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, likely because of its higher Lewis acidity, which is important for the catalytic activity of the enzyme.