title: A conserved haem redox and trafficking pathway for cofactor attachment.
abstract: A pathway for cytochrome c maturation (Ccm) in bacteria, archaea and eukaryotes (mitochondria) requires the genes encoding eight membrane proteins (CcmABCDEFGH). The CcmABCDE proteins are proposed to traffic haem to the cytochrome c synthetase (CcmF/H) for covalent attachment to cytochrome c by unknown mechanisms. For the first time, we purify pathway complexes with trapped haem to elucidate the molecular mechanisms of haem binding, trafficking and redox control. We discovered an early step in trafficking that involves oxidation of haem (to Fe(3+)), yet the final attachment requires reduced haem (Fe(2+)). Surprisingly, CcmF is a cytochrome b with a haem never before realized, and in vitro, CcmF functions as a quinol:haem oxidoreductase. Thus, this ancient pathway has conserved and orchestrated mechanisms for trafficking, storing and reducing haem, which assure its use for cytochrome c synthesis even in limiting haem (iron) environments and reducing haem in oxidizing environments.
authors.affiliation: Department of Biology, Washington University, St Louis, MO 63130, USA.
authors.forename: Cynthia L
authors.initials: CL
authors.lastname: Richard-Fogal
authors.forename: Elaine R
authors.initials: ER
authors.lastname: Frawley
authors.forename: Eric R
authors.initials: ER
authors.lastname: Bonner
authors.forename: Huifen
authors.initials: H
authors.lastname: Zhu
authors.forename: Brian
authors.initials: B
authors.lastname: San Francisco
authors.forename: Robert G
authors.initials: RG
authors.lastname: Kranz
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001665:Binding Sites; D045304:Cytochromes c / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D006418:Heme / Q000302:isolation & purification / Q000378:metabolism*; D006420:Hemeproteins / Q000302:isolation & purification / Q000378:metabolism*; D006873:Hydroquinones / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D008190:Lyases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D010084:Oxidation-Reduction; D011485:Protein Binding
chemical_list: D001425:Bacterial Outer Membrane Proteins; C451399:CcmH protein, E coli; D029968:Escherichia coli Proteins; D006420:Hemeproteins; D006873:Hydroquinones; D006418:Heme; D045304:Cytochromes c; D007501:Iron; D008190:Lyases; C031581:cytochrome C synthetase