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)

Recently the efficacy of sulfadoxine/pyrimethamine (S/P) in treatment of uncomplicated falciparum malaria in Tanzania has been seriously compromised by the development of resistance. The occurrence of active site mutations in the Plasmodium falciparum gene sequence coding for dihydrofolate reductase (DHFR) is known to confer resistance to pyrimethamine. This study investigates the occurrence of these mutations in infected blood samples taken from Tanzanian children before treatment with S/P and their relationship to parasite breakthrough by day 7. The results confirm the occurrence of one or more DHFR mutations in all the samples, but no relationship was found with the presence of parasites in the blood at day 7. The results suggest that alterations in the coding region for dihydropteroate synthetase (DHPS), the enzyme target for sulfadoxine, should be studied in order to predict resistance to the S/P combination. It has been proposed earlier that sulfadoxine could itself act on DHFR, because of a false dihydrofolate produced by drug metabolism through DHPS and dihydrofolate synthase. The results of this treatment study suggest that such a possibility is unlikely.
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PMID:High prevalence of mutations in the dihydrofolate reductase gene of Plasmodium falciparum in isolates from Tanzania without evidence of an association to clinical sulfadoxine/pyrimethamine resistance. 959 65

In the folate biosynthetic pathway, sulfa drugs (sulfonamides and sulfones) compete with the natural substrate, para-aminobenzoate (pABA) causing depletion of dihydrofolate (DHF) and subsequent growth inhibition. The sulfa drugs condense with 2-amino-4-hydroxy-6-hydroxymethyl-7,8 dihydropteridine pyrophosphate (DHPPP) forming sulfa-dihydropteroate (sulfa-DHP). Here evidence is presented using yeast that such dihydropteroate (DHP) analogs are inhibitory through competition with DHF. Two folate synthesis mutants, with respective dihydrofolate synthase (DHFS) and dihydropteroate synthase (DHPS) deletions and requiring DHF for growth were exposed to sulfa drugs. The DHFS knockout mutant was inhibited, but the DHPS knockout mutant that was incapable of forming sulfa-DHP was insensitive. Such sulfa-DHP compounds were chemically synthesized and shown to be inhibitory in vivo by competing with DHF, but in vitro assays with double the concentration of the sulfa-DHP to DHF showed no inhibition of dihydrofolate reductase (DHFR). Sequence analysis of resistant mutants obtained in the presence of sulfa drugs showed no changes in DHFR, or DHPS, unlike previously found antifolate-resistant mutants. The diamino derivatives, which are precursors of the sulfa-DHP, were found to be DHFR inhibitors. These results suggest that a new class of drugs, based on DHP analogs, could be investigated.
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PMID:Inhibition studies of sulfonamide-containing folate analogs in yeast. 1282 Jul 98

Whereas tetrahydrofolate is an essential cofactor in all bacteria, the gene that encodes the enzyme dihydrofolate reductase (DHFR) could not be identified in many of the bacteria whose genomes have been entirely sequenced. In this communication we show that the halophilic archaea Halobacterium salinarum and Haloarcula marismortui contain genes coding for proteins with an N-terminal domain homologous to dihydrofolate synthase (FolC) and a C-terminal domain homologous to dihydropteroate synthase (FolP). These genes are able to complement a Haloferax volcanii mutant that lacks DHFR. We also show that the Helicobacter pylori dihydropteroate synthase can complement an Escherichia coli mutant that lacks DHFR. Activity resides in an N-terminal segment that is homologous to the polypeptide linker that connects the dihydrofolate synthase and dihydropteroate synthase domains in the haloarchaeal enzymes. The purified recombinant H. pylori dihydropteroate synthase was found to be a flavoprotein.
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PMID:An alternative pathway for reduced folate biosynthesis in bacteria and halophilic archaea. 1555 70

We have tested the hypothesis that 2,4-diamino-6-hydroxymethyl-pteridine (DAP), 2,4-diaminopteroic acid (DAPA), and 2,4 diamino-N10-methyl-pteroic acid (DAMPA) could be converted into aminopterin (from DAP and DAPA) and methotrexate (from DAMPA), both of which are potent inhibitors of dihydrofolate reductase, a proven drug target for Plasmodium falciparum. DAP, DAPA, and DAMPA inhibited parasite growth in the micromolar range; DAMPA was the most active, with 50% inhibitory concentrations in vitro of 446 ng/ml against the antifolate-sensitive strain and 812 ng/ml against the highly resistant strain under physiological folate conditions. DAMPA potentiates the activity of the sulfone dapsone, an inhibitor of dihydropteroate synthase, but not that of chlorcycloguanil, a known inhibitor of dihydrofolate reductase (DHFR). Experiments with a Saccharomyces cerevisiae strain dependent upon the P. falciparum DHFR enzyme showed that DHFR is a target of DAMPA in that system. We hypothesize that DAMPA is converted to methotrexate by the parasite dihydrofolate synthase, which explains the synergy of DAMPA with dapsone but not with chlorcycloguanil. This de novo synthesis will not occur in the host, since it lacks the complete folate pathway. If this hypothesis holds true, the de novo synthesis of the toxic compounds could be used as a framework for the search for novel potent antimalarial antifolates.
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PMID:2,4-diaminopteridine-based compounds as precursors for de novo synthesis of antifolates: a novel class of antimalarials. 1612 35

