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)

A method for purification of a recombinant Plasmodium falciparum protein produced in E. coli and its use in an enzyme-linked immunosorbent assay (ELISA) is described. The cloned gene fragment encodes GLURP,489-1271 the carboxy-terminal 783 amino acid residue portion of a 1271 amino acid residue P. falciparum glutamate rich protein (GLURP), with a molecular weight of 220 kilodalton. The protein is associated with all parasite stages in the human host. Examination of sera from 105 adult Liberians living in a malaria endemic area revealed anti-GLURP IgG antibodies in 98% of the sera. The recombinant GLURP489-1271 was expressed as a chimeric protein, fused with E. coli beta-galactosidase. However, antibodies in sera were directed only against the malaria part of the fusion protein and not against beta-galactosidase. Antigen from in vitro P. falciparum cultures of isolates from Tanzania (F32), Papua New Guinea (MAD20) and Honduras (HB3) completely absorbed specific antibodies, indicating the presence of conserved epitopes produced by all isolates of P. falciparum. Recombinant GLURP489-1271 ELISA is sensitive and rapid, and therefore well-suited for sero-epidemiological studies, and for control of the immunogenicity of a possible future P. falciparum vaccine utilizing epitopes from GLURP.
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PMID:Recombinant Plasmodium falciparum glutamate rich protein; purification and use in enzyme-linked immunosorbent assay. 203 52

Homologous chromosomes from the human malaria parasite Plasmodium falciparum exhibit striking size polymorphism from isolate to isolate. To examine the structural basis for these variations, we have determined full-length restriction maps of chromosome 4 from three P. falciparum clones. Two clones, HB3 and 3D7, are derived from geographically distant strains, while the third, XP5, is the product of an HB3/3D7 cross. The restriction maps show that, while the overall structure and organization of chromosome 4 from each clone are similar, large-scale variations occur within a few hundred kilobase pairs of the chromosome ends. An apparent crossover between the 3D7 and the HB3 parent chromosomes accounts for a chromosome of intermediate size in clone XP5. Similar restriction studies extended to other parasite chromosomes will ultimately yield a long-range physical map of the P. falciparum genome.
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PMID:Long-range restriction maps of Plasmodium falciparum chromosomes: crossingover and size variation among geographically distant isolates. 307 85

Dihydrofolate reductase (DHFR) (5,6,7,8-tetrahydrofolate: NADPH+-oxidoreductase; EC 1.5.1.3) was partially purified by affinity chromatography from three clones of the human malaria parasite Plasmodium falciparum. The three clones were representative of pyrimethamine-sensitive (clone 3D7) and pyrimethamine-resistant (clone HB3 and clone 7G8) parasites with ID50 values of 0.53 nM (3D7), 210 nM (HB3), and 540 nM (7G8), when tested in vitro against the drug. The specific activities of the partially purified DHFR differed by less than a factor of 2 between the sensitive clone 3D7 (442 +/- 39 nmol min-1 mg-1 protein) and the resistant clones HB3 (634 +/- 25 nmol min-1 mg-1 protein) and 7G8 (565 +/- 85 nmol min-1 mg-1 protein). The number of catalytic sites in partially purified DHFR from the three clones was similar and ranged from 151 to 194 pmol mg-1 protein. The Km value for NADPH was similar in all three clones (4.5-11.6 microM). The Km value for dihydrofolate was altered 13-fold comparing the sensitive clone 3D7 (3.2 +/- 0.6 microM) with the resistant clone HB3 (42.6 +/- 1.6 microM), with the Km for the resistant clone 7G8 falling in between (11.9 +/- 1.2 microM). The inhibition constants for pyrimethamine increased from 0.19 +/- 0.08 nM (3D7) to 2.0 +/- 0.3 nM (HB3) to 8.9 +/- 0.8 nM (7G8). The inhibition by pyrimethamine of the sensitive clone 3D7 was noncompetitive and competitive for the two other clones. The titration of partially purified DHFR with pyrimethamine revealed a 500-fold increase in the concentration of the drug needed to inhibit the DHFR activity by 50%, when the sensitive clone 3D7 (0.18 +/- 0.02 nM) was compared to the resistant clone 7G8 (95 +/- 16 nM). From the comparison of the specific activities and the catalytic center activities with the Km values for the substrate and the inhibition constants for pyrimethamine, both of which are altered in the resistant clones, we conclude that the molecular mechanism for pyrimethamine resistance in the three clones studied is not based on an overproduction of the DHFR but is due to a decreased affinity to antifolates by a structurally altered enzyme.
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PMID:Kinetic and molecular properties of the dihydrofolate reductase from pyrimethamine-sensitive and pyrimethamine-resistant clones of the human malaria parasite Plasmodium falciparum. 355 92

