Expression and mutagenesis of the NqrC subunit of the NQR respiratory Na+ pump from Vibrio cholerae with covalently attached FMN

The Na+-translocating NADH:quinone oxidoreductase (Na+-NQR) is present in t he membranes of a number of marine bacteria and pathogenic bacteria. Two of the six subunits of the Na+-NQR, NqrB and NqrC, have been previously shown to contain covalently bound flavin adenine mononucleotide (FMN). In the cu rrent work, the cloning of nqrC from Vibrio cholerae is reported, The gene has been expressed in V. cholerae and shown to contain one equivalent of co valently bound FMN. In contrast, no covalent flavin was detected when threo nine-225 was replaced by leucine, The data show that the FMN attachment doe s not require assembly of the enzyme and are consistent with the unusual th reonine attachment site. (C) 2001 Federation of European Biochemical Societ ies. Published by Elsevier Science B.V. All rights reserved.