CIMS - Cobalamine-independent methonine synthase, or MetE, N-terminal domain_like. Many members have been characterized as 5-methyltetrahydropteroyltriglutamate-homocysteine methyltransferases, EC:2.1.1.14, mostly from bacteria and plants. This enzyme catalyses the last step in the production of methionine by transferring a methyl group from 5-methyltetrahydrofolate to L-homocysteine without using an intermediate methyl carrier. The active enzyme has a dual (beta-alpha)8-barrel structure, and this model covers the N-terminal barrel, and a few single-barrel sequences most similar to the N-terminal barrel. It is assumed that the homologous N-terminal barrel has evolved from the C-terminus via gene duplication and has subsequently lost binding sites, and it seems as if the two barrels forming the active enzyme may sometimes reside on different polypeptides. The C-terminal domain incorporates the Zinc ion, which binds and activates homocysteine. Side chains from both barrels contribute to the binding of the folate substrate.
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