title: Interaction of holoCcmE with CcmF in heme trafficking and cytochrome c biosynthesis.
abstract: The periplasmic heme chaperone holoCcmE is essential for heme trafficking in the cytochrome c biosynthetic pathway in many bacteria, archaea, and plant mitochondria. This pathway, called system I, involves two steps: (i) formation and release of holoCcmE (by the ABC-transporter complex CcmABCD) and (ii) delivery of the heme in holoCcmE to the putative cytochrome c heme lyase complex, CcmFH. CcmFH is believed to facilitate the final covalent attachment of heme (from holoCcmE) to the apocytochrome c. Although most models for system I propose that holoCcmE delivers heme directly to CcmF, no interaction between holoCcmE and CcmF has been demonstrated. Here, a complex between holoCcmE and CcmF is “trapped”, purified, and characterized. HoloCcmE must be released from the ABC-transporter complex CcmABCD to interact with CcmF, and the holo-form of CcmE interacts with CcmF at levels at least 20-fold higher than apoCcmE. Two conserved histidines (here termed P-His1 and P-His2) in separate periplasmic loops in CcmF are required for interaction with holoCcmE, and evidence that P-His1 and P-His2 function as heme-binding ligands is presented. These results show that heme in holoCcmE is essential for complex formation with CcmF and that the heme of holoCcmE is coordinated by P-His1 and P-His2 within the WWD domain of CcmF. These features are strikingly similar to formation of the CcmC:heme:CcmE ternary complex [Richard-Fogal C, Kranz RG. The CcmC:heme:CcmE complex in heme trafficking and cytochrome c biosynthesis. J Mol Biol 2010;401:350–62] and suggest common mechanistic and structural aspects.
authors: Brian
authors: B
authors: San Francisco
authors: Robert G
authors: RG
authors: Kranz
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism*; D045304:Cytochromes c / Q000096:biosynthesis*; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D005816:Genetic Complementation Test; D006418:Heme / Q000378:metabolism*; D006420:Hemeproteins / Q000378:metabolism*; D020035:Holoenzymes / Q000378:metabolism*; D007093:Imidazoles / Q000378:metabolism; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics; D021381:Protein Transport; D013056:Spectrophotometry, Ultraviolet
chemical_list: D001425:Bacterial Outer Membrane Proteins; C115384:CcmE protein, E coli; D029968:Escherichia coli Proteins; D006420:Hemeproteins; D020035:Holoenzymes; D007093:Imidazoles; D006418:Heme; C029899:imidazole; D045304:Cytochromes c