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

---

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

There is a need for a specific, sensitive, robust, and large-scale method for diagnosis of drug resistance genes in natural Plasmodium falciparum infections. Established polymerase chain reaction (PCR)-based methods may be compromised by the multiplicity of P. falciparum genotypes in natural infections. Here we adopt a dot-blot method to detect point mutations at nucleotide 323 (residue 108) in the P. falciparum dihydrofolate reductase (dhfr) gene using allele-specific oligonucleotide probes. Serine (Ser) or threonine (Thr) at this position are associated with sensitivity to pyrimethamine while asparagine (Asn) is associated with resistance. The method combines PCR amplification and hybridization of amplified products with radiolabeled allele-specific probes. This technique is specific and sensitive; it detects parasitemia of less than 100 parasites/microl of blood, and can identify a minority parasite genotype down to 1% in a mixture. Analysis of P. falciparum isolates from Sudan, of known response to pyrimethamine, has demonstrated the sensitivity and specificity of the method and its ability to detect multiple genotypes in single infections. Furthermore, it has confirmed the association between pyrimethamine responses and dhfr alleles. The method has been successfully extended for analysis of other point mutations in dhfr at residues 51 and 59, which are associated with a high level of pyrimethamine resistance.
...
PMID:Detection of mutations in the Plasmodium falciparum dihydrofolate reductase (dhfr) gene by dot-blot hybridization. 1236 59

The resistance to pyrimethamine (PYR) of Plasmodium falciparum arising from mutation at position 108 of dihydrofolate reductase (pfDHFR) from serine to asparagine (S108N) is due to steric interaction between the bulky side chain of N108 and Cl atom of the 5-p-Cl aryl group of PYR, which consequently resulted in the reduction in binding affinity between the enzyme and inhibitor. Molecular modeling suggested that the flexible antifolate, such as trimethoprim (TMP) derivatives, could avoid this steric constraint and should be considered as new, potentially effective compounds. The hydrophobic interaction between the side chain of inhibitor and the active site of the enzyme around position 108 was enhanced by the introduction of a longer and more hydrophobic side chain on TMP's 5-benzyl moiety. The prepared compounds, especially those bearing aromatic substituents, exhibited better binding affinities to both wild type and mutant enzymes than the parent compound. Binding affinities of these compounds correlated well with their antimalarial activities against both wild type and resistant parasites. Molecular modeling of the binding of such compounds with pfDHFR also supported the experimental data and clearly showed that aromatic substituents play an important role in enhancing binding affinity. In addition, some compounds with 6-alkyl substituents showed relatively less decrease in binding constants with the mutant enzymes and relatively good antimalarial activities against the parasites bearing the mutant enzymes.
...
PMID:Target guided synthesis of 5-benzyl-2,4-diamonopyrimidines: their antimalarial activities and binding affinities to wild type and mutant dihydrofolate reductases from Plasmodium falciparum. 1471 7

Amide and ureide biogenic enzymes were measured in the plant fraction of soybean (Glycine max) nodules during the period 11 to 23 days after inoculation with Rhizobium japonicum (USDA 3I1b142). Enzymes involved in the initial assimilation of ammonia, i.e. glutamine synthetase, glutamate synthase, and aspartate aminotransferase, showed substantial increases in their specific activities over the time course. These increases paralleled the induction of nitrogenase activity in the bacteroid and leghemoglobin synthesis in the plant fraction. The specific activity of asparagine synthetase, however, showed a rapid decline after an initial increase in specific activity. Following the initial increases in the ammonia assimilatory enzymes, there was an increase in the activity of 5-phosphoribosylpyrophosphate amidotransferase, the enzyme which catalyzes the first committed step of de novo purine biosynthesis. This was followed by a dramatic increase in the purine oxidative enzymes, xanthine dehydrogenase and uricase. Smaller increases were observed in the activities of enzymes associated with the supply of metabolites to the purine biosynthetic pathway: phosphoglycerate dehydrogenase, serine hydroxymethylase, and methylene tetrahydrofolate dehydrogenase.The concentration of asparagine in the plant fraction decreased at the same time as the observed decrease in asparagine synthetase activity. This was followed by a recovery in plant fraction levels of asparagine in the presence of a continuing fall in the glutamine concentration and continued low asparagine synthetase activity.The data presented are consistent with initial assimilation of ammonia into glutamine and aspartate, which are metabolized by an elevation of endogenous purine biosynthetic enzymes, and then, by the induction of a specific group of purine oxidative enzymes, directed to allantoic acid production.
...
PMID:Enzymes of amide and ureide biogenesis in developing soybean nodules. 1666 97

