This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is 5-methyltetrahydropteroyltri-L-glutamate:L-homocysteine S-methyltransferase. Other names in common use include tetrahydropteroyltriglutamate methyltransferase, homocysteine methylase, methyltransferase, tetrahydropteroylglutamate-homocysteine transmethylase, methyltetrahydropteroylpolyglutamate:homocysteine methyltransferase, cobalamin-independent methionine synthase, methionine synthase (cobalamin-independent), and MetE. This enzyme participates in methionine metabolism. It has 2 cofactors: orthophosphate, and zinc.
As of late 2007, 9 structures have been solved for this class of enzymes, with PDB accession codes 1T7L, 1U1H, 1U1J, 1U1U, 1U22, 1XDJ, 1XPG, 1XR2, and 2NQ5. The enzyme from Escherichia coli consists of two alpha8-beta8 (TIM) barrels positioned face to face and thought to have evolved by gene duplication. The active site lies between the tops of the two barrels, the N-terminal barrel binds 5-methyltetrahydropteroyltri-L-glutamatic acid and the C-terminal barrel binds homocysteine. Homocysteine is coordinated to a zinc ion, as initially suggested by spectroscopy and mutagenesis Gonzalez JC, Peariso K, Penner-Hahn JE, Matthews RG, JC (Sep 1996). "Cobalamin-independent methionine synthase from Escherichia coli: a zinc metalloenzyme". Biochemistry.35 (38): 12228–34. doi:10.1021/bi9615452. ISSN0006-2960. PMID8823155..
^Pejchal, Robert; Martha L. Ludwig (2005). "Cobalamin-independent methionine synthase (MetE): a face-to-face double barrel that evolved by gene duplication". PLOS Biology3 (2). doi:10.1371.
Guest JR, Friedman S, Foster MA, Tejerina G, Woods DD, JR (Sep 1964). "Transfer of the methyl group from N5-methyltetrahydrofolates to homocysteine in Escherichia coli". Biochem. J. (Free full text|format= requires |url= (help)) 92 (3): 497–504. ISSN0264-6021. PMC1206090. PMID5319972.
Gonzalez JC, Peariso K, Penner-Hahn JE, Matthews RG, JC (Sep 1996). "Cobalamin-independent methionine synthase from Escherichia coli: a zinc metalloenzyme". Biochemistry.35 (38): 12228–34. doi:10.1021/bi9615452. ISSN0006-2960. PMID8823155.
Penner-Hahn JE; Goulding, Celia W.; Huang, Sha; Matthews, Rowena G.; Penner-Hahn, James E. (1998). "Characterization of the zinc binding site in methionine synthase enzymes of Escherichia coli: The role of zinc in the methylation of homocysteine". J. Am. Chem. Soc.120: 8410–8416. doi:10.1021/ja980581g.