| |
[摘要]：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 peri-plasmic nitrate respiration and respiratory nitrite ammonification. Knowledge of the structure-function relationships of NapC/NrfH proteins is scarce and only one high-resolution structure (De-sulfovibrio 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 ill one of the four CX2CH haem c-binding motifs is essential for NrfH Maturation ill W succinogenes, and indicate a limited flexibility towards the length and Structure of the transmembrane region. |
|
