Lanthanide-dependent methanol dehydrogenase from the legume symbiotic nitrogen-fixing bacterium Bradyrhizobium diazoefficiens strain USDA110

Abstract The legume symbiotic nitrogen-fixing bacterium, B. diazoefficiens strain USDA110, utilizes methanol for growth in the presence of light lanthanides, such as La 3+ , Ce 3+ , Pr 3+ or Nd 3+ , and its cells possess significant methanol dehydrogenase (MDH) activity. We purified MDH to homogeneity from B. diazoefficiens strain USDA110 grown in a methanol/Ce 3+ medium; the protein was identified as XoxF5-type MDH (blr6213). The purified XoxF contained 0.58 cerium atoms per enzyme subunit. Moreover, the in-solution structure of XoxF was analyzed by small angle X-ray scattering (SAXS) analysis; the radius of gyration ( R g ) and maximum particle dimension ( D max ) of XoxF were calculated to be 32.3 and 96.8 A, respectively, suggesting that XoxF adopts a dimer structure in solution. These results show that B. diazoefficiens strain USDA110 has XoxF, a lanthanides-dependent MDH, which has methanol oxidation activity and is induced by methanol/lanthanaides, and that lanthanide is one of the important factors in methanol utilization by the strain.