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methylene tetrahydrofolate reductase
Ribbon diagram of the active site of E. coli MTHFR. The flavin cofactor (top) is shown interacting with the bound substrate NADH.
Identifiers
EC no.	1.5.1.20
CAS no.	9028-69-7
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDB PDBe PDBsum
Gene Ontology	AmiGO / QuickGO
Search PMC articles PubMed articles NCBI proteins

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Methylenetetrahydrofolate reductase (MTHFR) is an enzyme that in humans is encoded by the MTHFR gene. Methylenetetrahydrofolate reductase catalyzes the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, a cosubstrate for homocysteine remethylation to methionine. Genetic variation in this gene influences susceptibility to occlusive vascular disease, neural tube defects, colon cancer and acute leukemia, and mutations in this gene are associated with methylenetetrahydrofolate reductase deficiency.

Biochemistry

MTHFR irreversibly reduces 5,10-methylenetetrahydrofolate (substrate) to 5-methyltetrahydrofolate (product).

• 5,10-methylenetetrahydrofolate is used to convert dUMP to dTMP for de novo thymidine synthesis.
• 5-Methyltetrahydrofolate is used to convert homocysteine (a potentially toxic amino acid) to methionine by the enzyme methionine synthase. (Note that homocysteine can also be converted to methionine by the folate-independent enzyme betaine-homocysteine methyltransferase (BHMT))

MTHFR contains a bound flavin cofactor and uses NAD(P)H as the reducing agent.

Structure

Mammalian MTHFR is composed of an N-terminal catalytic domain and a C-terminal regulatory domain. MTHFR has at least two promoters and two isoforms (70 kDa and 77 kDa).

Regulation

MTHFR activity may be inhibited by binding of dihydrofolate (DHF) and S-adenosylmethionine (SAM, or AdoMet). MTHFR can also be phosphorylated - this decreases its activity by ~20% and allows it to be more easily inhibited by SAM.

Interactive pathway map

Click on genes, proteins and metabolites below to link to respective articles.

1. The interactive pathway map can be edited at WikiPathways: "FluoropyrimidineActivity_WP1601".

Genetics

The enzyme is coded by the gene with the symbol MTHFR on chromosome 1 location p36.3 in humans. There are DNA sequence variants (genetic polymorphisms) associated with this gene. In 2000 a report brought the number of polymorphisms up to 24. Two of the most investigated are C677T (rs1801133) and A1298C (rs1801131) single nucleotide polymorphisms (SNP).

C677T SNP (AlaVal)

The MTHFR nucleotide at position 677 in the gene has two possibilities: C (cytosine) or T (thymine). C at position 677 (leading to an alanine at amino acid 222) is the normal allele. The 677T allele (leading to a valine substitution at amino acid 222) encodes a thermolabile enzyme with reduced activity.

Individual with two copies of 677C (677CC) have the "normal" or "wildtype" genotype. 677TT individuals (homozygous) are said to have mild MTHFR deficiency. 677CT individuals (heterozygotes) are almost the same as normal individuals because the normal MTHFR can make up for the thermolabile MTHFR. About ten percent of the North American population are T-homozygous for this polymorphism. There is ethnic variability in the frequency of the T allele – frequency in Mediterranean/Hispanics is greater than the frequency in Caucasians which, in turn, is greater than in Africans/African-Americans.

The degree of enzyme thermolability (assessed as residual activity after heat inactivation) is much greater in 677TT individuals (18-22%) compared with 677CT (56%) and 677CC (66-67%). Individuals of 677TT are predisposed to mild hyperhomocysteinemia (high blood homocysteine levels), because they have less active MTHFR available to produce 5-methyltetrahydrofolate (which is used to decrease homocysteine). Low dietary intake of the vitamin folic acid can also cause mild hyperhomocysteinemia.

Low folate intake affects individuals with the 677TT genotype to a greater extent than those with the 677CC/CT genotypes. 677TT (but not 677CC/CT) individuals with lower plasma folate levels are at risk for elevated plasma homocysteine levels. In studies of human recombinant MTHFR, the protein encoded by 677T loses its FAD cofactor three times faster than the wild-type protein. 5-Methyl-THF slows the rate of FAD release in both the wild-type and mutant enzymes, although it is to a much greater extent in the mutant enzyme.Cite error: The <ref> tag has too many names (see the help page). 677TT individuals are at a decreased risk for certain leukemias and colon cancer.

Mutations in the MTHFR gene could be one of the factors leading to increased risk of developing schizophrenia. Schizophrenic patients having the risk allele (T\T) show more deficiencies in executive function tasks.