Cytoadherence to HB3 and FC27 strains of Plasmodium falciparum-parasitized red blood cells (PRBC) was studied under shear conditions to elucidate the pathways of adherence to microvascular endothelial cells (MEC). HB3 PRBC bound exclusively to MEC CD36 and intercellular adhesion molecule-1 (ICAM-1) receptors. FC27 PRBC bound to CD36 and another unidentified pathway but not to ICAM-1. Down-regulation of CD36 and ICAM-1 expression by phorbol 12,13-dibutyrate abolished HB3 PRBC adherence. Selective up-regulation of CD36 with interferon-gamma (IFN-gamma) increased PRBC adherence. Conversely, selective up-regulation of ICAM-1 with tumor necrosis factor did not elevate cytoadherence. These data have defined the relative contributions of both CD36 and ICAM-1 to PRBC binding to MEC and have provided evidence for the presence of a novel adhesion mechanism. Furthermore, in addition to antibody blocking of cell adhesion molecules, anti-IFN-gamma antibody therapy or pharmacologic manipulation of endothelial cell receptor expression may reduce PRBC sequestration and ameliorate the events associated with human cerebral malaria.
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PMID:Cytoadherence of Plasmodium falciparum-infected erythrocytes to microvascular endothelium is regulatable by cytokines and phorbol ester. 768 61

Invasion of erythrocytes by malaria parasites involves multiple receptor-ligand interactions. To elucidate these pathways, we made use of four parasite clones with differing specificities for invasion, erythrocytes that are mutant for either glycophorin A or B, and enzyme modification of the erythrocyte surface with neuraminidase and trypsin. Neuraminidase alone abolishes invasion of two parasite clones (Dd2, FCR3/A2); these invade after trypsin treatment alone. A third clone (7G8) is unable to invade trypsin-treated erythrocytes. The fourth clone (HB3) can invade after either neuraminidase or trypsin treatment. The receptor for invasion of trypsin-treated erythrocytes was explored in two ways: treatment of trypsin-treated normal cells with neuraminidase, and trypsin treatment of glycophorin B-deficient cells. Both treatments eliminated invasion by all clones, indicating that the trypsin-independent pathway uses sialic acid and glycophorin B. To identify parasite proteins involved in the different pathways, erythrocyte binding assays were performed with soluble parasite proteins from each clone. Based on binding assays using erythrocytes that lack glycophorin A, the parasite protein known as EBA-175 appears to bind predominantly to glycophorin A. In contrast, the glycophorin B pathway does not appear to involve EBA-175, as binding of EBA-175 was similarly reduced to trypsin-treated normal and trypsin-treated glycophorin B-deficient erythrocytes. Thus, the glycophorin B-dependent, sialic acid-dependent invasion of trypsin-treated normal erythrocytes uses a different parasite ligand, indicating two or more sialic-dependent pathways for invasion. Clone 7G8, which cannot invade trypsin-treated erythrocytes, may be missing the ligand for invasion via glycophorin B.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Glycophorin B as an EBA-175 independent Plasmodium falciparum receptor of human erythrocytes. 807 23

Malarial parasites have two highly conserved cytoplasmic DNA molecules: a 6-kb tandemly arrayed DNA that has characteristics of a mitochondrial genome, and a 35-kb circular DNA that encodes functions commonly found in chloroplasts. We examined the inheritance pattern of these elements in two genetic crosses of Plasmodium falciparum clones. Parent-specific oligonucleotide probes and single-strand conformation polymorphism analysis identified single nucleotide changes that distinguished the parental 6- and 35-kb DNA molecules in the progeny. In all 16 independent recombinant progeny of a cross between a Central American clone, HB3, and a Southeast Asian clone, Dd2, the 6- and 35-kb DNAs were inherited from the Dd2 parent. In all nine independent recombinant progeny of a cross between clone HB3 and a likely African clone, 3D7, the 6-kb DNA was inherited from the 3D7 parent. Inheritance of cytoplasmic genomes of the Dd2 and 3D7 parents was, therefore, dominant over that of the HB3 parent. Cytoplasmic DNA molecules were found almost exclusively in the female gametes of malarial parasites; hence, clone HB3 did not appear to have served as a maternal parent for the progeny of two crosses. Defective differentiation into male gametes by clone Dd2 is likely to be a reason for the cytoplasmic inheritance pattern seen in the HB3 x Dd2 cross. However, incompetence of male or female gametes is unlikely to explain the uniparental dominance in recombinant progeny of the HB3 x 3D7 cross, since both parents readily self-fertilized and completed the malaria life cycle on their own. Instead, the data suggest unidirectional parental incompatibility in cross-fertilization of these malarial parasites, where a usually cosexual parental clone can participate only as a male or as a female. Such an incompatibility may be speculated as indicating an early phase of reproductive isolation of P. falciparum clones from different geographical regions.
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PMID:Unidirectional dominance of cytoplasmic inheritance in two genetic crosses of Plasmodium falciparum. 824 55

