Dihydrofolate reductase converts dihydrofolate into tetrahydrofolate, a methyl group shuttle required for the de novo synthesis of purines, thymidylic acid, and certain amino acids. While the functional dihydrofolate reductase gene has been mapped to chromosome 5, multiple intronless processed pseudogenes or dihydrofolate reductase-like genes have been identified on separate chromosomes.
DHFR catalyzes the transfer of a hydride from NADPH to dihydrofolate with an accompanying protonation to produce tetrahydrofolate. In the end, dihydrofolate is reduced to tetrahydrofolate and NADPH is oxidized to NADP+. The high flexibility of Met20 and other loops near the active site play a role in promoting the release of the product, tetrahydrofolate. In particular the Met20 loop helps stabilize the nicotinamide ring of the NADPH to promote the transfer of the hydride from NADPH to dihydrofolate.
The reduction of dihydrofolate to tetrahydrofolate.
Found in all organisms, DHFR has a critical role in regulating the amount of tetrahydrofolate in the cell. Tetrahydrofolate and its derivatives are essential for purine and thymidylate synthesis, which are important for cell proliferation and cell growth. DHFR plays a central role in the synthesis of nucleic acid precursors, and it has been shown that mutant cells that completely lack DHFR require glycine, an amino acid, and thymidine to grow. DHFR has also been demonstrated as an enzyme involved in the salvage of tetrahydrobiopterin from dihydrobiopterin 
Dihydrofolate reductase deficiency has been linked to megaloblastic anemia. Treatment is with reduced forms of folic acid. Because tetrahydrofolate, the product of this reaction, is the active form of folate in humans, inhibition of DHFR can cause functional folate deficiency. DHFR is an attractive pharmaceutical target for inhibition due to its pivotal role in DNA precursor synthesis. Trimethoprim, an antibiotic, inhibits bacterial DHFR while methotrexate, a chemotherapy agent, inhibits mammalian DHFR. However, resistance has developed against some drugs, as a result of mutational changes in DHFR itself.
Therapeutic application and disease relevance
Since folate is needed by rapidly dividing cells to make thymine, this effect may be used to therapeutic advantage.
DHFR can be targeted in the treatment of cancer. DHFR is responsible for the levels of tetrahydrofolate in a cell, and the inhibition of DHFR can limit the growth and proliferation of cells that are characteristic of cancer. Methotrexate, a competitive inhibitor of DHFR, is one such anticancer drug that inhibits DHFR. Other drugs include trimethoprim and pyrimethamine. These three are widely used as antitumor and antimicrobial agents. Whether or not these are potent anticancer agents is unclear.
Trimethoprim has shown to have activity against a variety of Gram-positive bacterial pathogens. However, resistance to trimethoprim and other drugs aimed at DHFR can arise due to a variety of mechanisms, limiting the success of their therapeutical uses. Resistance can arise from DHFR gene amplification, mutations in DHFR, decrease in the uptake of the drugs, among others. Regardless, trimethoprim and sulfamethoxazole in combination has been used as an antibacterial agent for decades.
Folic acid is necessary for growth, and the pathway of the metabolism of folic acid is a target in developing treatments for cancer. DHFR is one such target. A regimen of fluorouracil, doxorubicin, and methotrexate was shown to prolong survival in patients with advanced gastric cancer. Further studies into inhibitors of DHFR can lead to more ways to treat cancer.
Dihydrofolate reductase as a target in the treatment of anthrax
Structural alignment of dihydrofolate reductase from Bacillus anthracis (BaDHFR), Staphylococcus aureus (SaDHFR), Escherichia coli (EcDHFR), and Streptococcus pneumoniae (SpDHFR).
BaDHFR's resistance to trimethoprim analogs is due to these two residues (F96 and Y102), which also confer improved kinetics and catalytic efficiency. Current research uses active site mutants in BaDHFR to guide lead optimization for new antifolate inhibitors.
^Smith SL, Patrick P, Stone D, Phillips AW, Burchall JJ (November 1979). "Porcine liver dihydrofolate reductase. Purification, properties, and amino acid sequence". J. Biol. Chem.254 (22): 11475–84. PMID500653.
^Matthews DA, Alden RA, Bolin JT, Freer ST, Hamlin R, Xuong N, Kraut J, Poe M, Williams M, Hoogsteen K (July 1977). "Dihydrofolate reductase: x-ray structure of the binary complex with methotrexate". Science197 (4302): 452–455. doi:10.1126/science.17920. PMID17920.
^Filman DJ, Bolin JT, Matthews DA, Kraut J. (November 1982). "Crystal structure of Escherichia coli and Lactobacillus casei dihydrofolate reductase refined at 1.7 A resolution. II. Environment of bound NADPH and implications for catalysis". The Journal of Biological Chemistry257 (22): 13650–13662. PMID6815179.
