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METHOTREXATE-RESISTANT VARIANTS OF HUMAN DIHYDROFOLATE REDUCTASE WITH SUBSTITUTION OF LEUCINE 22: KINETICS, CRYSTALLOGRAPHY AND POTENTIAL AS SELECTABLE MARKERSMETHOTREXATE-RESISTANT VARIANTS OF HUMAN DIHYDROFOLATE REDUCTASE WITH SUBSTITUTION OF LEUCINE 22: KINETICS, CRYSTALLOGRAPHY AND POTENTIAL AS SELECTABLE MARKERS
Structural highlights
Disease[DYR_HUMAN] Defects in DHFR are the cause of megaloblastic anemia due to dihydrofolate reductase deficiency (DHFRD) [MIM:613839]. DHFRD is an inborn error of metabolism, characterized by megaloblastic anemia and/or pancytopenia, severe cerebral folate deficiency, and cerebral tetrahydrobiopterin deficiency. Clinical features include variable neurologic symptoms, ranging from severe developmental delay and generalized seizures in infancy, to childhood absence epilepsy with learning difficulties, to lack of symptoms.[1] [2] Function[DYR_HUMAN] Key enzyme in folate metabolism. Contributes to the de novo mitochondrial thymidylate biosynthesis pathway. Catalyzes an essential reaction for de novo glycine and purine synthesis, and for DNA precursor synthesis. Binds its own mRNA and that of DHFRL1.[3] [4] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedAlthough substitution of tyrosine, phenylalanine, tryptophan, or arginine for leucine 22 in human dihydrofolate reductase greatly slows hydride transfer, there is little loss in overall activity (kcat) at pH 7.65 (except for the arginine 22 variant), but Km for dihydrofolate and NADPH are increased significantly. The greatest effect, decreased binding of methotrexate to the enzyme-NADPH complex by 740- to 28,000-fold due to a large increase in the rate of methotrexate dissociation, makes these variants suitable to act as selectable markers. Affinities for four other inhibitors are also greatly decreased. Binding of methotrexate to apoenzyme is decreased much less (decreases as much as 120-fold), binding of tetrahydrofolate is decreased as much as 23-fold, and binding of dihydrofolate is decreased little or increased. Crystal structures of ternary complexes of three of the variants show that the mutations cause little perturbation of the protein backbone, of side chains of other active site residues, or of bound inhibitor. The largest structural deviations occur in the ternary complex of the arginine variant at residues 21-27 and in the orientation of the methotrexate. Tyrosine 22 and arginine 22 relieve short contacts to methotrexate and NADPH by occupying low probability conformations, but this is unnecessary for phenylalanine 22 in the piritrexim complex. Methotrexate-resistant variants of human dihydrofolate reductase with substitutions of leucine 22. Kinetics, crystallography, and potential as selectable markers.,Lewis WS, Cody V, Galitsky N, Luft JR, Pangborn W, Chunduru SK, Spencer HT, Appleman JR, Blakley RL J Biol Chem. 1995 Mar 10;270(10):5057-64. PMID:7890613[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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