THE AMINO-ACID-SEQUENCE OF RHODOBACTER-SPHAEROIDES DIMETHYL-SULFOXIDEREDUCTASE

The complete amino acid sequence of the soluble, monomeric molybdenum- containing enzyme dimethyl sulfoxide reductase from Rhodobacter sphaer oides f sp, denitrificans has been determined using a combination of g as-phase Edman sequencing of isolated peptides and direct sequencing o f 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 through out the sequence and featured regions of sequence corresponding to the prokaryotic molybdopterin-binding signatures 2 and 3. While exhibitin g limited sequence similarity to the corresponding membrane-bound moly bdenum-containing subunit (DmsA) of Escherichia cold dimethyl sulfoxid e reductase, the Rhodobacter sequence showed extensive sequence simila rity to that of the E. coli molybdoprotein, trimethylamine N-oxide red uctase (torA), Comparison with other related prokaryotic molybdenum-co ntaining enzymes indicated the presence of two highly conserved cystei ne residues (Cys-268 and Cys-616) which may function in molybdenum coo rdination. (C) 1995 Academic Press, Inc.