Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0024530 (malaria)
 44,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Pyrimethamine resistance in cultivated laboratory isolates of Plasmodium falciparum is linked to the dihydrofolate reductase mutation Asn-108, a mutation that acts by interrupting drug binding within the active site of the enzyme. To determine the prevalence of this mutation in endemic regions harboring pyrimethamine-resistant malaria, we used a mutation-specific polymerase chain reaction assay to survey P. falciparum strains from a wide section of the Brazilian Amazon. Mutations were identified directly from blood samples without intervening steps of in vitro cultivation. Of 42 samples collected from four states in Brazil, 38 (90%) contained the Asn-108 codon AAC that confers pyrimethamine resistance, four samples contained only the wild-type Ser-108 codon AGC, and none contained the Thr-108 codon ACC found in cycloguanil-resistant pyrimethamine-sensitive strains. These findings indicate that a very high incidence of the Asn-108 DHFR mutation is responsible for pyrimethamine resistance in the Amazon, and they are consistent with recent failure rates reported for Fansidar (pyrimethamine-sulfadoxine). We suggest that limited use of proguanil be evaluated as an alternative to pyrimethamine.
 ...
PMID:Prevalence of the dihydrofolate reductase Asn-108 mutation as the basis for pyrimethamine-resistant falciparum malaria in the Brazilian Amazon. 195 58

Proguanil and pyrimethamine are antifolate drugs with distinct chemical structures that are used commonly in the prophylaxis and treatment of Plasmodium falciparum malaria. Clinical reports and field studies have suggested that some parasites refractory to proguanil can be treated with pyrimethamine, and vice versa. Analysis of the P. falciparum dihydrofolate reductase (DHFR) from different parasites reveals the structural basis for differential susceptibility to these antifolate drugs. Parasites harboring a pair of point mutations from Ala-16 to Val-16 and from Ser-108 to Thr-108 are resistant to cycloguanil (the active metabolite of proguanil) but not to pyrimethamine. A single Asn-108 mutation, on the other hand, confers resistance to pyrimethamine with only a moderate decrease in susceptibility to cycloguanil. Significant cross-resistance to both drugs occurs in parasites having mutations that include Ser-108----Asn-108 and Ile-164----Leu-164. These results reflect the distinct structures of pyrimethamine and cycloguanil and suggest fine differences in binding within the active site cavity of DHFR. Alternative inhibitors, used alone or in combination, may be effective against some strains of cycloguanil- or pyrimethamine-resistant malaria.
 ...
PMID:Molecular basis of differential resistance to cycloguanil and pyrimethamine in Plasmodium falciparum malaria. 218 22

The intracellular development of malaria parasites in mature erythrocytes imposes on the host cell a major demand for supply of nutrients and disposal of waste products. So as to cope with these demands, the erythrocyte membrane undergoes profound alterations in its basic permeability properties. A few hours after being invaded by Plasmodium falciparum parasites, and before any structural changes are apparent on the surface, the molecular traffic across the red cell membrane changes both in intensity and in composition of permeating substances. The changes are of a gradual nature, developmentally related and dependent on de novo protein synthesis, but do not occur concurrently for all the classes of permeants. Molecules which permeate very poorly into uninfected cells, such as hexitols (e.g., sorbitol and myoinositol), amino acids (e.g., glutamine, threonine, and histidine), a variety of organic acids and metal ions show a marked increase in their permeation rates across the host cell membrane. Likewise, substances whose normal permeation pathways conform with those of facilitated diffusion (e.g., hexoses, nucleosides, choline, and some amino acids), gain access into the host cytosol either by modified or additional permeation pathways. It has been proposed that three major new pathways are induced in the membrane of infected cells: (1) one of pore-like properties, which can accommodate most of the water soluble permeants, including anionic substances; (2) a protein-lipid interface, which can accommodate compounds of relatively higher hydrophobic character; and (3) modified constitutive transporters or modified lipid surroundings with altered transport activities. The pores are blocked by permeant bioflavonoid glycosides whose sites of binding are endofacial, and amount to less than a thousand per cell. In addition to serving as specific targets for transport blockers, the new sites of permeation can also serve as routes for enhanced delivery of cytotoxic agents into parasitized cells.
 ...
PMID:Properties of permeation pathways induced in the human red cell membrane by malaria parasites. 209 85

