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Query: UMLS:C0024530 (malaria)
 44,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study investigates protein glycosylation in the asexual intraerythrocytic stage of the malaria parasite, Plasmodium falciparum, and the presence in the infected erythrocyte of the respective precursors. In in vitro cultures, P. falciparum can be metabolically labeled with radioactive sugars, and its multiplication can be affected by glycosylation inhibitors, suggesting the capability of the parasite to perform protein-glycosylation reactions. Gel-filtration analysis of sugar-labeled malarial proteins before and after specific cleavage of N-glycans or O-glycans, respectively, revealed the majority of the protein-bound sugar label to be incorporated into O-glycans, but only little (7-12% of the glucosamine label) or no N-glycans were found. Analysis of the nucleotide sugar and sugar-phosphate fraction showed that radioactive galactose, glucosamine, fucose and ethanolamine were converted to their activated derivatives required for incorporation into protein. Mannose was mainly recovered as a bisphosphate, whereas the level of radiolabeled GDP-mannose was below the detection limit. The analysis of organic-solvent extracts of sugar-labeled cultures showed no evidence for the formation by the parasite of dolichol cycle intermediates, the dedicated precursors in protein N-glycosylation. Consistently, the amount of UDP-N-acetylglucosamine formed did not seem to be affected by the presence of tunicamycin in the culture. Oligosaccharyl-transferase activity was not detectable in a lysate of P. falciparum, using exogenous glycosyl donors and acceptors. Our studies show that O-glycosylation is the major form of protein glycosylation in intraerythrocytic P. falciparum, whereas there is little or no protein N-glycosylation. A part of these studies has been published in abstract form [Dieckmann-Schuppert, A., Hensel, J. and Schwarz, R. T. (1991) Biol. Chem. Hoppe-Seyler 372, 645].
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PMID:Apparent lack of N-glycosylation in the asexual intraerythrocytic stage of Plasmodium falciparum. 137 32

Merozoites of the human malaria parasite Plasmodium falciparum express on their surface several antigens derived from a polymorphic glycoprotein precursor of Mr 185,000 synthesised earlier on by trophozoites and schizonts. A panel of 18 monoclonal antibodies against a range of different specificities of the precursor was used to characterise its mature products in spontaneously released merozoites. Merozoites released by [35S]methionine or [14C]glucosamine-labelled schizonts, or surface 125I-labelled purified merozoites, were extracted in detergents, and the antigens were detected by immunoprecipitation or Western blotting. We show that a nonglycosylated peptide of Mr 80,000 and two glycosylated fragments of Mr 40,000 and Mr 16,000, all derived from the precursor, are exposed on the surface of the mature merozoite. Precipitations from extracts in different detergents indicate that the 80 and 40 kDa fragments can form a non-covalent complex with each other and two additional major surface antigens of 36 and 22 kDa. Several antibodies react strongly with the complex but not with its dissociated subunits, thus indicating presence of conformational epitopes. Other epitopes are positively mapped on different dissociated subunits by immunoprecipitation and Western blotting. The 80 and 40 kDa antigens each carry a different polymorphic marker epitope, and both of these markers are absent on the 16 kDa fragment. The 40 and 16 kDa glycoproteins share common epitopes, and the latter may be derived from the former fragments. Only epitopes present on the 16 kDa antigen, but not those specific for the larger fragments, are detectable by immunofluorescence in the ring-stage. This indicates that the whole or a part of the 16 kDa antigen remains on the parasite through the invasion process.
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PMID:Fragments of the polymorphic Mr 185,000 glycoprotein from the surface of isolated Plasmodium falciparum merozoites form an antigenic complex. 243 53

Supernatants from Epstein-Barr virus (EBV)--stimulated B lymphocytes obtained from two adult Gambians who were partially immune to malaria markedly inhibited the growth of Plasmodium falciparum in vitro (55-95% inhibition). When 22 separate colonies were derived by micromanipulation from one of these primary cultures and their supernatants assayed, the degree of inhibition correlated with levels of IgG fluorescent antibody and total IgG. The inhibitory anti-P. falciparum IgG immunoprecipitated an antigen of mol. wt 195,000, identified as the major schizont surface glycoprotein by dual biosynthetic labelling with 3H-glucosamine or 35S-methionine. Other studies on the analogous schizont surface protein of rodent malarias have shown that this antigen stimulates protective immunity. Production of this inhibitory antibody by adult Gambians may therefore contribute to their immunity to malaria. Human antibodies produced by EBV-stimulated B lymphocytes may be used to identify other important P. falciparum antigens and have potential applications for immunotherapy.
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PMID:Inhibition of Plasmodium falciparum growth by IgG antibody produced by human lymphocytes transformed with Epstein-Barr virus. 300 52

