title: Variants of the tetrahaem cytochrome c quinol dehydrogenase NrfH characterize the menaquinol-binding site, the haem c-binding motifs and the transmembrane segment.
abstract: Members of the NapC/NrfH family are multihaem c-type cytochromes that exchange electrons with oxidoreductases situated at the outside of the cytoplasmic membrane or in the periplasmic space of many proteobacteria. They form a group of membrane-bound quinol dehydrogenases that are essential components of several electron transport chains, for example those of periplasmic nitrate respiration and respiratory nitrite ammonification. Knowledge of the structure-function relationships of NapC/NrfH proteins is scarce and only one high-resolution structure (Desulfovibrio vulgaris NrfH) is available. In the present study, several Wolinella succinogenes mutants that produce variants of NrfH, the membrane anchor of the cytochrome c nitrite reductase complex, were constructed and characterized in order to improve the understanding of the putative menaquinol-binding site, the maturation and function of the four covalently bound haem c groups and the importance of the N-terminal transmembrane segment. Based on amino acid sequence alignments, a homology model for W. succinogenes NrfH was constructed that underlines the overall conservation of tertiary structure in spite of a low sequence homology. The results support the proposed architecture of the menaquinol-binding site in D. vulgaris NrfH, demonstrate that each histidine residue arranged in one of the four CX(2)CH haem c-binding motifs is essential for NrfH maturation in W. succinogenes, and indicate a limited flexibility towards the length and structure of the transmembrane region.
authors.affiliation: Institut für Molekulare Biowissenschaften, Johann Wolfgang Goethe-Universität, Max-von-Laue-Str. 9, D-60438 Frankfurt am Main, Germany.
authors.forename: Melanie
authors.initials: M
authors.lastname: Kern
authors.forename: Oliver
authors.initials: O
authors.lastname: Einsle
authors.forename: Jörg
authors.initials: J
authors.lastname: Simon
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D002478:Cells, Cultured; D045304:Cytochromes c / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016969:Desulfovibrio vulgaris / Q000201:enzymology / Q000235:genetics; D014644:Genetic Variation / Q000235:genetics*; D006418:Heme / Q000031:analogs & derivatives* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009284:Naphthols / Q000737:chemistry / Q000378:metabolism; D009565:Nitrate Reductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013729:Terpenes / Q000737:chemistry / Q000378:metabolism; D016968:Wolinella / Q000201:enzymology
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; D009284:Naphthols; D013729:Terpenes; C031690:heme C; C066500:menaquinol 6; D006418:Heme; D045304:Cytochromes c; D010088:Oxidoreductases; D009565:Nitrate Reductases