Pyrimethamine analogs were examined as potential agents against vivax malaria using a bacterial surrogate system carrying Plasmodium vivax dihydrofolate reductase-thymidylate synthase (PvDHFR-TS), in which the PvDHFR complemented chemically knocked out host dihydrofolate reductase. The system was initially tested with P. falciparum dihydrofolate reductase-thymidylate synthase and was found to have good correlation with the parasite-based system. The 50% inhibitory concentrations derived from PvDHFR-TS-dependent bacteria were correlated with their corresponding inhibition constants (Ki) from an enzyme inhibition assay, pointing to the likelihood that the potent enzyme inhibitors will also have potent antimalarial activities. Active compounds against both wild-type and S58R S117N (SP21) double-mutant P. vivax include analogs with structures which can avert a steric clash with the asparagine (S117N) side chain of the mutant, similar to those found for homologous Plasmodium falciparum mutants, raising the possibility that the same compounds can be developed against both types of antifolate-resistant malaria. This rapid and convenient drug screening system should be useful for development of new antifolates against P. vivax, for which a continuous culture system is not yet available.
...
PMID:Evaluation of the activities of pyrimethamine analogs against Plasmodium vivax and Plasmodium falciparum dihydrofolate reductase-thymidylate synthase using in vitro enzyme inhibition and bacterial complementation assays. 1695 16

One in four proteins in Plasmodium falciparum contains asparagine repeats. We probed the function of one such 28-residue asparagine repeat present in the P. falciparum proteasome lid subunit 6, Rpn6. To aid our efforts, we developed a regulatable, fluorescent affinity (RFA) tag that allows cellular localization, manipulation of cellular levels, and affinity isolation of a chosen protein in P. falciparum. The tag comprises a degradation domain derived from Escherichia coli dihydrofolate reductase together with GFP. The expression of RFA-tagged proteins is regulated by the simple folate analog trimethoprim (TMP). Parasite lines were generated in which full-length Rpn6 and an asparagine repeat-deletion mutant of Rpn6 were fused to the RFA tag. The knockdown of Rpn6 upon removal of TMP revealed that this protein is essential for ubiquitinated protein degradation and for parasite survival, but the asparagine repeat is dispensable for protein expression, stability, and function. The data point to a genomic mechanism for repeat perpetuation rather than a positive cellular role. The RFA tag should facilitate study of the role of essential genes in parasite biology.
...
PMID:Asparagine repeat function in a Plasmodium falciparum protein assessed via a regulatable fluorescent affinity tag. 2136 62

Queuosine is a modified pyrrolopyrimidine nucleoside found in the anticodon loop of transfer RNA acceptors for the amino acids tyrosine, asparagine, aspartic acid, and histidine. Because it is exclusively synthesized by bacteria, higher eukaryotes must salvage queuosine or its nucleobase queuine from food and the gut microflora. Previously, animals made deficient in queuine died within 18 days of withdrawing tyrosine, a nonessential amino acid, from the diet (Marks, T., and Farkas, W. R. (1997) Biochem. Biophys. Res. Commun. 230, 233-237). Here, we show that human HepG2 cells deficient in queuine and mice made deficient in queuosine-modified transfer RNA, by disruption of the tRNA guanine transglycosylase enzyme, are compromised in their ability to produce tyrosine from phenylalanine. This has similarities to the disease phenylketonuria, which arises from mutation in the enzyme phenylalanine hydroxylase or from a decrease in the supply of its cofactor tetrahydrobiopterin (BH4). Immunoblot and kinetic analysis of liver from tRNA guanine transglycosylase-deficient animals indicates normal expression and activity of phenylalanine hydroxylase. By contrast, BH4 levels are significantly decreased in the plasma, and both plasma and urine show a clear elevation in dihydrobiopterin, an oxidation product of BH4, despite normal activity of the salvage enzyme dihydrofolate reductase. Our data suggest that queuosine modification limits BH4 oxidation in vivo and thereby potentially impacts on numerous physiological processes in eukaryotes.
...
PMID:Queuosine deficiency in eukaryotes compromises tyrosine production through increased tetrahydrobiopterin oxidation. 2148 17

Given that the evolution and spread of resistance to sulfadoxine-pyrimethamine (SP) have been documented at a quick pace worldwide, the present study investigated the mutant Plasmodium falciparum dihydrofolate reductase 108-asparagine (dhfr 108 N) as a key marker of resistance to the combination among parasite isolates from Hodeidah. The association of parasitologic indices with the dhfr 108 N mutant allele was also studied. Ninety patients with microscopically confirmed P. falciparum infection from Hodeidah were included in the present study. Polymerase chain reaction-restriction fragment length polymorphism approach was adopted for the molecular detection of this marker. The dhfr 108 N was detected among about 61% of P. falciparum isolates, in its pure and mixed-type forms, from Hodeidah. Age, gender and residence of patients were not significant predictors for the presence of the mutant allele among parasite isolates. In contrast, a history of malaria and antimalarial drug intake in the year preceding the study as well as frequent antimalarial drug intake were significantly associated with this mutant allele. The high frequency of dhfr 108 N among parasites isolates makes the role of SP questionable as a partner with outstanding effectiveness within the ACT, at least, in the near future. SP plus artesunate should be monitored for its antimalarial efficacy at regular intervals, preferably through the molecular detection of resistance-associated mutations.
...
PMID:Prevailing Plasmodium falciparum dihydrofolate reductase 108-asparagine in Hodeidah, Yemen: a questionable sulfadoxine-pyrimethamine partner within the artemisinin-based combination therapy. 2440 51


<< Previous 1 2 3

---