Variants of the tetrahaem cytochrome c quinol dehydrogenase NrfH characterize the menaquinol binding site, the haem c binding motifs and the transmembrane segment
Résumé
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 on structure/function relationships of NapC/NrfH proteins is scarce and only one high-resolution structure (Desulfovibrio vulgaris NrfH) is available. In this 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 CX2CH haem c binding motifs is essential for NrfH maturation in W. succinogenes and indicate a limited flexibility toward the length and structure of the transmembrane region.
Origine : Fichiers produits par l'(les) auteur(s)
Loading...