This is a family of vitamin-B12 independent methionine synthases or 5-methyltetrahydropteroyltriglutamate--homocysteine methyltransferases, EC:2.1.1.14 from bacteria and plants. Plants are the only higher eukaryotes that have the required enzymes for methionine synthesis [1]. This enzyme catalyses the last step in the production of methionine by transferring a methyl group from 5-methyltetrahydrofolate to homocysteine [1]. The aligned region makes up the carboxy region of the approximately 750 amino acid protein except in some hypothetical archaeal proteins present in the family, where this region corresponds to the entire length. This domain contains the catalytic residues of the enzyme [2].

1: The specific features of methionine biosynthesis and metabolism in plants. Ravanel S, Gakiere B, Job D, Douce R; Proc Natl Acad Sci U S A 1998;95:7805-7812. PMID:9636232

2: Crystal structures of cobalamin-independent methionine synthase complexed with zinc, homocysteine, and methyltetrahydrofolate. Ferrer JL, Ravanel S, Robert M, Dumas R; J Biol Chem 2004;279:44235-44238. PMID:15326182