A1298C SNP (GluAla)

At nucleotide 1298 of the MTHFR, there are two possibilities: A or C. 1298A (leading to a Glu at amino acid 429) is the most common while 1298C (leading to an Ala substitution at amino acid 429) is less common. 1298AA is the "normal" homozygous, 1298AC the heterozygous, and 1298CC the homozygous for the "variant". In studies of human recombinant MTHFR, the protein encoded by 1298C cannot be distinguished from 1298A in terms of activity, thermolability, FAD release, or the protective effect of 5-methyl-THF. The C mutation does not appear to affect the MTHFR protein. It does not result in thermolabile MTHFR and does not appear to affect homocysteine levels.

Compound Heterozygotes

Mutations at 677 and 1298 are different locations; however, they are both in the 'same' gene: MTHFR. Some studies have shown that the MTHFR protein in people with the genotype 677CT 1298AC does its job a bit less well than the normal MTHFR.

Severe MTHFR deficiency

Severe MTHFR deficiency is rare (about 50 cases worldwide) and caused by mutations resulting in 0-20% residual enzyme activity. Patients exhibit developmental delay, motor and gait dysfunction, seizures, and neurological impairment and have extremely high levels of homocysteine in their plasma and urine as well as low to normal plasma methionine levels.

Reaction schematic and folate pathway

MTHFR = methylenetetrahydrofolate reductase		DHF = dihydrofolate	THF = tetrahydrofolate
5,10-methylene-THF = 5,10-methylenetetrahydrofolate	5-methyl-THF = 5-methyltetrahydrofolate	MTR = methionine synthase	SAH = S-adenosylhomocysteine
NADPH = reduced form of Nicotinamide adenine dinucleotide phosphate	NADP = oxidized form of Nicotinamide adenine dinucleotide phosphate	SAM = S-Adenosyl methionine	TS = thymidylate synthase

As a drug target

Inhibitors of MTHFR or antisense knockdown of the expression of the enzyme has been proposed as a treatment for cancer.