Vaccination trials have shown that a purified, 74 kDa glycoprotein, GP74, isolated from the host cell membrane of Plasmodium knowlesi-infected rhesus erythrocytes, can provide protective immunity against P. knowlesi malaria. We have extended this work by a tryptic peptide analysis of the disposition of GP74 in the host cell membrane. Of the 18 peptides characterized by high-performance liquid chromatography only four were accessible to lactoperoxidase-catalyzed radioiodination of non-leaky, schizont-infected host cells from the extracellular space. Metabolic labeling with radioactive glucosamine indicates that two of the surface exposed peptides are glycopeptides, and one of these, peptide 12 appears to carry a dominant antigenic site, according to its reactivity with immunoglobulin from sera of monkeys protected against P. knowlesi malaria.
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PMID:Membrane orientation and antigenic peptides of an immunoprotective 74 kDa Plasmodium knowlesi glycoprotein. 373 96

The capacity of Plasmodia to synthesize sialic acids was investigated by adding radioactive acetate to short-term in vitro cultures of the intraerythrocytic asexual forms of three malaria parasites (the human malaria Plasmodium falciparum in Aotus trivirgatus erythrocytes; the simian malaria P. knowlesi in rhesus monkey erythrocytes; the rodent malaria P. berghei in mouse erythrocytes) and to cultures of extracellular zygotes of the avian malaria P. gallinaceum. Radioactive acetate was added to normal rhesus monkey erythrocytes and to cells of the murine myeloma NS-1 for comparison. Although [1-14C]-acetate labeled many proteins with each malaria parasite and the NS-1 cells, analysis of purified sialic acids revealed that only with the NS-1 cells was radioactivity incorporated into sialic acids. Furthermore, N-acetyl[6-3H]mannosamine was not incorporated into sialic acids or malarial glycoproteins when added to P. knowlesi cultures. All of the malaria parasites underwent growth or differentiation during these experiments as measured by [35S]methionine uptake into protein and by light microscopy. Extracellular parasites largely free of erythrocyte membranes were prepared to determine whether Plasmodia contain sialic acids that are not labeled by exogenous precursors. Purified merozoites of P. knowlesi and zygotes of P. gallinaceum did not contain detectable amounts of sialic acids on chemical analysis. Thus, although we could show that Plasmodia can incorporate radioactive sugars such as glucosamine, galactose and mannose into proteins, presumably glycoproteins, they do not synthesize sialic acids or sialo-glycoproteins, nor do they contain sialo-glycoconjugates of host origin.
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PMID:Malaria parasites do not contain or synthesize sialic acids. 637 Aug 20

Membrane glycoprotein synthesis by Plasmodium falciparum was determined by metabolic labelling in the presence of 74 kBq/ml (2.5 muCi/ml) glucosamine-(3)H. Five major glycoprotein bands and four minor ones were demonstrated. A control experiment using normal, outdated, human erythrocytes indicates that there was no incorporation of the labelled glucosamine into the erythrocyte membrane. It was also demonstrated that the rate of membrane glycoprotein synthesis by mature parasites of the trophozoite and schizont stages was twice that of the ring-stage parasites. Cytochemical surface-labelling experiments had led to the conclusion that the membrane of malaria parasites contains little or no glycoprotein. Our studies indicate, however, that there is significant synthesis of membrane glycoprotein by the parasite and that this can be metabolically labelled and measured by using radioactive glucosamine as precursor of the glycoprotein.
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PMID:Labelling of membrane glycoproteins of cultivated Plasmodium falciparum. 699 92

In the course of an investigation of hexosamine catabolism in the human malaria parasite, Plasmodium falciparum, it became apparent that a basic understanding of the relevant enzymatic reactions in the host erythrocyte is lacking. To acquire the necessary basic knowledge, we have determined the activities of several enzymes involved in hexosamine metabolism in normal human red blood cells. In the present communication we report the results of studies of glucosamine 6-phosphate deaminase (GlcN6-P) using a newly developed sensitive radiometric assay. The mean specific activity in extracts of fresh erythrocytes assayed within 4h of collection was 14.7 nmol/h/mg protein, whereas preparations from older erythrocytes that had been stored at 4 degrees C for up to 4 weeks had a mean specific activity of 6.2 nmol/h/mg. Characterization of the deaminase by chromatofocusing gave a pI of 8.55. The enzyme was optimally active at pH 9.0 and had a Km of 41 microM. The metal chelators EDTA and EGTA were non-inhibitory; however, inhibition was observed in the presence of metal ions, especially Cu2+, Ni2+ and Zn2+. In addition, the deaminase was also inhibited by several sugar phosphates including the reaction product, fructose 6-phosphate.
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PMID:Glucosamine 6-phosphate deaminase in normal human erythrocytes. 757 55