The falciparum interspersed repeat antigen (FIRA) plays a dominant role in the human antibody response to the malaria parasite Plasmodium falciparum. We have therefore determined the complete sequence of a genomic clone encoding FIRA. The FIRA gene contains a single intervening sequence, located immediately 3' to the putative hydrophobic core of a signal sequence in the short (100 amino acids) exon 1. The second exon largely encodes blocks of 13 hexapeptide repeats based loosely on the consensus sequence Pro-Val-Thr-Thr-Gln-Glu. The first block encoded 39 hexapeptides followed by about nine blocks of 13 hexapeptides interspersed between a conserved region of 81 amino acids, which is itself repeated along the molecule. Although deletions of repeats in this and four other independent clones make the exact number of blocks uncertain, this structure is supported by genomic blotting studies. As 31 variants of the repeat have been identified so far, we suggest that this extreme repeat variability must have important implications for the host immune response.
 ...
PMID:Structure of the FIRA gene of Plasmodium falciparum. 244 58

To investigate the genetic basis of drug resistance in human malaria parasites, we have sequenced the entire dihydrofolate reductase thymidylate synthetase DHFR-TS bifunctional gene from the highly pyrimethamine-resistant K1 isolate of Plasmodium falciparum. The protein is predicted to consist of 607 amino acids (aa), (71,685 Da), with an N-terminal methionine encoded by the second start codon of the open reading frame. Compared to the sequence from drug-sensitive parasites, there are two nucleotide changes in the coding region which bring about a substitution of Arg for Cys at aa position 59 and Asn for Thr at aa position 108. Both changes occur in regions of the DHFR domain involved in inhibitor and cofactor binding and are hence strongly implicated in drug resistance. The gene is present as a single copy in both K1 and drug-sensitive FCR3 isolates, and is assigned to chromosome 4. Codon usage follows the pattern observed in that of malarial surface antigen genes, with the exception fo codons corresponding to Val and Pro. The Asn and Lys contents of the predicted protein are exceptionally high, these residues being particularly concentrated in the DHFR and junction domains.
 ...
PMID:Characterisation of the dihydrofolate reductase-thymidylate synthetase gene from human malaria parasites highly resistant to pyrimethamine. 266 50

Antistasin, a 15-kDa salivary protein from the Mexican leech Haementeria officinalis, inhibits both blood coagulation and the metastasis of tumors (Tuszynski, G. P., Gasic, T. B., and Gasic, G. J. (1987) J. Biol. Chem. 262, 9718-9723). Antistasin binds to heparin-agarose, suggesting the protein interacts with sulfated glycoconjugates. The specificity of the interaction between antistasin and heparin was tested by measuring the binding of antistasin to various lipids and by comparing the ability of several charged glycoconjugates to inhibit binding. Of the lipids tested, antistasin binds with high affinity only to sulfatide (Gal(3-SO4)beta 1-1Cer) and does not bind to comparable levels of phospholipids, neutral glycosphingolipids, gangliosides, or cholesterol-3-SO4. The binding of antistasin to sulfatide is inhibited by dextran sulfate, fucoidan, and heparin, with I50 values of 1.5, 9.2, and 16 micrograms/ml, respectively. Comparable levels of chondroitin sulfates A, B, C, keratan sulfate, or hyaluronic acid do not inhibit binding. Comparisons of the amino acid sequences of antistasin and other sulfatide or heparin-binding proteins revealed a region of homology, based around the sequence Cys-Ser-Val-Thr-Cys-Gly-X-Gly-X-X-X-Arg-X-Arg, which may be a sulfated glycoconjugate binding domain. In addition, homologies were found with the alternate complement pathway protein properdin and coat proteins from malaria circumsporozoites and Herpes simplex I.
 ...
PMID:Antistasin, an inhibitor of coagulation and metastasis, binds to sulfatide (Gal(3-SO4) beta 1-1Cer) and has a sequence homology with other proteins that bind sulfated glycoconjugates. 274 33