References

1. PDB: 1ZPT​; Pejchal R, Sargeant R, Ludwig ML (2005). "Structures of NADH and CH3-H4folate complexes of Escherichia coli methylenetetrahydrofolate reductase reveal a spartan strategy for a ping-pong reaction". Biochemistry. 44 (34): 11447–57. doi:10.1021/bi050533q. PMID 16114881.{{cite journal}}: CS1 maint: multiple names: authors list (link)
2. Goyette P, Sumner JS, Milos R, Duncan AM, Rosenblatt DS, Matthews RG, Rozen R (1994). "Human methylenetetrahydrofolate reductase: isolation of cDNA, mapping and mutation identification". Nat. Genet. 7 (2): 195–200. doi:10.1038/ng0694-195. PMID 7920641. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
3. "Entrez Gene: MTHFR methylenetetrahydrofolate reductase (NAD(P)H)".
4. Födinger M, Hörl WH, Sunder-Plassmann G (2000). "Molecular biology of 5,10-methylenetetrahydrofolate reductase". J Nephrol. 13 (1): 20–33. PMID 10720211.{{cite journal}}: CS1 maint: multiple names: authors list (link)
5. Tran P, Leclerc D, Chan M; et al. (2002). "Multiple transcription start sites and alternative splicing in the methylenetetrahydrofolate reductase gene result in two enzyme isoforms". Mamm. Genome. 13 (9): 483–92. doi:10.1007/s00335-002-2167-6. PMID 12370778. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
6. Matthews RG, Daubner SC (1982). "Modulation of methylenetetrahydrofolate reductase activity by S-adenosylmethionine and by dihydrofolate and its polyglutamate analogues". Adv. Enzyme Regul. 20: 123–31. doi:10.1016/0065-2571(82)90012-7. PMID 7051769.
7. Jencks DA, Mathews RG (1987). "Allosteric inhibition of methylenetetrahydrofolate reductase by adenosylmethionine. Effects of adenosylmethionine and NADPH on the equilibrium between active and inactive forms of the enzyme and on the kinetics of approach to equilibrium". J. Biol. Chem. 262 (6): 2485–93. PMID 3818603. {{cite journal}}: Unknown parameter |month= ignored (help)
8. Yamada K, Strahler JR, Andrews PC, Matthews RG (2005). "Regulation of human methylenetetrahydrofolate reductase by phosphorylation". Proc. Natl. Acad. Sci. U.S.A. 102 (30): 10454–9. doi:10.1073/pnas.0504786102. PMC 1180802. PMID 16024724. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
9. Goyette P, Sumner JS, Milos R; et al. (1994). "Human methylenetetrahydrofolate reductase: isolation of cDNA mapping and mutation identification". Nat. Genet. 7 (4): 551. doi:10.1038/ng0894-551a. PMID 7951330. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
10. ^ Sibani S, Christensen B, O'Ferrall E, Saadi I, Hiou-Tim F, Rosenblatt DS, Rozen R (2000). "Characterization of six novel mutations in the methylenetetrahydrofolate reductase (MTHFR) gene in patients with homocystinuria". Hum. Mutat. 15 (3): 280–7. doi:10.1002/(SICI)1098-1004(200003)15:3<280::AID-HUMU9>3.0.CO;2-I. PMID 10679944.{{cite journal}}: CS1 maint: multiple names: authors list (link)
11. Schneider JA, Rees DC, Liu YT, Clegg JB (1998). "Worldwide distribution of a common methylenetetrahydrofolate reductase mutation". Am. J. Hum. Genet. 62 (5): 1258–60. doi:10.1086/301836. PMC 1377093. PMID 9545406. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
12. Frosst P, Blom HJ, Milos R, Goyette P, Sheppard CA, Matthews RG, Boers GJ, den Heijer M, Kluijtmans LA, van den Heuvel LP; et al. (1995). "A candidate genetic risk factor for vascular disease: a common mutation in methylenetetrahydrofolate reductase". Nat. Genet. 10 (1): 111–3. doi:10.1038/ng0595-111. PMID 7647779. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
13. Jacques PF, Bostom AG, Williams RR, Ellison RC, Eckfeldt JH, Rosenberg IH, Selhub J, Rozen R (1996). "Relation between folate status, a common mutation in methylenetetrahydrofolate reductase, and plasma homocysteine concentrations". Circulation. 93 (1): 7–9. PMID 8616944. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
14. ^ Yamada K, Chen Z, Rozen R, Matthews RG (2001). "Effects of common polymorphisms on the properties of recombinant human methylenetetrahydrofolate reductase". Proc. Natl. Acad. Sci. U.S.A. 98 (26): 14853–8. doi:10.1073/pnas.261469998. PMC 64948. PMID 11742092. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
15. Skibola CF, Smith MT, Kane E, Roman E, Rollinson S, Cartwright RA, Morgan G' (1999). "Polymorphisms in the methylenetetrahydrofolate reductase gene are associated with susceptibility to acute leukemia in adults". Proc. Natl. Acad. Sci. U.S.A. 96 (22): 12810–5. doi:10.1073/pnas.96.22.12810. PMC 23109. PMID 10536004. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
16. Ma J, Stampfer MJ, Giovannucci E, Artigas C, Hunter DJ, Fuchs C, Willett WC, Selhub J, Hennekens CH, Rozen R (15 March 1997). "Methylenetetrahydrofolate reductase polymorphism, dietary interactions, and risk of colorectal cancer". Cancer Res. 57 (6): 1098–102. PMID 9067278.{{cite journal}}: CS1 maint: multiple names: authors list (link)
17. "Meta-Analysis of All Published Schizophrenia-Association Studies (Case-Control Only) for rs1801133 (C677T) polymorphism, MTHFR gene". Schizophrenia Research Forum. Retrieved 2007-03-11.
18. Roffman JL, Weiss AP, Deckersbach T, Freudenreich O, Henderson DC, Purcell S, Wong DH, Halsted CH, Goff DC (2007). "Effects of the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism on executive function in schizophrenia". Schizophr. Res. 92 (1–3): 181–8. doi:10.1016/j.schres.2007.01.003. PMID 17344026. {{cite journal}}: Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
19. Stankova J, Lawrance AK, Rozen R (2008). "Methylenetetrahydrofolate reductase (MTHFR): a novel target for cancer therapy". Curr Pharm Des. 14 (11): 1143–50. doi:10.2174/138161208784246171. PMID 18473861.{{cite journal}}: CS1 maint: multiple names: authors list (link)

Further reading

Template:PBB Further reading

External links

• Smith DO (2007-02-08). "MTHFR and homocysteine". Ask Dr. Stephan Moll / Factor V Leiden / Thrombophilia Support Page. Thrombophilia Awareness Project. Retrieved 2008-08-02. {{cite web}}: Cite has empty unknown parameter: |coauthors= (help)

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• EC 1.5.1
• Human proteins