5,10-methylenetetrahydrofolate structure

Methylenetetrahydrofolate reductase (MTHFR) catalyzes the NAD(P)H-dependent reduction of 5,10-methylenetetrahydrofolate (CH2-THF) to 5-methyltetrahydrofolate (CH3-THF). CH3-THF then serves as a methyl donor for the synthesis of methionine. The MTHFR proteins and genes from mammalian liver and E. coli have been characterized,12"15 and MTHFR genes have been identified in S. cerevisiae16 and other organisms. The MTHFR of E. coli (MetF) is a homotetramer of 33-kDa subunits that prefers NADH as reductant,12 whereas mammalian MTHFRs are homodimers of 77-kDa subunits that prefer NADPH and are allosterically inhibited by AdoMet.13,14 Mammalian MTHFRs have a two-domain structure the amino-terminal domain shows 30% sequence identity to E. coli MetF, and is catalytic the carboxyterminal domain has been implicated in AdoMet-mediated inhibition of enzyme activity.13,14... 

GOYETTE, P., PAI, A., MILOS, R., FROSST, P., TRAN, P., CHEN, Z., CHAN, M.,.ROZEN, R., Gene structure of human and mouse methylenetetrahydrofolate reductase (MTHFR), Mamm. Genome, 1998,9,652-656. 

Guenther BD, Sheppard CA, Tran P, Rozen R, Matthews RG, and Ludwig ML (1999) The structure and properties of methylenetetrahydrofolate reductase from Escherichia coK suggest how folate ameliorates human hyperhomocysteinemia. Nature Structural Biology S, 359-65. 

Fig. 1. Chemical structure of cofactors (a) NAD(P)+ and (b) NADH(P), with R = H is NAD+ or NADH, and R = P is NADP+ or NADPH, (c) Flavin mononucleotide (FMN), (d) Flavin adenine dinucleotide (FAD), (e)Tetrahydrofolate, (f) 10-formyltetrahydro-folic acid, (g) 5-10 methylenetetrahydrofolic acid,...

Fluorodeoxyuridine monophosphate (FdUMP) is a molecule that is a mechanism-based inhibitor. Irreversible binding of FdUMP to thymidylate synthase occurs only in the presence of 5,10-methyl enetetrahydrofolate. Crystallographic analysis of thymidylate synthase with dUMP and an analog of 5,10-methylenetetrahydrofolate (that could not be acted on by the enzyme) reveals that thymidylate synthase normally makes a transient covalent bond in the process of catalysis of the reaction. Apparently FdUMP s structure traps the enzyme-substrate covalent bond and prevents it from breaking down. 

D. A. Matthews, K. App lt, S. J. Oadey, and N. H. Xuoi J. Mot Biol., 214,923 (1990). Stereochemical Mechanism of Action for Thymidylate Synthase Based on the X-Ray Structure of the Covalent Inhibitory Ternary Complex with 5-Fluoro-2 -deQxyuridylate and 5,10-Methylenetetrahydrofolate. 

---