Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.5.1.3 (dihydrofolate reductase)
5,819 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Oligonucleotide-directed, site-specific mutagenesis was used to convert phenylalanine-31 of human recombinant dihydrofolate reductase (DHFR) to leucine. This substitution was of interest in view of earlier chemical modification studies (Kumar et al., 1981) and structural studies based on X-ray crystallographic data (Matthews et al., 1985a,b) which had implicated the corresponding residue in chicken liver DHFR, Tyr-31, in the binding of dihydrofolate. Furthermore, this particular substitution allowed testing of the significance of protein sequence differences between mammalian and bacterial reductases at this position with regard to the species selectivity of trimethoprim. Both wild-type (WT) and mutant (F31L) enzymes were expressed and purified by using a heterologous expression system previously described (Prendergast et al., 1988). Values of the inhibition constants (Ki values) for trimethoprim were 1.00 and 1.08 microM for WT and F31L, respectively. Thus, the presence of phenylalanine at position 31 in human dihydrofolate reductase does not contribute to the species selectivity of trimethoprim. The Km values for nicotinamide adenine dinucleotide phosphate (reduced) (NADPH) and dihydrofolate were elevated 10.8-fold and 9.4-fold, respectively, for the mutant enzyme, whereas the Vmax increased only 1.8-fold. Equilibrium dissociation constants (KD values) were obtained for the binding of NADPH and dihydrofolate in binary complexes with each enzyme. The KD for NADPH is similar in both WT and F31L, whereas the KD for dihydrofolate is 43-fold lower in F31L. Values for dihydrofolate association rate constants (kon) with enzyme and enzyme-NADPH complexes were measured by stopped-flow techniques.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of conversion of phenylalanine-31 to leucine on the function of human dihydrofolate reductase. 276 6

In a semi-defined minimal medium for cultivation of Plasmodium falciparum, ribose, mannose, fructose, galactose, and maltose could not replace glucose. Hypoxanthine was the preferred purine source for the parasite over adenine, guanine, inosine, adenosine and guanosine although all supported growth equally. Inhibitors of nucleoside uptake had low potency in killing the parasites but depressed incorporation of [3H]adenosine more than [3H]hypoxanthine. Glutamate could not be replaced by 5-oxoproline, indicating that the gamma-glutamyl transferase pathway for amino acid uptake is probably not found in this organism. Adenine, nicotinamide, and orotic acid could not supplement glutamine-deficient medium. The pyridoxine antagonists isoniazid and 4-deoxypyridoxine were reversed by amino acid supplementation, suggesting that transaminases may be targets of these drugs. Orotic acid, but not glutathione or its amino acid components, partially reversed the effects of 8-methylamino-8-desmethyl riboflavin. Thus, the flavin enzyme, dihydroorotic acid dehydrogenase, but not glutathione reductase, appears to be a target of this riboflavin antagonist. Five biotin antagonists had no significant activity. The choline antagonist 2-(tert-butylamino)ethanol and thiamin uptake inhibitors had nonspecific inhibitory effects, which were not reversed by the respective target vitamin. Buthionine sulfoximine and methionine sulfoximine, inhibitors of glutathione synthesis, had significant oxygen-dependent toxicity. Six sulfonamides showed marked variation in potency and efficacy. Sulfathiazole and sulfadoxine were reversed differentially by p-aminobenzoic acid, folic acid, and folinic acid. Folinic acid was more effective than folic acid at reversing the toxicity of the dihydrofolate reductase inhibitors aminopterin and pyrimethamine; p-amino-benzoic acid had no effect.
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PMID:Nutritional requirements of Plasmodium falciparum in culture. III. Further observations on essential nutrients and antimetabolites. 286 44