Two clones of the human malaria parasite Plasmodium falciparum, denoted 3D7 and HB3, were grown in vitro under conditions permitting the development of gametocytes. The two clones differ in their allelic forms of two antigen genes MSP1 and MSP2. The alleles can be distinguished as size differences of polymerase chain reaction (PCR) amplified fragments of repetitive regions of each gene. Mosquitoes (Anopheles stephensi) were fed on a mixture of these gametocytes. A total of 128 oocysts was isolated from the midguts of infected mosquitoes from 9 crossing experiments between the clones. DNA extracted from these oocysts was amplified by PCR. Oocysts which contained both alleles of each gene (MSP1 and MSP2) had developed from heterozygotes produced by cross-fertilization events between 3D7 and HB3 gametes. The remaining oocysts contained single alleles of each gene, in parent clone combinations, and these had developed from homozygotes formed by self-fertilizations. The results suggest that gametes in the original mixture fed to mosquitoes had undergone random mating.
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PMID:Frequency of cross-fertilization in the human malaria parasite Plasmodium falciparum. 835 94

Sulfated proteoglycans have been shown to be involved in the binding of sporozoites of malaria parasites to hepatocytes. In this study, we have evaluated the effect of sulfated glycosaminoglycans on the invasion of erythrocytes by Plasmodium falciparum merozoites and cytoadherence of parasitized erythrocytes (PRBC) to endothelial cells. Invasion of erythrocytes by HB3EC-6 (an HB3 line selected for high binding to endothelial cells) was inhibited by dextran sulfate 500K, dextran sulfate 5K, sulfatides, fucoidan, and heparin but not by chondroitin sulfate A. With the exception of sulfatides, the invasion-inhibitory effect was not mediated by killing of parasites. Cytoadherence of HB3EC-6 to human microvascular endothelial cells (HMEC-1) and inhibited by these sulfated glycoconjugates. The highly sulfated dextran sulfate 500K had the highest inhibitory effect on both invasion and cytoadherence, whereas the positively charged protamine sulfate promoted cytoadherence. Because preincubation of PRBC with sulfated glycosaminoglycans and treatment of target cells with heparinase had no significant inhibition on cytoadherence, it is unlikely that sulfated glycoconjugates are used directly by endothelial cells as cytoadhesion receptors. In an vivo experiment, we found that the administration of dextran sulfate 500K to CBA/Ca mice infected with Plasmodium berghei ANKA reduced parasitemia and delayed the death associated with anemia. These observations suggest that sulfated polyanions inhibit the invasion of erythrocytes by merozoites and cytoadherence of PRBC to endothelial cells by increasing negative repulsive charge and sterically interfering with the ligand-receptor interaction after binding to target cells.
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PMID:Sulfated polyanions inhibit invasion of erythrocytes by plasmodial merozoites and cytoadherence of endothelial cells to parasitized erythrocytes. 860 3

Several artemisinin derivatives linked to benzylamino and alkylamino groups were synthesized in order to enhance accumulation within the malaria parasite. The in vitro antimalarial activity was assessed against the chloroquine sensitive HB3 strain and the chloroquine resistant K1 strain of Plasmodium falciparum. In general the incorporation of amino functionality enhances the activity relative to artemisinin. The most potent analogue in the series was compound 6 which was severalfold more active than artemisinin against both strains of P. falciparum used in the study.
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PMID:Mechanism-based design of parasite-targeted artemisinin derivatives: synthesis and antimalarial activity of benzylamino and alkylamino ether analogues of artemisinin. 889 47

Sulfadoxine/pyrimethamine (Fansidar) is widely used in Africa for treating chloroquine-resistant falciparum malaria. To clarify how parasite resistance to this combination arises, various lines of Plasmodium falciparum were used to investigate the role of naturally occurring mutations in the target enzyme, dihydropteroate synthetase (DHPS), in the parasite response to sulfadoxine inhibition. An improved drug assay was employed to identify a clear correlation between sulfadoxine-resistance levels and the number of DHPS mutations. Moreover, tight linkage was observed between DHPS mutations and high-level resistance in the 16 progeny of a genetic cross between sulfadoxine-sensitive (HB3) and sulfadoxine-resistant (Dd2) parents. However, we also demonstrate a profound influence of exogenous folate on IC50 values, which, under physiological conditions, may have a major role in determining resistance levels. Importantly, this phenotype does not segregate with dhps genotypes in the cross, but shows complete linkage to the two alleles of the dihydrofolate reductase (dhfr) gene inherited from the parental lines. However, in unrelated lines, this folate effect correlates less well with DHFR sequence, indicating that the gene responsible may be closely linked to dhfr, rather than dhfr itself. These results have major implications for the acquisition of Fansidar resistance by malaria parasites.
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PMID:Sulfadoxine resistance in the human malaria parasite Plasmodium falciparum is determined by mutations in dihydropteroate synthetase and an additional factor associated with folate utilization. 907 34


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