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

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.
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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.
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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.
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PMID:Evidence that a point mutation in dihydrofolate reductase-thymidylate synthase confers resistance to pyrimethamine in falciparum malaria. 290 49

We have statistically analysed the distribution of nucleotides and dinucleotides in 21 genes of the 81% A + T-rich human malaria parasite Plasmodium falciparum. The mRNA-synonymous strands of this protozoan show in general a marked excess of purines over pyrimidines, correlated with abnormally high levels of Lys and Glu. We have used the large differences in base composition between coding and non-coding regions to estimate that the parasite possesses in the range of 2700-5400 genes. The dinucleotide preference patterns are compared with consensus patterns derived from other organisms [Nussinov, Nucl. Acids Res. 12 (1984) 1749-1763]. Patterns in the coding regions surprisingly resemble those of higher, rather than lower eukaryotes, particularly with respect to TG elevation and CG suppression. The latter is correlated with an abnormally low level of Arg in these parasites. In the non-coding regions, the four dinucleotides made up of C and/or G are found with significantly higher frequencies than expected (approx. 50-150%), specifically to the 5' side of the coding regions. The possible role of these dinucleotides in control sequences is discussed.
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PMID:Anomalous dinucleotide frequencies in both coding and non-coding regions from the genome of the human malaria parasite Plasmodium falciparum. 332 56

The immunodominant repeat region of the malaria circumsporozoite protein from Plasmodium falciparum was purified from a recombinant Escherichia coli to study as a potential subunit vaccine. The recombinant protein, R32Leu-Arg, is composed of 32 tetrapeptide repeat sequences from the circumsporozoite protein (R32) linked to the dipeptide, Leu-Arg. R32Leu-Arg was purified by a series of precipitation steps including temperature, ammonium sulfate, and acid pH treatments; followed by reversed-phase high-performance liquid chromatography (RP-HPLC). An automated RP-HPLC assay was developed to measure the R32Leu-Arg concentration during both fermentation and purification. This assay was used in a variety of applications including measurement of production levels of the antigen during fermentation, evaluation of the protein purification process, quantitation of protein recovery, and as one criterion of protein purity. With minimal changes, the assay conditions were easily adapted to the semi-preparative level to produce 200 mg of purified product. The purified product was characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis; amino acid composition; and analytical size-exclusion and RP-HPLC.
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PMID:Assay, purification and characterization of a recombinant malaria circumsporozoite fusion protein by high-performance liquid chromatography. 332 67

Fluorescence histochemical methods for the demonstration of specific residues in peptides and proteins are reviewed: Formaldehyde-ozone for NH2-terminal tryptophan, formaldehyde-HCl for tryptophan regardless of position in the peptide, OPT for NH2-terminal histidine, formaldehyde-fluorescamine for "protected" amino groups, nitroso-naphthol for tyrosine, and phenanthrenequinone for arginine residues. The methods are potent in demonstrating granule-stored material in peptide hormone-producing cells. Also quinacrine, the fluorescent anti-malaria agent, binds to granular components, as yet unidentified, in several endocrine cell types. In many cases the fluorescence histochemical methods seem to demonstrate peptides and proteins distinct from the known hormones.
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PMID:Fluorescence histochemical methods for the study of peptide hormone-producing cells. 629 61

Plasmodium berghei-infected mouse red cells have enhanced fusion capacity as triggered by addition of poly(ethylene glycol) in the presence of Ca2+. The uptake of Ca2+ in P. berghei-infected cells is greater than in normal cells, and the difference in Ca2+ uptake was found to be enhanced in the presence of poly(ethylene glycol). Fusion of normal and P. berghei-infected red cells by poly(ethylene glycol) was significantly inhibited by N-tosyl-L-lysylchloromethyl ketone and phenylmethylsulphonyl fluoride. In addition, ethyleneglycolbis(aminoethylether)tetra-acetate, N-ethylmaleimide, iodoacetamide, cystamine and tetrathionate also prevented fusion in both systems. In contrast, N-tosyl-L-phenylalanylchloromethyl ketone and N-tosyl-L-arginine methyl ester did not inhibit cell fusion. The latter enhanced fusion of infected cells but was without effect on normal cells. These results indicate that a Ca2+-activated thiol proteinase may be involved in membrane fusion in malaria-infected as well as in normal red cells. However, differences in the effect of proteinase inhibitors and substrate on fusion and Ca2+ entry show that the processes leading to fusion may not be identical.
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PMID:Mechanism of enhanced fusion capacity of mouse red cells infected with Plasmodium berghei. 641 72

