title: ABC transporter-mediated release of a haem chaperone allows cytochrome c biogenesis.
abstract: Although organisms from all kingdoms have either the system I or II cytochrome c biogenesis pathway, it has remained a mystery as to why these two distinct pathways have developed. We have previously shown evidence that the system I pathway has a higher affinity for haem than system II for cytochrome c biogenesis. Here, we show the mechanism by which the system I pathway can utilize haem at low levels. The mechanism involves an ATP-binding cassette (ABC) transporter that is required for release of the periplasmic haem chaperone CcmE to the last step of cytochrome c assembly. This ABC transporter is composed of the ABC subunit CcmA, and two membrane proteins, CcmB and CcmC. In the absence of CcmA or CcmB, holo(haem)CcmE binds to CcmC in a stable dead-end complex, indicating high affinity binding of haem to CcmC. Expression of CcmA and CcmB facilitates formation of the CcmA2B1C1 complex and ATP-dependent release of holoCcmE. We propose that the CcmA2B1C1 complex represents a new subgroup within the ABC transporter superfamily that functions to release a chaperone.
authors.affiliation: Washington University, Department of Biology Campus Box 1137, 1 Brookings Drive, St. Louis, MO 63130, USA.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Feissner
authors.forename: Cynthia L
authors.initials: CL
authors.lastname: Richard-Fogal
authors.forename: Elaine R
authors.initials: ER
authors.lastname: Frawley
authors.forename: Robert G
authors.initials: RG
authors.lastname: Kranz
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D001059:Apoproteins / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport; D003574:Cytochrome c Group / Q000096:biosynthesis*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D006418:Heme / Q000378:metabolism*; D006420:Hemeproteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D018832:Molecular Chaperones / Q000378:metabolism*; D010957:Plasmids / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D001059:Apoproteins; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; C118373:CcmA protein, bacteria; C513740:CcmB 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; D018832:Molecular Chaperones; D011993:Recombinant Fusion Proteins; D006418:Heme