Plasmodium falciparum is the causative agent of malaria tropica in man. Biochemical studies were focused on the asexual, intraerythrocytic stages of P. falciparum, because of their role in the clinical phase of the disease and the possibility of propagation in a cell culture system. In this report, we describe the in-culture labeling of malarial glycolipids and the analysis of their hydrophilic moieties. They were identified as glycosylphosphatidylinositols (GPIs) by: 1) labeling with [3H]mannose, [3H]glucosamine, and [3H]ethanolamine and 2) sensitivity toward glycosylphosphatidylinositol-specific phospholipase D, phospholipase A2, and nitrous acid. Malarial GPIs are shown to be unaffected by treatment with phosphatidylinositol-specific phospholipase C, regardless of prior treatment with mild base commonly used for inositol deacylation. Two candidates for putative GPI-anchor precursors to malarial membrane proteins with the structures ethanolamine-phosphate-6(Man alpha 1-2)Man alpha 1-2Man alpha 1-6Man alpha 1-4 GlcN-PI (Pfg1 alpha) and ethanolamine-phosphate-6Man alpha 1-2Man alpha 1-6Man-alpha 1-4-GlcN-PI (Pfg1 beta) were identified.
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PMID:Glycosylphosphatidylinositols synthesized by asexual erythrocytic stages of the malarial parasite, Plasmodium falciparum. Candidates for plasmodial glycosylphosphatidylinositol membrane anchor precursors and pathogenicity factors. 830 May 89

O-Glycosylation is the major form of protein glycosylation in human erythrocytes infected with the asexual intraerythrocytic stage of the malaria parasite. Plasmodium falciparum. This study compares aspects of O-glycosylation in P. falciparum-infected and uninfected erythrocytes. Non-labeled and metabolically glucosamine-labeled O-glycans were obtained from the protein fraction of infected or uninfected erythrocytes by beta elimination. Additional label was introduced by reduction with sodium borohydride, or by the attachment of radioactive Gal to peripheral GlcNAc using galactosyltransferase. 2-4-times more labeled O-glycans were obtained from infected erythrocytes compared to the same number of uninfected ones, consistent with additional biosynthesis by the parasite. Our analysis of these O-glycans showed no significant qualitative divergence between the O-glycans of the infected and those of the uninfected red cell. According to preliminary alditol analyses, the O-glycans of P. falciparum-infected red cells do not contain GalNAc at their reducing terminus. Moreover, GalNAc was not synthesized by P. falciparum from either Glc, Gal, GlcN or GalN. At least one O-glycan found in P. falciparum-infected erythrocytes contains GlcNAc at its reducing terminus. Gel-filtration results had suggested the presence of O-GlcNAc on proteins in the infected erythrocyte. Probing with a synthetic pentapeptide, we could show that P. falciparum expresses its own O-GlcNAc transferase during intraerythrocytic development. Using this peptide, the enzyme was characterized to some degree. The localization and function of O-GlcNAc in P. falciparum remains to be elucidated.
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PMID:Studies on O-glycans of Plasmodium-falciparum-infected human erythrocytes. Evidence for O-GlcNAc and O-GlcNAc-transferase in malaria parasites. 840 96

The pathways of glucose utilization for energy production in the malaria parasite, Plasmodium falciparum, have been studied extensively. Little is known, however, about the reactions by which glucose is converted into complex carbohydrates in the parasite, and knowledge of the catabolism of these substances is likewise scanty. The present investigation was undertaken to determine whether the parasites possess a key enzyme of glucosamine catabolism, i.e. glucosamine 6-phosphate deaminase (EC 5.3.1.40), which catalyses the conversion of the sugar phosphate to fructose 6-phosphate and ammonia. Lysates of Plasmodium-infected erythrocytes had substantially higher deaminase activity than control samples from normal erythrocytes, and an even higher specific activity was observed in extracts of isolated parasites, amounting to 20-40 times that of uninfected cells. Anion exchange chromatography indicated that the parasite deaminase eluted in a retarded position when compared to the elution profile of the erythrocyte enzyme. The charge difference suggested by these findings was established more directly by chromatofocusing, which indicated pI values of 6.85 and 8.55 for the parasite and erythrocyte deaminases, respectively. Other differences were also observed, notably a greater thermolability on the part of the parasite enzyme. These results indicated that the parasites synthesize a specific deaminase that is distinct from the normal erythrocyte enzyme. Studies on synchronized parasite cultures further indicated that the parasite deaminase is developmentally regulated, because a dramatic increase in activity levels occurred during the later stages of parasite development.
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PMID:Glucosamine 6-phosphate deaminase in Plasmodium falciparum. 855 58


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