title: Crystal structure of the 16 heme cytochrome from Desulfovibrio gigas: a glycosylated protein in a sulphate-reducing bacterium.
abstract: Sulphate-reducing bacteria have a wide variety of periplasmic cytochromes involved in electron transfer from the periplasm to the cytoplasm. HmcA is a high molecular mass cytochrome of 550 amino acid residues that harbours 16 c-type heme groups. We report the crystal structure of HmcA isolated from the periplasm of Desulfovibrio gigas. Crystals were grown using polyethylene glycol 8K and zinc acetate, and diffracted beyond 2.1 A resolution. A multiple-wavelength anomalous dispersion experiment at the iron absorption edge enabled us to obtain good-quality phases for structure solution and model building. DgHmcA has a V-shape architecture, already observed in HmcA isolated from Desulfovibrio vulgaris Hildenborough. The presence of an oligosaccharide molecule covalently bound to an Asn residue was observed in the electron density maps of DgHmcA and confirmed by mass spectrometry. Three modified monosaccharides appear at the highly hydrophobic vertex, possibly acting as an anchor of the protein to the cytoplasmic membrane.
authors.affiliation: REQUIMTE, CQFB, Departamento de Química, FCT-UNL, 2829-516 Caparica, Portugal.
authors.forename: Teresa
authors.initials: T
authors.lastname: Santos-Silva
authors.forename: João Miguel
authors.initials: JM
authors.lastname: Dias
authors.forename: Alain
authors.initials: A
authors.lastname: Dolla
authors.forename: Marie-Claire
authors.initials: MC
authors.lastname: Durand
authors.forename: Luísa L
authors.initials: LL
authors.lastname: Gonçalves
authors.forename: Jorge
authors.initials: J
authors.lastname: Lampreia
authors.forename: Isabel
authors.initials: I
authors.lastname: Moura
authors.forename: Maria João
authors.initials: MJ
authors.lastname: Romão
mesh_terms: D000595:Amino Acid Sequence; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D003580:Cytochromes / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D045286:Desulfovibrio gigas / Q000737:chemistry* / Q000378:metabolism*; D006031:Glycosylation; D006418:Heme / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D055672:Static Electricity; D040681:Structural Homology, Protein
chemical_list: D003580:Cytochromes; D006418:Heme