Preference for particular lanthanide species and thermal stability of XoxFs in Methylorubrum extorquens strain AM1.

XoxF-type methanol dehydrogenase was recently found to be lanthanide-dependent, while its counterpart MxaF is Ca2+-dependent. The lanthanide (Ln) series consists of 15 different elements, all of which exist in nature, although at different relative abundances. XoxF from Methylorubrum extorquens strain AM1 has been shown to be induced by four light Ln species (La3+ to Nd3+). The preference of XoxFs for certain co-existing Ln species and the catalytic activity and stability of XoxF metallated with different Ln species have not been well investigated. In this study, we found that (i) strain AM1 cells preferentially utilize La3+ rather than Nd3+ for growth, (ii) XoxF purified from cells grown with a La3+ and Nd3+ mixture contained a larger proportion of La3+, and (iii) La3+-metallated XoxF has higher activity and thermal stability than Nd3+-metallated XoxF, although (iv) both enzymes showed unchanged surface charges. Thermal shift assay in particular revealed that metallation affects the temperature for subunit denaturation but not for subunit dissociation. We concluded that, although La3+ and Nd3+ have similar distributions in nature, XoxF could chose La3+ preferentially.