title: Solution structure and characterization of the heme chaperone CcmE.
abstract: The covalent attachment of the heme cofactor in c-type cytochromes is a surprisingly complex process, which in bacteria involves a number of different proteins. Among the latter, the ccmE gene product is known to perform a key role in the heme delivery pathway in Gram-negative bacteria. The solution structure of the soluble domain of apo-CcmE from Shewanella putrefaciens was determined through NMR spectroscopy on a 13C,15N-labeled sample. The structure is characterized by a compact core with large regions of beta structure, while the N-terminal and C-terminal regions are essentially unstructured. The overall folding is similar to that of the so-called oligo-binding proteins (OB fold). Solvent-exposed aromatic residues, conserved in all CcmE homologues, have been found in the proximity of His131, the putative heme-binding residue, that could have a role in the interaction with heme. No interaction between CcmE and heme, as well as between CcmE and holocytochrome c, could be detected in vitro by electronic spectroscopy or by NMR. The data available suggest that the heme transfer process is likely to involve a heterooligomeric protein complex and occur under a tight enzymatic control.
authors.affiliation: Magnetic Resonance Center, University of Florence, Sesto Fiorentino, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Arnesano
authors.forename: Lucia
authors.initials: L
authors.lastname: Banci
authors.forename: Paul D
authors.initials: PD
authors.lastname: Barker
authors.forename: Ivano
authors.initials: I
authors.lastname: Bertini
authors.forename: Antonio
authors.initials: A
authors.lastname: Rosato
authors.forename: Xun Cheng
authors.initials: XC
authors.lastname: Su
authors.forename: Maria Silvia
authors.initials: MS
authors.lastname: Viezzoli
mesh_terms: D001226:Aspartate-tRNA Ligase / Q000737:chemistry; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D018360:Crystallography, X-Ray; D004268:DNA-Binding Proteins / Q000737:chemistry; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics; D029968:Escherichia coli Proteins; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006420:Hemeproteins / Q000737:chemistry* / Q000235:genetics; D007700:Kinetics; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry*; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D051716:Replication Protein A; D020592:Shewanella / Q000737:chemistry*; D012996:Solutions
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; C115384:CcmE protein, E coli; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D006420:Hemeproteins; D018832:Molecular Chaperones; D051716:Replication Protein A; D012996:Solutions; D006418:Heme; D001226:Aspartate-tRNA Ligase