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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)

A method for the efficient cloning of single-copy genes from restriction digests of mammalian DNA is described. The method is illustrated by the cloning of several mutant genes as well as the wild-type gene for Chinese hamster dihydrofolate reductase (DHFR; 7,8-dihydrofolate:NADP+ oxidoreductase, EC 1.5.1.3). This gene is isolated within a 41-kilobase Bgl I fragment by using cosmid (plasmids containing a cohesive-end site) vectors that have been constructed especially for this purpose. Two cosmids are used: one contains a short region from the 5' flanking region of the dhfr gene, and the other contains a short region from the 3' flanking region. These two regions contain the Bgl I sites that bound the dhfr gene. Bgl I leaves staggered ends that are different depending on the DNA sequence within the enzyme binding site. When these cosmids are cut with Bgl I and hybridized with total Bgl I-cut genomic DNA, they preferentially associate with the fragment bearing the dhfr gene, since it has the same Bgl I ends. An approximately 500-fold enrichment for the dhfr gene in cosmid libraries from Chinese hamster ovary cells was achieved by using this method coupled with a single-step size fractionation. As a result, only several hundred cosmid colonies need to be screened in order to clone a dhfr gene from a particular mutant Chinese hamster ovary cell. This method should facilitate the repetitive cloning of any gene or gene fragment.
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PMID:Efficient cloning of single-copy genes using specialized cosmid vectors: isolation of mutant dihydrofolate reductase genes. 388 53

Dihydrofolate reductase (EC 1.5.1.3; 5,6,7,8-tetrahydrofolate:NADP(+) oxidoreductase) from antifolate-resistant Lactobacillus casei has been isolated in pure form and examined in solution by high resolution proton magnetic resonance spectroscopy. The 220 MHz proton magnetic resonance spectrum of this small enzyme (about 15,000 daltons) consists of several distinct resonance peaks that provide a sensitive nonperturbing probe of its conformational state. Comparison of catalytically active enzyme with preparations denatured in 6 M urea demonstrates dramatically the overall contribution of secondary and tertiary structure to its proton magnetic resonance spectra. More subtle differences existing among several catalytically active enzyme forms may also be readily differentiated by proton magnetic resonance spectroscopy, e.g., the spectra of the ligand-free enzyme and forms containing stoichiometric amounts of tightly bound folate and dihydrofolate, each obtained separately by affinity chromatography, are easily identified. Addition of ligands to these spectroscopically distinct forms may induce changes in their proton magnetic resonance spectra. For example, addition of equimolar dihydrofolate to the apoenzyme converts its relatively featureless aromatic proton magnetic resonance spectrum to one indistinguishable from that of the original enzyme-dihydrofolate binary complex obtained chromatographically. Interaction of the pyridine nucleotide coenzymes NADP(+) or NADPH or of the antifolate Methotrexate with apoenzyme induces additional distinct spectral changes. Enzyme-NADPH and enzyme-Methotrexate binary complexes, which have different aromatic region proton magnetic resonance spectra, are converted to ternary complexes having quite similar spectra by addition of Methotrexate and NADPH, respectively, thus suggesting that an ordered addition of ligands is not required.
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PMID:Conformational changes induced in dihydrofolate reductase by folates, pyridine nucleotide coenzymes, and methotrexate. 415 40

The amino-acid sequence of dihydrofolate reductase (7,8-dihydrofolate:NADP(+) oxidoreductase, EC 1.5.1.4) from S. faecium var Durans strain A is reported, and methionine residues 28 and 50 are shown to be protected by the inhibitor aminopterin from carboxymethylation by iodoacetate which occurs in absence of the inhibitor. Comparison of the sequence with that of the Escherichia coli reductase reveals two domains of considerable homology, one (the N-terminal region) presumably concerned with dihydrofolate and inhibitor binding and the other with dinucleotide binding. No significant sequence homology was found between larger dehydrogenases and the dihydrofolate reductases, which must, therefore, have evolved from a different ancestral protein.
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PMID:Amino-acid sequence of dihydrofolate reductase from a methotrexate-resistant mutant of Streptococcus faecium and identification of methionine residues at the inhibitor binding site. 460 2

The human dihydrofolate reductase (DHFR; tetrahydrofolate dehydrogenase; 5,6,7,8-tetrahydrofolate: NADP+ oxidoreductase, EC 1.5.1.3) gene family includes a functional gene (hDHFR) and at least four intronless genes. Three intronless genes (hDHFR-psi 2, hDHFR-psi 3, and hDHFR-psi 4) are identifiable as pseudogenes because of DNA sequence divergence from the functional gene with introns, while one intronless gene (hDHFR-psi 1) is completely homologous to the coding sequences of the functional gene. Analysis of genomic DNA from two panels of somatic human-rodent cell hybrids with specific molecular probes provide insight into the chromosomal organization and assignment of these genes. The five genes are dispersed in that each one is found on a different chromosome. The functional gene hDHFR has been assigned to chromosome 5, and one pseudogene (hDHFR-psi 4), to chromosome 3. In a human cell line (HeLa) that was selected for methotrexate resistance, the functional locus became amplified, while there was no amplification of the four intronless pseudogenes. hDHFR-psi 1 was found to be present in DNA of some individuals and absent from DNA of others, consistent with a recent evolutionary origin of this gene originally suggested by its sequence identity to the coding portions of the functional gene. The presence or absence of this intronless pseudogene represents a previously unreported form of DNA polymorphism.
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PMID:Chromosomal organization of the human dihydrofolate reductase genes: dispersion, selective amplification, and a novel form of polymorphism. 608 82

