Molecular analysis of a novel methanesulfonic acid monooxygenase from the methylotroph Methylosulfonomonas methylovora

Methylosulfonomonas methylovora M2 is an unusual gram-negative methylotroph ic bacterium that can grow on methanesulfonic acid (MSA) as the sole source of carbon and energy, Oxidation of MSA by this bacterium is carried out by a multicomponent MSA monooxygenase (MSAMO). Cloning and sequencing of a 7. 5-kbp,sphI fragment of chromosomal DNA revealed four tightly linked genes e ncoding this no,el monooxygenase, Analysis of the deduced MSAMO polypeptide sequences indicated that the enzyme contains a two-component hydroxylase o f the mononuclear-iron-center type, The large subunit of the hydroxylase, M smA (48 kDa), contains a typical Rieske-type [2Fe-2S] center with an unusua l iron-binding motif and, together with the small subunit of the hydroxylas e, MsmB (20 kDa), showed a high degree of identity with a number of dioxyge nase enzymes. However, the other components of the MSAMO, MsmC, the ferredo xin component, and MsmD, the reductase, more closely resemble those found i n other classes of oxygenases. MsmC has a high degree of identity to ferred oxins from toluene and methane monooxygenases, which are enzymes characteri zed by possessing hydroxylases containing mu-oxo bridge binuclear iron cent ers. MsmD is a reductase of 38 kDa with a typical chloroplast-like [2Fe-2S] center and conserved flavin adenine dinucleotide- and NAD-binding motifs a nd is similar to a number of mono- and dioxygenase reductase components. Pr eliminary analysis of the genes encoding MSAMO from a marine MSA-degrading bacterium, Marinosulfonomonas methylotropha, revealed the presence of msm g enes highly related to those found in Methylosulfonomonas, suggesting that MSAMO is a no,el type of oxygenase that may be conserved in all MSA-utilizi ng bacteria.