A procaryotic high-level expression vector for human dihydrofolate reductase has been constructed and the protein characterized as a first step toward structure-function studies of this enzyme. A vector bearing the tac promoter, four synthetic oligodeoxynucleotides, and a restriction fragment from the dihydrofolate reductase cDNA were ligated in a manner which optimized the transcriptional and translational frequency of the enzyme mRNA. The reductase, comprising ca. 17% of the total soluble protein in the host bacteria, was purified to apparent homogeneity as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and characterized by amino acid composition, partial amino acid sequence, and steady-state kinetic analysis. This expression vector has been used as a template for double-stranded plasmid DNA site-specific mutagenesis. Functional studies on a Cys-6----Ser-6 mutant enzyme support the contention that Cys-6 is obligatory for organomercurial activation of human dihydrofolate reductase. The Ser-6 mutant enzyme was not activated to any extent following a 24-h incubation with p-(hydroxymercuri)benzoate and nicotinamide adenine dinucleotide phosphate (reduced) (NADPH), whereas the kcat for Cys-6 reductase increased 2-fold under identical conditions. The specific activities of the Cys-6 and Ser-6 enzymes were virtually identical as determined by methotrexate titration as were the Km values for both dihydrofolate and NADPH. The Ser-6 mutant showed a decreased temperature stability and was more sensitive to inactivation by alpha-chymotrypsin when compared to the wild-type enzyme. These results suggest that the Ser-6 mutant reductase is conformationally altered relative to the Cys-6 native enzyme.
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PMID:Expression and site-directed mutagenesis of human dihydrofolate reductase. 304 47

Peptides from human dihydrofolate reductase (DHFR) generated by cyanogen bromide cleavage and corresponding to residues 15-52, 53-111, 112-125, and 140-186 (carboxyl terminus) were purified and used to immunize rats. Titration of the immune sera against denatured human DHFR by solid-phase immunoassay showed that peptides 15-52 and 140-186 were relatively highly immunogenic, unlike the native enzyme which is most immunogenic in the sequence 53-111. The antisera were specific for the corresponding peptides used for immunization. Antibodies to peptides 15-52, 53-111, and 140-186 cross-reacted with native human DHFR in solution in competition assays. However, the binding of nicotinamide adenine dinucleotide phosphate (reduced) (NADPH) and the inhibitors folate and methotrexate, both in binary and in ternary complexes with the enzyme, caused a striking reduction in binding of antibody. Using a sensitive radioactive assay, it was found that antisera to peptides 15-52 and 140-186, both of which exhibited a high antibody titer, caused significant inhibition of DHFR. Because peptide 140-186 does not include any active-site residues, it is concluded that at least in this case all the antibodies bound to regions outside the active site. Since comparison of the X-ray structures of the chicken liver DHFR holoenzyme with the apoenzyme reveals no changes in secondary structural elements (alpha-helices and beta-sheets), the reduction in antibody binding to DHFR-ligand complexes must not involve epitopes within these structures.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Ligand-induced structural constraints in human dihydrofolate reductase revealed by peptide-specific antibodies. 304 92

Refined crystal structures are reported for complexes of Escherichia coli and chicken dihydrofolate reductase containing the antibiotic trimethoprim (TMP). Structural comparison of these two complexes reveals major geometrical differences in TMP binding that may be important in understanding the stereo-chemical basis of this inhibitor's selectivity for bacterial dihydrofolate reductases. For TMP bound to chicken dihydrofolate reductase we observe an altered binding geometry in which the 2,4-diaminopyrimidine occupies a position in closer proximity (by approximately 1 A) to helix alpha B compared to the pyrimidine position for TMP or methotrexate bound to E. coli dihydrofolate reductase. One important consequence of this deeper insertion of the pyrimidine into the active site of chicken dihydrofolate reductase is the loss of a potential hydrogen bond that would otherwise form between the carbonyl oxygen of Val-115 and the inhibitor's 4-amino group. In addition, for TMP bound to E. coli dihydrofolate reductase, the inhibitor's benzyl side chain is positioned low in the active-site pocket pointing down toward the nicotinamide-binding site, whereas, in chicken dihydrofolate reductase, the benzyl group is accommodated in a side channel running upward and away from the cofactor. As a result, the torsion angles about the C5-C7 and C7-C1' bonds for TMP bound to the bacterial reductase (177 degrees, 76 degrees) differ significantly from the corresponding angles for TMP bound to chicken dihydrofolate reductase (-85 degrees, 102 degrees). Finally, when TMP binds to the chicken holoenzyme, the Tyr-31 side chain undergoes a large conformational change (average movement is 5.4 A for all atoms beyond C beta), rotating down into a new position where it hydrogen bonds via an intervening water molecule to the backbone carbonyl oxygen of Trp-24.
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PMID:Refined crystal structures of Escherichia coli and chicken liver dihydrofolate reductase containing bound trimethoprim. 388 Jul 42