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

Dihydrofolate reductase (5,6,7,8-tetrahydrofolate: NADP+ oxidoreductase, EC 1.5.1.3) was purified from Escherichia coli strains that carried derivatives of the multicopy recombinant plasmid, pJFM8. The results of enzyme kinetic and two-dimensional gel electrophoresis experiments showed that the cloned enzyme is indistinguishable from the chromosomal enzyme. Therefore it can be concluded that these strains are ideal for use as a source of enzyme for further studies on the biochemistry and regulation of this important enzyme. The plasmid derivatives were constructed by recloning experiments that utilized several restriction endonucleases. From the analysis both of these plasmids and the purified dihydrofolate reductase enzymes it was possible to deduce the location and orientation of the dihydrofolate reductase structural gene on the parent plasmid, pJFM8.
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PMID:Characterization of the cloned Escherichia coli dihydrofolate reductase. 626 32

In the past few years we have been engaged in studying several folate cofactor requiring enzymes derived from human cells; namely thymidylate synthase, dihydrofolate reductase, folyl binder, 10-formyl-H4PteGlu synthetase, 5,10-methenyl-H4PteGlu cyclohydrolase and 5,10-methylene-H4PteGlu dehydrogenase. These have been purified and several properties have been examined, in particular the interactions with folyl-polyglutamate forms as substrates and inhibitors. Folylpolyglutamates are better substrates for thymidylate synthase, 10-formyl-H4PteGlu synthetase, and 5,10-methylene-H4PteGlu dehydrogenase when NADP is lower than 30 microM, whereas dihydrofolate reductase and membrane associated folyl binder do not distinguish between folylmono- and polyglutamates. Analog studies with thymidylate synthase suggest that there are two types of folate binding sites and this led us to propose a model for the subunit association.
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PMID:Thymidylate synthase, dihydrofolate reductase, folyl binder, 10-formyl-H4PteGlu synthetase, 5,10-methenyl-H4PteGlu cyclohydrolase and 5,10-methylene-H4PteGlu dehydrogenase derived from cells of human origin. 635 56

The alpha epimers of pyridine nucleotides are almost totally inactive as reductants in dehydrogenase reactions. In contrast, the R plasmid R67-specified dihydrofolate reductase (5,6,7,8-tetrahydrofolate: NADP+ oxidoreductase, EC 1.5.1.3) isolated from trimethoprim-resistant Escherichia coli utilized alpha-NADPH and alpha-NADH in addition to the "normal" beta-epimers. The enzymes from bacterial and mammalian sources used only beta-NADPH and beta-NADH. THe Km value for alpha-NADPH (16 microM) was 4-fold greater than that for beta-NADPH (4 microM), while the maximal velocity of the alpha-NADPH-catalyzed reaction was 70% of that seen with the beta-NADPH. beta-NADP+ and alpha-NADP+ were competitive inhibitors of the R67 enzyme. Pyridine nucleotide analogues such as deamino- and acetyl-NADPH were used readily by bacterial, plasmid, and mammalian enzymes, whereas thio-NADPH was used only by the plasmid enzyme. These data suggest that the enzyme from R plasmid R67 possesses a pyridine nucleotide binding site different from that of other dihydrofolate reductases and dehydrogenases.
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PMID:Alpha-pyridine nucleotides as substrates for a plasmid-specified dihydrofolate reductase. 641 Mar 95

The effects of ligand binding on antibody complex formation of Lactobacillus casei dihydrofolate reductase have been investigated. Binary complexes containing either substrate and inhibitors or NADP+ and NADPH together with ternary complexes containing inhibitors and coenzyme were examined. Whereas substrate and inhibitor binding alone show no effect, the binding of coenzyme reduces antibody complex formation. The most striking effect is observed with ternary complexes containing methotrexate or aminopterin and NADPH: maximal retention of the labeled protein in the immunoprecipitation assay is reduced to approximately 30% of its original value with dihydrofolate reductase alone due to a decrease in both the affinity and lifetime of the antibody-protein complex at one or more antigenic sites. This result is discussed in terms of different conformational changes brought about by NADP and NADPH.
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PMID:Immunochemical evidence for extensive ligand-induced conformational changes in Lactobacillus casei dihydrofolate reductase. 642 Mar 99

19F-n.m.r. spectroscopy was used to study the binding of 3',5'-difluoromethotrexate to dihydrofolate reductase (tetrahydrofolate dehydrogenase) from Lactobacillus casei. The benzoyl ring of the bound difluoromethotrexate was found to 'flip' about its symmetry axis, and the rate (7.3 X 10(3) s-1 at 298 K) and activation parameters for this process were determined by lineshape analysis of the 19F-n.m.r. spectrum at a series of temperatures in the range 273-308 K. The contributions to the barrier for this process are discussed. Addition of NADP+ or NADPH to form the enzyme-difluoromethotrexate-coenzyme ternary complex led to an increase in the rate of benzoyl ring flipping by a factor of 2.6-2.8-fold, and to substantial changes in the 19F-n.m.r. chemical shifts. The possible nature of the coenzyme-induced conformational changes responsible for these effects is discussed.
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PMID:19F-n.m.r. studies of 3',5'-difluoromethotrexate binding to Lactobacillus casei dihydrofolate reductase. Molecular motion and coenzyme-induced conformational changes. 642 48


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