Examination of the proliferative responses in vitro to mitogens (concanavalin A, phytohemagglutinin, lipopolysaccharide) of spleen cells recovered from C57BL/6 mice during blood-stage Plasmodium chabaudi AS infection revealed that the most severe suppression occurred during the first 14 days post infection, that is, during the acute phase of infection. Coincidently, inducible nitric oxide synthase gene expression was found to be up-regulated in the spleens of infected mice, and both splenic and peritoneal macrophages produced high levels of NO in vitro in response to stimulation with lipopolysaccharide (LPS). The roles of NO, a molecule recently found to mediate immunosuppression during parasitic infections, and of the well-recognized immunosuppressive molecule prostaglandin were, therefore, investigated in the suppression of proliferation to mitogens and specific antigen of spleen cells from 7- and 14-day P. chabaudi AS-infected mice. Addition of either 0.5 mM NG-monomethyl-L-arginine (L-NMMA) or 0.5 mM aminoguanidine (AG), inhibitors of NO synthase, or 10 micrograms/ml indomethacin (INDO), a prostaglandin inhibitor, partially but significantly abrogated the suppression in response to concanavalin A (Con A) and phytohemagglutinin (PHA). Only the addition of INDO significantly increased the responses to LPS. Addition of L-NMMA or AG in combination with INDO partially but significantly abrogated the suppression in response to Con A and completely abrogated the suppression in response to PHA. The addition of L-NMMA or AG also significantly increased proliferation in response to parasite antigen. The contribution of NO to suppression of lymphoproliferation was confirmed by adding 3-morpholino-sydnonimine-hydrochloride (SIN-1), a chemical generator of NO, to mitogen-stimulated splenocyte cultures prepared from normal mice. The mechanism of NO-mediated suppression was investigated in coculture experiments using spleen cells from normal mice and peritoneal macrophages from either normal or day 7 infected mice. The addition of 5-10 x 10(4) peritoneal macrophages from infected mice significantly and consistently suppressed Con A- or PHA-stimulated proliferation of normal splenocytes. Moreover, suppression correlated with production of NO and could be reversed by the addition of L-NMMA or AG. These results suggest that, in addition to prostaglandin, increased NO production by macrophages within the first 2 weeks after infection with P. chabaudi AS contributes to immunosuppression associated with blood-stage malaria.
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PMID:Role of macrophage-derived nitric oxide in suppression of lymphocyte proliferation during blood-stage malaria. 754 5

Nitric oxide (NO), a highly diffusible cellular mediator involved in a wide range of biological effects, has been indicated as one of the cytotoxic agents released by leukocytes to counteract malaria infection. On the other hand, NO has been implicated as a mediator of the neuropathological symptoms of cerebral malaria. In such circumstances NO production has been thought to be induced in host tissues by host-derived cytokines. Here we provide evidence for the first time that human red blood cells infected by Plasmodium falciparum (IRBC) synthesize NO. The synthesis of NO (measured as citrulline and nitrate production) appeared to be very high in comparison with human endothelial cells; no citrulline and nitrate production was detectable in noninfected red blood cells. The NO synthase (NOS) activity was very high in the lysate of IRBC (while not measurable in that of normal red blood cells) and was inhibited in a dose-dependent way by three different NOS inhibitors (L-canavanine, NG-amino-L-arginine, and NG-nitro-L-arginine). NOS activity in P. falciparum IRBC is Ca++ independent, and the enzyme shows an apparent molecular mass < 100 kD, suggesting that the parasite expresses an isoform different from those found in mammalian cells. IRBC release a soluble factor able to induce NOS in human endothelial cells. Such NOS-inducing activity is not tissue specific, is time and dose dependent, requires de novo protein synthesis, and is probably associated with a thermolabile protein having a molecular mass > 100 kD. Our data suggest that an increased NO synthesis in P. falciparum malaria can be directly elicited by soluble factor(s) by the blood stages of the parasite, without necessarily requiring the intervention of host cytokines.
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PMID:Erythrocyte stages of Plasmodium falciparum exhibit a high nitric oxide synthase (NOS) activity and release an NOS-inducing soluble factor. 754 94

Intraperitoneal injection of recombinant Interleukin 12 (rIL-12) at 30 ng/day for 5 days beginning 1 to 2 days before sporozoite challenge or administration of a single dose of 150 ng of rIL-122 days before challenge protected 100% of BALB/c mice against challenge with 10(2) Plasmodium yoelii sporozoites. rIL-12-induced protection was eliminated in all mice by administration of a monoclonal antibody against interferon gamma and in 50% of mice by administration of NG-monomethyl-L-arginine, a competitive inhibitor of nitric oxide synthase. rIL-12 protected BALB/c mice treated with cytotoxic anti-CD4 and anti-CD8 monoclonal antibodies, as well as T-cell- and B-cell-deficient severe combined immunodeficiency mice. These data suggest that rIL-12 stimulates non-B, non-T cells to produce interferon gamma that kills intrahepatic parasites by stimulating nitric oxide production. If rIL-12 proves to be well tolerated by humans, our findings support consideration of rIL-12 as an immunoprophylactic against malaria.
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PMID:Interleukin 12 induction of interferon gamma-dependent protection against malaria. 793 13


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