5-Methyltetrahydropteroyltriglutamate—homocysteine S-methyltransferase

In enzymology, a 5-methyltetrahydropteroyltriglutamate—homocysteine S-methyltransferase (EC 2.1.1.14) is an enzyme that catalyzes the chemical reaction

5-methyltetrahydropteroyltri-L-glutamate + L-homocysteine

\rightleftharpoons

tetrahydropteroyltri-L-glutamate + L-methionine

Thus, the two substrates of this enzyme are 5-methyltetrahydropteroyltri-L-glutamate and L-homocysteine, whereas its two products are tetrahydropteroyltri-L-glutamate and L-methionine. This enzyme participates in methionine metabolism. It has 2 cofactors: orthophosphate, and zinc.

Nomenclature

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.

Structure

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-glutamic acid and the C-terminal barrel binds homocysteine. Homocysteine is coordinated to a zinc ion, as initially suggested by spectroscopy and mutagenesis .

References

Pejchal R, Ludwig ML (February 2005). "Cobalamin-independent methionine synthase (MetE): a face-to-face double barrel that evolved by gene duplication". PLOS Biology. 3 (2): e31. doi:10.1371/journal.pbio.0030031. PMC 539065. PMID 15630480.

Guest JR, Friedman S, Foster MA, Tejerina G, Woods DD (September 1964). "Transfer of the methyl group from N5-methyltetrahydrofolates to homocysteine in Escherichia coli" (Free full text). The Biochemical Journal. 92 (3): 497–504. doi:10.1042/bj0920497. PMC 1206090. PMID 5319972.
Whitfield CD, Steers EJ, Weissbach H (January 1970). "Purification and properties of 5-methyltetrahydropteroyltriglutamate-homocysteine transmethylase" (Free full text). The Journal of Biological Chemistry. 245 (2): 390–401. doi:10.1016/S0021-9258(18)63404-0. PMID 4904482.
Eichel J, González JC, Hotze M, Matthews RG, Schröder J (June 1995). "Vitamin-B12-independent methionine synthase from a higher plant (Catharanthus roseus). Molecular characterization, regulation, heterologous expression, and enzyme properties". European Journal of Biochemistry. 230 (3): 1053–8. doi:10.1111/j.1432-1033.1995.1053g.x. PMID 7601135. Archived from the original (Free full text) on 2013-01-05.
González JC, Peariso K, Penner-Hahn JE, Matthews RG (September 1996). "Cobalamin-independent methionine synthase from Escherichia coli: a zinc metalloenzyme". Biochemistry. 35 (38): 12228–34. doi:10.1021/bi9615452. PMID 8823155.
Peariso K, Goulding CW, Huang S, Matthews RG, Penner-Hahn JE (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 (33): 8410–8416. doi:10.1021/ja980581g.

Transferase: one carbon transferases (EC 2.1)

2.1.1: Methyl-

N-	Histamine N-methyltransferase Phenylethanolamine N-methyltransferase Amine N-methyltransferase Phosphatidylethanolamine N-methyltransferase
O-	5-hydroxyindole-O-methyltransferase/Acetylserotonin O-methyltransferase Catechol-O-methyl transferase
Homocysteine	Betaine-homocysteine methyltransferase Homocysteine methyltransferase Methionine synthase
Other	Phosphatidyl ethanolamine methyltransferase DNMT3B Histone methyltransferase Thymidylate synthase DNA methyltransferase Thiopurine methyltransferase Cyclopropane-fatty-acyl-phospholipid synthase

2.1.2: Hydroxymethyl-,
Formyl- and Related

Hydroxymethyltransferase	Serine hydroxymethyltransferase 3-methyl-2-oxobutanoate hydroxymethyltransferase
Formyltransferase	Phosphoribosylglycinamide formyltransferase Inosine monophosphate synthase
Other	Glutamate formimidoyltransferase Aminomethyltransferase

2.1.3: Carboxy-
and Carbamoyl

Carboxy	methylmalonyl-CoA carboxytransferase
Carbamoyl	Aspartate carbamoyltransferase Ornithine carbamoyltransferase Oxamate carbamoyltransferase Putrescine carbamoyltransferase 3-hydroxymethylcephem carbamoyltransferase Lysine carbamoyltransferase N-acetylornithine carbamoyltransferase

2.1.4: Amidine

Arginine:glycine amidinotransferase

v t e Enzymes
Activity	Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Diffusion-limited enzyme Cofactor Enzyme catalysis
Regulation	Allosteric regulation Cooperativity Enzyme inhibitor Enzyme activator
Classification	EC number Enzyme superfamily Enzyme family List of enzymes
Kinetics	Enzyme kinetics Eadie–Hofstee diagram Hanes–Woolf plot Lineweaver–Burk plot Michaelis–Menten kinetics
Types	EC1 Oxidoreductases (list) EC2 Transferases (list) EC3 Hydrolases (list) EC4 Lyases (list) EC5 Isomerases (list) EC6 Ligases (list) EC7 Translocases (list)

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Nomenclature

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