NqrM (DUF539) protein is required for maturation of bacterial Na+-translocating NADH:quinone oxidoreductaseстатья
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Дата последнего поиска статьи во внешних источниках: 12 июня 2016 г.
Аннотация:Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) catalyzes electron transfer from NADH to ubiquinone in the bacterial respiratory chain, coupled with Na+ translocation across the membrane. Na+-NQR maturation involves covalent attachment of FMN residues, catalyzed by flavin transferase encoded by the nqr-associated apbE gene. Analysis of complete bacterial genomes has revealed another putative gene (duf539, here renamed as nqrM) that usually follows the apbE gene and is only present in Na+-NQR-containing bacteria. Expression of the Vibrio harveyi nqr operon alone or with the associated apbE gene in Escherichia coli, which lacks its own Na+-NQR, resulted in an enzyme incapable of Na+-dependent (d)NADH oxidation. However, fully functional Na+-NQR was restored when these genes were co-expressed with the V. harveyi nqrM gene. Furthermore, nqrM lesions in Klebsiella pneumoniae and V. harveyi prevented production of functional Na+-NQR, which could be recovered by a nqrM-containing plasmid. The Na+-NQR complex isolated from the nqrM-deficient strain of V. harveyi lacks several subunits, indicating that nqrM is necessary for Na+-NQR assembly. The protein product of the nqrM gene, NqrM, contains a single putative transmembrane α-helix and a quad of conserved Cys residues. Mutating one of these residues (Cys33 in V. harveyi NqrM) to Ser completely prevented Na+-NQR maturation, whereas mutating any other Cys residue only decreased the yield of the maturated protein. These findings identify NqrM as the second specific maturation factor of Na+-NQR in proteobacteria, presumably involved in the delivery of Fe to form the (Cys)4[Fe] center between subunits NqrD and NqrE.