Three methotrexate (MTX)-resistant cell lines and their MTX-sensitive counterparts have been used to examine 2,4-diamino-6-(2,5-dimethoxybenzyl)-5-methyl-pyrido[2,3-d]pyrimidine (BW301U), a novel lipophilic antifolate, and compare its cytotoxicity with MTX and metoprine. Collateral sensitivity for both BW301U and metoprine was observed in CCRF-CEM/MTX R-cells, where MTX resistance appeared to be primarily due to a deficiency in drug uptake. This was particularly pronounced with BW301U which proved to be as effective in killing CCRF-CEM/MTX R as was MTX with the parental CCRF-CEM cell line. This effect was not seen in other cell lines, L5178Y/MTX or L1210/MTX R, where resistance to MTX was correlated with either an overproduction of 5,6,7,8-tetrahydrofolate:nicotinamide adenine dinucleotide phosphate oxidoreductase EC 1.5.1.3 (DHFR) or with combined uptake defect and increased DHFR levels, respectively. In each case, however, BW301U and metoprine, especially at high concentrations, were more effective than MTX in treating MTX-resistant cells.
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PMID:Selective toxicity of a new lipophilic antifolate, BW301U, for methotrexate-resistant cells with reduced drug uptake. 397 88

Various properties of the bacteriophage structural dihydrofolate reductase (DFR) have been examined to determine its function during phage infection. It has been found that a binding site for reduced nicotinamide adenine dinucleotide phosphate (NADPH), most likely on the DFR present in the phage tail plate, is required for phage viability. Attachment of adenosine diphosphoribose, an analogue of NADPH, to this site prevents phage adsorption and injection. This adenosine diphosphoribose inhibition can be competitively reversed by the addition of NADPH or oxidized nicotinamide adenine dinucleotide phosphate. It is suggested that, during phage infection, the host bacterial cell might leak compounds functionally similar to the pyridine nucleotides. These compounds have been shown to nonenzymatically change the conformation of the phage tail plate DFR which is apparently necessary for successful injection.
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PMID:Function of T4D structural dihydrofolate reductase in bacteriophage infection. 414 94

Transferred nuclear Overhauser effect measurements have been made on complexes of NADP+ and thioNADP+ with Lactobacillus casei dihydrofolate reductase to provide information about the glycosidic bond conformations in these complexes. Both NADP+ and thioNADP+ are shown to have very similar anti conformations about their adenine glycosidic bonds when bound to the enzyme. However, their nicotinamide glycosidic bond conformations are very different: while NADP+ binds in an exclusively anti conformation, thioNADP+ binds with a distribution of syn/anti conformations very similar to that observed in nicotinamide mononucleotides in free solution (approximately 50:50). Thus for thioNADP+, binding to the enzyme does not significantly perturb the potential function for rotation about the nicotinamide glycosidic bond. Earlier NMR studies [Hyde, E. I., Birdsall, B., Roberts, G. C. K., Feeney, J., & Burgen, A. S. V. (1980) Biochemistry 19, 3738] had indicated that large downfield 1H shifts of the nicotinamide ring protons (0.61-1.36 ppm) are detected on binding NADP+ while only very small shifts (less than 0.1 ppm) are observed in complexes with thioNADP+. The chemical shift and conformational findings are best explained if the thionicotinamide ring extends into solution making essentially no contacts with the enzyme.
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PMID:Use of transferred nuclear Overhauser effect measurements to compare binding of coenzyme analogues to dihydrofolate reductase. 622 Jul 34

