title: Structure of dimeric cytochrome c3 from Desulfovibrio gigas at 1.2 A resolution.
abstract: The structure of dimeric cytochrome c(3) from the sulfate-reducing bacterium Desulfovibrio gigas, diDg, obtained by ab initio methods was further refined to 1.2 A resolution, giving final reliability factors of R(free) = 14.8% and R = 12.4%. This cytochrome is a dimer of tetraheme cytochrome c(3) molecules covalently linked by two solvent-accessible disulfide bridges, a characteristic unique to members of the cytochrome c(3) superfamily. Anisotropic analysis using the semi-rigid TLS method shows different behaviour for analogous loops in each monomer arising from their different packing environments. A detailed sequence and structural comparison with all other known cytochrome c(3) domains in single- and multi-domain cytochromes c(3) shows the presence of structurally conserved regions in this family, despite the high variability of the amino-acid sequence. An internal water molecule is conserved in a common structural arrangement in all c(3) tetraheme domains, indicating a probable electron-transfer pathway between hemes I and II. Unique features of diDg are an internal methionine residue close to heme I and to one of the axial ligands of heme III, where all other structures of the cytochrome c(3) superfamily have a phenylalanine, and a rather unusual CXXXCH heme-binding motif only found so far in this cytochrome.
authors.affiliation: Instituto de Tecnologia Química e Biológica, Oeiras, Portugal.
authors.forename: David
authors.initials: D
authors.lastname: Aragão
authors.forename: Carlos
authors.initials: C
authors.lastname: Frazão
authors.forename: Larry
authors.initials: L
authors.lastname: Sieker
authors.forename: George M
authors.initials: GM
authors.lastname: Sheldrick
authors.forename: Jean
authors.initials: J
authors.lastname: LeGall
authors.forename: Maria Arménia
authors.initials: MA
authors.lastname: Carrondo
mesh_terms: D000595:Amino Acid Sequence; D016880:Anisotropy; D003460:Crystallization; D018360:Crystallography, X-Ray; D003574:Cytochrome c Group / Q000737:chemistry*; D003901:Desulfovibrio / Q000201:enzymology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D014961:X-Ray Diffraction
chemical_list: D003574:Cytochrome c Group; C017165:cytochrome c(3)