Molecular structure and gene analysis of Ce3+-induced methanol dehydrogenase of Bradyrhizobium sp. MAFF211645

The molecular structure and nucleotide sequence of Ce(3+)-induced methanol dehydrogenase (MDH) of Bradyrhizobium sp. MAFF211645 were investigated. The addition of 30 μM Ce(3+) to 1/10 nutrient broth containing 0.5% methanol remarkably increased MDH activity. Furthermore, La(3+) increased MDH activity, but other heavier rare earth and metal elements did not have the same effect. MDH increased by Ce(3+) was purified by sequential column chromatography, and the purified MDH migrated as a single band with an apparent molecular weight of 68 kDa on SDS-PAGE. The apparent molecular weight of native MDH was estimated to be 108,000 by gel chromatography. The MDH was comprised of two identical subunits. N-terminal 23-amino acid sequence, 1-NDELHKMAQNPKDWVMPAGDYAN-23, of the purified MDH exhibited 91.3% identity to that of the MDH large subunit-like protein encoded by mxaF' of Bradyrhizobium japonicum USDA110. Nucleotide sequencing of the MDH gene of strain MAFF211645 yielded a deduced amino acid sequence comprising 601 amino acid residues, an N-terminal signal peptide, and a mature MDH comprising 578 amino acid residues with a predicted molecular mass of 62,918 Da. Further analysis of the deduced amino acid sequence of mature MDH revealed that the functional amino acids in its active site, such as two adjacent Cys residues, and bacterial quinoprotein signatures 1 and 2 were conserved. These results indicate that Ce(3+)-induced MDH encoded by mxaF' may be involved in methanol metabolism in Bradyrhizobium sp. MAFF211645.