Antimalarial chemotherapy is one of the main pillars in the prevention and control of malaria. Following widespread resistance of Plasmodium falciparum to chloroquine, sulfadoxine-pyrimethamine came to the scene as an alternative to the cheap and well-tolerated chloroquine. However, widespread resistance to sulfadoxine-pyrimethamine has been documented. In vivo efficacy tests are the gold standard for assessing drug resistance and treatment failure. However, they have many disadvantages, such as influence of host immunity and drug pharmacokinetics. In vitro tests of antimalarial drug efficacy also have many technical difficulties. Molecular markers of resistance have emerged as epidemiologic tools to investigate antimalarial drug resistance even before becoming clinically evident. Mutations in P. falciparum dihydrofolate reductase and dihydrofolate synthase have been extensively studied as molecular markers for resistance to pyrimethamine and sulfadoxine, respectively. This review highlights the resistance of P. falciparum at the molecular level presenting both supporting and opposing studies on the utility of molecular markers.
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PMID:Sulfadoxine-pyrimethamine resistance in Plasmodium falciparum: a zoomed image at the molecular level within a geographic context. 2313 24

para-Aminosalicylic acid (PAS) is one of the antimycobacterial drugs currently used for multidrug-resistant tuberculosis. Although it has been in clinical use for over 60 years, its mechanism(s) of action remains elusive. Here we report that PAS is a prodrug targeting dihydrofolate reductase (DHFR) through an unusual and novel mechanism of action. We provide evidences that PAS is incorporated into the folate pathway by dihydropteroate synthase (DHPS) and dihydrofolate synthase (DHFS) to generate a hydroxyl dihydrofolate antimetabolite, which in turn inhibits DHFR enzymatic activity. Interestingly, PAS is recognized by DHPS as efficiently as its natural substrate para-amino benzoic acid. Chemical inhibition of DHPS or mutation in DHFS prevents the formation of the antimetabolite, thereby conferring resistance to PAS. In addition, we identified a bifunctional enzyme (riboflavin biosynthesis protein (RibD)), a putative functional analog of DHFR in a knock-out strain. This finding is further supported by the identification of PAS-resistant clinical isolates encoding a RibD overexpression mutation displaying cross-resistance to genuine DHFR inhibitors. Our findings reveal that a metabolite of PAS inhibits DHFR in the folate pathway. RibD was shown to act as a functional analog of DHFR, and as for DHFS, both were shown to be associated in PAS resistance in laboratory strains and clinical isolates.
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PMID:para-Aminosalicylic acid is a prodrug targeting dihydrofolate reductase in Mycobacterium tuberculosis. 2377 5

The mechanistic basis for the resistance of Mycobacterium tuberculosis to para-aminosalicylic acid (PAS), an important agent in the treatment of multidrug-resistant tuberculosis, has yet to be fully defined. As a substrate analog of the folate precursor para-aminobenzoic acid, PAS is ultimately bioactivated to hydroxy dihydrofolate, which inhibits dihydrofolate reductase and disrupts the operation of folate-dependent metabolic pathways. As a result, the mutation of dihydrofolate synthase, an enzyme needed for the bioactivation of PAS, causes PAS resistance in M. tuberculosis strain H37Rv. Here, we demonstrate that various missense mutations within the coding sequence of the dihydropteroate (H2Pte) binding pocket of dihydrofolate synthase (FolC) confer PAS resistance in laboratory isolates of M. tuberculosis and Mycobacterium bovis. From a panel of 85 multidrug-resistant M. tuberculosis clinical isolates, 5 were found to harbor mutations in the folC gene within the H2Pte binding pocket, resulting in PAS resistance. While these alterations in the H2Pte binding pocket resulted in reduced dihydrofolate synthase activity, they also abolished the bioactivation of hydroxy dihydropteroate to hydroxy dihydrofolate. Consistent with this model for abolished bioactivation, the introduction of a wild-type copy of folC fully restored PAS susceptibility in folC mutant strains. Confirmation of this novel PAS resistance mechanism will be beneficial for the development of molecular method-based diagnostics for M. tuberculosis clinical isolates and for further defining the mode of action of this important tuberculosis drug.
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PMID:Binding pocket alterations in dihydrofolate synthase confer resistance to para-aminosalicylic acid in clinical isolates of Mycobacterium tuberculosis. 2436 31

Many microorganisms and plants possess the ability to synthesize folic acid derivatives de novo, initially forming dihydrofolate. All the folic acid derivatives that serve as recipients and donors of one-carbon units are derivatives of tetrahydrofolate, which is formed from dihydrofolate by an NADPH-dependent reduction catalyzed by dihydrofolate reductase (FolA). This review discusses the biosynthesis of dihydrofolate monoglutamate, its reduction to tetrahydrofolate monoglutamate, and the addition of glutamyl residues to form folylpolyglutamates. Escherichia coli and Salmonella, like many microorganisms that can synthesize folate de novo, appear to lack the ability to transport folate into the cell and are thus highly susceptible to inhibitors of folate biosynthesis. The review includes a brief discussion of the inhibition of folate biosynthesis by sulfa drugs. The folate biosynthetic pathway can be divided into two sections. First, the aromatic precursor chorismate is converted to paminobenzoic acid (PABA) by the action of three proteins. Second, the pteridine portion of folate is made from GTP and coupled to PABA to generate dihydropteroate, and the bifunctional protein specified by folC, dihydrofolate synthetase, or folylpolyglutamate synthetase, adds the initial glutamate molecule to form dihydrofolate (H2PteGlu1, or dihydropteroylmonoglutamate). Bacteriophage T4 infection of E. coli has been shown to cause alterations in the metabolism of folate derivatives. Infection is associated with an increase in the chain lengths in folylpolyglutamates and particularly the accumulation of hexaglutamate derivatives.
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PMID:Folate Biosynthesis, Reduction, and Polyglutamylation and the Interconversion of Folate Derivatives. 2644 88