Probably harbors a corrinoid prosthetic group and acts as a methyl group carrier between MtgB and MtgA. A methyl group from glycine betaine is likely first transferred to the corrinoid prosthetic group of the enzyme by MtgB, and then transferred to tetrahydrofolate (THF) by MtgA. The methyl group may then be ultimately converted to carbon dioxide, and its oxidation would also provide reducing equivalents for anaerobic respiration. Thus, may function in the pathway that allows anaerobic methylotrophic growth of D.hafniense using glycine betaine. Belongs to the methylamine corrinoid protein family.