The amino acid sequence of Rhodobacter sphaeroides dimethyl sulfoxide reductase

The complete amino acid sequence of the soluble, monomeric molybdenum-containing enzyme dimethyl sulfoxide reductase from Rhodobacter sphaeroides f sp. denitrificans has been determined using a combination of gas-phase Edman sequencing of isolated peptides and direct sequencing of PCR products generated from R. sphaeroides genomic DNA. The protein comprises 777 residues corresponding to an apoenzyme molecular weight of 84,748 Da. The amino acid sequence was rich in Ala and Gly residues which represented 21% of the protein's composition. The DNA sequence was 67% rich in G and C nucleotides. The amino acid sequence contained 10 cysteine residues which were relatively evenly distributed throughout the sequence and featured regions of sequence corresponding to the prokaryotic molybdopterin-binding signatures 2 and 3. While exhibiting limited sequence similarity to the corresponding membrane-bound molybdenum-containing subunit (DmsA) of Escherichia coli dimethyl sulfoxide reductase, the Rhodobacter sequence showed extensive sequence similarity to that of the E. coli molybdoprotein, trimethylamine N-oxide reductase (torA). Comparison with other related prokaryotic molybdenum-containing enzymes indicated the presence of two highly conserved cysteine residues (Cys-268 and Cys-616) which may function in molybdenum coordination.