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

The legume symbiotic nitrogen-fixing bacterium, B. diazoefficiens strain USDA110, utilizes methanol for growth in the presence of light lanthanides, such as La³⁺, Ce³⁺, Pr³⁺ or Nd³⁺, and its cells possess significant methanol dehydrogenase (MDH) activity. We purified MDH to homogeneity from B. diazoefficiens strain USDA110 grown in a methanol/Ce³⁺ 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 Å, 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.