title: X-ray structure of the membrane-bound cytochrome c quinol dehydrogenase NrfH reveals novel haem coordination.
abstract: Oxidation of membrane-bound quinol molecules is a central step in the respiratory electron transport chains used by biological cells to generate ATP by oxidative phosphorylation. A novel family of cytochrome c quinol dehydrogenases that play an important role in bacterial respiratory chains was recognised in recent years. Here, we describe the first structure of a cytochrome from this family, NrfH from Desulfovibrio vulgaris, which forms a stable complex with its electron partner, the cytochrome c nitrite reductase NrfA. One NrfH molecule interacts with one NrfA dimer in an asymmetrical manner, forming a large membrane-bound complex with an overall alpha(4)beta(2) quaternary arrangement. The menaquinol-interacting NrfH haem is pentacoordinated, bound by a methionine from the CXXCHXM sequence, with an aspartate residue occupying the distal position. The NrfH haem that transfers electrons to NrfA has a lysine residue from the closest NrfA molecule as distal ligand. A likely menaquinol binding site, containing several conserved and essential residues, is identified.
authors.affiliation: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, ITQB-UNL, Oeiras, Portugal.
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: Rodrigues
authors.forename: Tânia F
authors.initials: TF
authors.lastname: Oliveira
authors.forename: Inês A C
authors.initials: IA
authors.lastname: Pereira
authors.forename: Margarida
authors.initials: M
authors.lastname: Archer
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D001665:Binding Sites; D002462:Cell Membrane / Q000201:enzymology*; D018360:Crystallography, X-Ray; D045304:Cytochromes c / Q000737:chemistry*; D016969:Desulfovibrio vulgaris / Q000201:enzymology*; D006418:Heme / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000737:chemistry*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D055672:Static Electricity
chemical_list: D001426:Bacterial Proteins; D006418:Heme; D045304:Cytochromes c; D010088:Oxidoreductases