maturation.
authors.affiliation: Institut für Mikrobiologie, Eidgenössische Technische Hochschule, Schmelzbergstrasse 7, CH 8092 Zürich, Switzerland.
authors.forename: Q
authors.initials: Q
authors.lastname: Ren
authors.forename: L
authors.initials: L
authors.lastname: Thony-Meyer
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017124:Conserved Sequence; D003574:Cytochrome c Group / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D006420:Hemeproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006639:Histidine; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009876:Operon; D010641:Phenotype; D010957:Plasmids; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D014364:Tryptophan
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; C492058:CcmC protein, E coli; C116246:CcmC protein, bacteria; C115384:CcmE protein, E coli; D003574:Cytochrome c Group; D029968:Escherichia coli Proteins; D006420:Hemeproteins; D008565:Membrane Proteins; D011994:Recombinant Proteins; D006639:Histidine; D014364:Tryptophan