Harbors a corrinoid prosthetic group and acts as a methyl group carrier in methanogenesis in the methanol pathway. The methyl group of methanol is first transferred to the corrinoid prosthetic group of MtaC in the cob(I)amide oxidation state. This reaction is mediated by MtaB. The methyl group from MtaC is then transferred to coenzyme M by MtaA. Heterotetramer, composed of 2 MtaB and 2 MtaC subunits. Belongs to the methylamine corrinoid protein family.