Analysis of a genetic cross of Plasmodium falciparum and of independent parasite isolates from Southeast Asia, Africa, and South America indicates that resistance to pyrimethamine, an antifolate used in the treatment of malaria, results from point mutations in the gene encoding dihydrofolate reductase-thymidylate synthase (EC 1.5.1.3 and EC 2.1.1.45, respectively). Parasites having a mutation from Thr-108/Ser-108 to Asn-108 in DHFR-TS are resistant to the drug. The Asn-108 mutation occurs in a region analogous to the C alpha-helix bordering the active site cavity of bacterial, avian, and mammalian enzymes. Additional point mutations (Asn-51 to Ile-51 and Cys-59 to Arg-59) are associated with increased pyrimethamine resistance and also occur at sites expected to border the active site cavity. Analogies with known inhibitor/enzyme structures from other organisms suggest that the point mutations occur where pyrimethamine contacts the enzyme and may act by inhibiting binding of the drug.
 ...
PMID:Evidence that a point mutation in dihydrofolate reductase-thymidylate synthase confers resistance to pyrimethamine in falciparum malaria. 290 49

The effects of dietary p-aminobenzoic acid (PABA), protein, methionine and threonine on Plasmodium berghei infection in mice were investigated. Animals were fed diets containing 12 or 20% casein supplemented with PABA (0 or 2 mg/kg diet), methionine (0 or 15 mg/g casein) and threonine (0, 7.5, 27.5 or 47.5 mg/g casein). Percent mortality was lower in rats fed diets without PABA than in those fed diets containing PABA. All further experiments were conducted without supplemental PABA. While the mean day of death was greater in the groups fed 12% casein, percent mortality in these groups was nearly twofold higher than in the groups fed 20% casein. The presence or absence of 15 mg methionine per gram casein had no effect on percent mortality, mean day of death, or percent parasitemia, regardless of dietary casein level. Supplementation of threonine at any level to the 12% casein diet with supplemental methionine resulted in mortality rates similar to those from animals fed the 20% casein diets, but percent mortality was not altered by threonine in the absence of supplemental methionine. The mean day of death of animals fed 20% casein increased with increments of added threonine. Methionine had no influence on this phenomenon. It is concluded that the quantity of dietary protein and the quality of its amino acid composition can have profound effects on the susceptibility of mice to malaria.
 ...
PMID:Effects of p-aminobenzoic acid, methionine, threonine and protein levels on susceptibility of mice to Plasmodium berghei. 393 51

Infection with Plasmodium berghei malaria is severely inhibited in rats fed on a low protein diet. A range of amino acid supplements was added to a 4.2% casein diet to determine whether the relationship between level of infection and protein content could be attributed to the dietary amounts of the essential amino acids. Significant increases in levels of infection were achieved by supplementation with specific combinations of amino acids. Threonine was most effective in increasing the degree of parasitaemia but its effect was further enhanced when it was combined with dietary excess of certain other amino acids, notably valine, isoleucine and methionine.
 ...
PMID:Increased severity of malaria infection in rats fed supplementary amino acids. 639 37

The protein CD36 is a membrane receptor for thrombospondin (TSP), malaria-infected erythrocytes, and collagen. Three functional sequences were identified within a single disulfide loop of CD36: one that mediates TSP binding (amino acids 87 to 99) and two that support malarial cytoadhesion (amino acids 8 to 21 and 97 to 110). One of these peptides (p87-99) is a consensus protein kinase C (PKC) phosphorylation site. Dephosphorylation of constitutively phosphorylated CD36 in resting platelets and a megakaryocytic cell line led to the loss of collagen adhesion and platelet reactivity to collagen, with a reciprocal increase in TSP binding. PKC-mediated phosphorylation of this ectodomain resulted in a loss of TSP binding and the reciprocal acquisition of collagen binding. In site-directed mutagenesis studies, when the threonine phosphorylation site was changed to alanine, CD36 was expressed in a dephosphorylated state and bound to TSP constitutively.
 ...
PMID:Analysis of CD36 binding domains: ligand specificity controlled by dephosphorylation of an ectodomain. 750 22


1 2 3 4 5 6 7 8 9 Next >>