title: Structure of a novel c7-type three-heme cytochrome domain from a multidomain cytochrome c polymer.
abstract: The structure of a novel c(7)-type cytochrome domain that has two bishistidine coordinated hemes and one heme with histidine, methionine coordination (where the sixth ligand is a methionine residue) was determined at 1.7 A resolution. This domain is a representative of domains that form three polymers encoded by the Geobacter sulfurreducens genome. Two of these polymers consist of four and one protein of nine c(7)-type domains with a total of 12 and 27 hemes, respectively. Four individual domains (termed A, B, C, and D) from one such multiheme cytochrome c (ORF03300) were cloned and expressed in Escherichia coli. The domain C produced diffraction quality crystals from 2.4 M sodium malonate (pH 7). The structure was solved by MAD method and refined to an R-factor of 19.5% and R-free of 21.8%. Unlike the two c(7) molecules with known structures, one from G. sulfurreducens (PpcA) and one from Desulfuromonas acetoxidans where all three hemes are bishistidine coordinated, this domain contains a heme which is coordinated by a methionine and a histidine residue. As a result, the corresponding heme could have a higher potential than the other two hemes. The apparent midpoint reduction potential, E(app), of domain C is -105 mV, 50 mV higher than that of PpcA.
authors.affiliation: Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA.
authors.forename: P Raj
authors.initials: PR
authors.lastname: Pokkuluri
authors.forename: Yuri Y
authors.initials: YY
authors.lastname: Londer
authors.forename: Norma E C
authors.initials: NE
authors.lastname: Duke
authors.forename: Jill
authors.initials: J
authors.lastname: Erickson
authors.forename: Miguel
authors.initials: M
authors.lastname: Pessanha
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Salgueiro
authors.forename: Marianne
authors.initials: M
authors.lastname: Schiffer
mesh_terms: D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D003574:Cytochrome c Group / Q000737:chemistry* / Q000235:genetics; D045287:Desulfuromonas / Q000737:chemistry / Q000235:genetics; D015870:Gene Expression; D045302:Geobacter / Q000737:chemistry / Q000235:genetics; D006418:Heme / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D017186:Titrimetry
chemical_list: D003574:Cytochrome c Group; C114913:cytochrome C7; D006418:Heme