This family of proteins is found in bacteria and archaea. Proteins in this family are approximately 460 amino acids in length. MtaB folds as a TIM barrel and contains a novel zinc-binding motif. Zinc(II) lies at the bottom of a funnel formed at the C-terminal beta-barrel end and ligates to two cysteinyl sulfurs (Cys-220 and Cys-269) and one carboxylate oxygen (Glu-164). The function of this protein is to catalyse the cleavage of the C O bond in methanol by an SN2 mechanism. It complexes with MtaA and MtaC to perform this function.

1: Insight into the mechanism of biological methanol activation based on the crystal structure of the methanol-cobalamin methyltransferase complex. Hagemeier CH, Krer M, Thauer RK, Warkentin E, Ermler U; Proc Natl Acad Sci U S A. 2006;103:18917-18922. PMID:17142327