The complex of Lactobacillus casei dihydrofolate reductase with trimethoprim and NADP+ exists in solution as a mixture of approximately equal amounts of two slowly interconverting conformational states [Gronenborn, A., Birdsall, B., Hyde, E. I., Roberts, G. C. K., Feeney, J., & Burgen, A. S. V. (1981) Mol. Pharmacol. 20, 145]. These have now been further characterized by multinuclear NMR experiments, and a partial structural model has been proposed. 1H NMR spectra at 500 MHz show that the environments of six of the seven histidine residues differ between the two conformations. The characteristic 1H and 31P chemical shifts of nuclei of the coenzyme in the two conformations of the complex are identical in analogous complexes formed with a number of trimethoprim analogues, indicating that the nature of the two conformations is the same in each case. The pyrophosphate 31P resonances have been assigned to the two conformations, and integration of the 31P spectrum shows that the ratio of conformation I to conformation II varies from 0.4 to 2.3 in the complexes with the various trimethoprim analogues, the ratio for the trimethoprim complex itself being 1.2. Transferred NOE experiments, together with the 1H and 13C chemical shifts, indicate that in conformation II of the complex the nicotinamide ring of the coenzyme has swung away from the enzyme surface into solution; this is made possible by changes in the conformation of the pyrophosphate moiety. In conformation I, by contrast, the nicotinamide ring remains bound to the enzyme. 13C and 15N experiments show that trimethoprim is protonated on N1 in both conformations of the ternary complex. Analysis of the 1H chemical shifts of trimethoprim in terms of ring current effects shows that in conformation I of the ternary complex trimethoprim retains the same conformation as in its binary complex, but 13C, 15N, and 19F [using 2,4-diamino-5-(3,5-dimethoxy-4-fluoro-benzyl)pyrimidine] experiments show that the environment of both the pyrimidine ring and benzyl ring is affected by the proximity of the coenzyme. Less information is available about the conformation of the inhibitor in conformation II of the complex, but its environment is similar to that in the binary enzyme-inhibitor complex. The implications of the existence of these two conformations of the enzyme for understanding cooperativity in binding between NADP+ and trimethoprim are briefly discussed.
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PMID:Multinuclear NMR characterization of two coexisting conformational states of the Lactobacillus casei dihydrofolate reductase-trimethoprim-NADP+ complex. 643 42

5-Formyltetrahydrofolate promotes the net dissociation of methotrexate bound to dihydrofolate reductase in the Ehrlich ascites tumor (L. H. Matherly et al., Cancer Res., 43: 2694-2699, 1983). Treatment of Ehrlich tumor cells with glucose or inhibitors of electron transfer stabilized the association of the antifolate with dihydrofolate reductase as reflected by a 2-fold increased fraction of dihydrofolate reductase-bound methotrexate and an abolition of the 5-formyltetrahydrofolate-induced dissociation of the inhibitor-enzyme complex. Glucose and azide were also found to increase the intracellular ratio of reduced nicotinamide adenine dinucleotide phosphate (NADPH) to oxidized nicotinamide adenine dinucleotide phosphate (NADP+) in the tumor approximately 8- and 11-fold, respectively. However, other agents which enhanced the association between methotrexate and its target enzyme were less effective in increasing the intracellular level of NADPH relative to NADP+. Micromolar concentrations of NADPH promoted methotrexate binding to the purified Ehrlich tumor dihydrofolate reductase. Bound methotrexate could be dissociated from the purified enzyme by 5-methyltetrahydrofolate but less readily by 5-formyltetrahydrofolate and only in the presence of reduced levels of NADPH relative to NADP+. The tetraglutamate derivative of 5-methyltetrahydrofolate was even more effective than the underivatized compound in dissociating methotrexate from dihydrofolate reductase. These findings suggest a critical role for the cellular oxidation-reduction state in determining the affinity of dihydrofolate reductase for methotrexate and thus the cellular sensitivity to the antifolate. In addition, the data are consistent with the possibility that dihydrofolate reductase is a key locus for intracellular competitive interactions between reduced folates and methotrexate during leucovorin rescue from the pharmacological effects of the antifolate.
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PMID:Role of the cellular oxidation-reduction state in methotrexate binding to dihydrofolate reductase and dissociation induced by reduced folates. 660 65


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