^ abOsborne MJ, Schnell J, Benkovic SJ, Dyson HJ, Wright PE (August 2001). "Backbone dynamics in dihydrofolate reductase complexes: role of loop flexibility in the catalytic mechanism". Biochemistry40 (33): 9846–59. doi:10.1021/bi010621k. PMID11502178.
^Bolin JT, Filman DJ, Matthews DA, Hamlin RC, Kraut J (November 1982). "Crystal structures of Escherichia coli and Lactobacillus casei dihydrofolate reductase refined at 1.7 A resolution. I. General features and binding of methotrexate". J. Biol. Chem.257 (22): 13650–62. PMID6815178.
^Li R, Sirawaraporn R, Chitnumsub P, et al. (January 2000). "Three-dimensional structure of M. tuberculosis dihydrofolate reductase reveals opportunities for the design of novel tuberculosis drugs". J. Mol. Biol.295 (2): 307–23. doi:10.1006/jmbi.1999.3328. PMID10623528.
^Benkovic SJ, Fierke CA, Naylor AM (March 1988). "Insights into enzyme function from studies on mutants of dihydrofolate reductase". Science239 (4844): 1105–10. doi:10.1126/science.3125607. PMID3125607.
^Narayana N, Matthews DA, Howell EE, Nguyen-huu X (November 1995). "A plasmid-encoded dihydrofolate reductase from trimethoprim-resistant bacteria has a novel D2-symmetric active site". Nat. Struct. Biol.2 (11): 1018–25. doi:10.1038/nsb1195-1018. PMID7583655.
^Mayhew M, da Silva AC, Martin J, Erdjument-Bromage H, Tempst P, Hartl FU (February 1996). "Protein folding in the central cavity of the GroEL-GroES chaperonin complex". Nature379 (6564): 420–6. doi:10.1038/379420a0. PMID8559246.
Chan DC, Fu H, Forsch RA, Queener SF, Rosowsky A (June 2005). "Design, synthesis, and antifolate activity of new analogues of piritrexim and other diaminopyrimidine dihydrofolate reductase inhibitors with omega-carboxyalkoxy or omega-carboxy-1-alkynyl substitution in the side chain". J. Med. Chem.48 (13): 4420–31. doi:10.1021/jm0581718. PMID15974594.
Banerjee D, Mayer-Kuckuk P, Capiaux G, et al. (2002). "Novel aspects of resistance to drugs targeted to dihydrofolate reductase and thymidylate synthase". Biochim. Biophys. Acta1587 (2–3): 164–73. doi:10.1016/S0925-4439(02)00079-0. PMID12084458.
Stockman BJ, Nirmala NR, Wagner G, et al. (1992). "Sequence-specific 1H and 15N resonance assignments for human dihydrofolate reductase in solution". Biochemistry31 (1): 218–29. doi:10.1021/bi00116a031. PMID1731871.
Yang JK, Masters JN, Attardi G (1984). "Human dihydrofolate reductase gene organization. Extensive conservation of the G + C-rich 5' non-coding sequence and strong intron size divergence from homologous mammalian genes". J. Mol. Biol.176 (2): 169–87. doi:10.1016/0022-2836(84)90419-4. PMID6235374.
Masters JN, Yang JK, Cellini A, Attardi G (1983). "A human dihydrofolate reductase pseudogene and its relationship to the multiple forms of specific messenger RNA". J. Mol. Biol.167 (1): 23–36. doi:10.1016/S0022-2836(83)80032-1. PMID6306253.
Chen MJ, Shimada T, Moulton AD, et al. (1984). "The functional human dihydrofolate reductase gene". J. Biol. Chem.259 (6): 3933–43. PMID6323448.
Morandi C, Masters JN, Mottes M, Attardi G (1982). "Multiple forms of human dihydrofolate reductase messenger RNA. Cloning and expression in Escherichia coli of their DNA coding sequence". J. Mol. Biol.156 (3): 583–607. doi:10.1016/0022-2836(82)90268-6. PMID6750132.
Schleiff E, Shore GC, Goping IS (1997). "Human mitochondrial import receptor, Tom20p. Use of glutathione to reveal specific interactions between Tom20-glutathione S-transferase and mitochondrial precursor proteins". FEBS Lett.404 (2–3): 314–8. doi:10.1016/S0014-5793(97)00145-2. PMID9119086.
Cody V, Galitsky N, Luft JR, et al. (1997). "Comparison of two independent crystal structures of human dihydrofolate reductase ternary complexes reduced with nicotinamide adenine dinucleotide phosphate and the very tight-binding inhibitor PT523". Biochemistry36 (45): 13897–903. doi:10.1021/bi971711l. PMID9374868.
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