PURIFICATION AND MOLECULAR CHARACTERIZATION OF THE ELECTRON-TRANSFER PROTEIN OF METHANESULFONIC-ACID MONOOXYGENASE

A novel serine pathway methylotroph, strain M2, capable of utilizing m ethanesulfonic acid (MSA) as a sole source of carbon and energy was in vestigated, The initial step in the biodegradative pathway of MSA in s train M2 involved an inducible NADH-specific monooxygenase enzyme (MSA MO). Fractionation of MSAMO active cell extracts by ion-exchange chrom atography led to the loss of MSAMO activity, Activity was restored by mixing three distinct protein fractions, designated A, B, and C. Furth er purification to homogeneity of component C indicated that the polyp eptide was acidic, with a pI of 3.9, and contained an iron-sulfur cent er with spectral characteristics similar to those of other proteins co ntaining Rieske [2Fe-2S] centers. The size of the protein subunit and the similarity of the N-terminal sequence to those of ferredoxin compo nents of other oxygenase enzymes have suggested that component C is a specific electron transfer protein of the MSAMO which contains a Riesk e [2Fe-2S] cluster, The gene encoding component C of MSAMO was cloned and sequenced, and the predicted protein sequence was compared with th ose of other Rieske [2Fe-2S]-center-containing ferredoxins, MSAMO appe ars to be a novel combination of oxygenase elements in which an enzyme related to aromatic-ring dioxygenases attacks a one-carbon (C-1) comp ound via monooxygenation.