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)

Merozoites of malaria parasites have a membrane-bound serine protease whose solubilization and subsequent activity depend on a parasite-derived glycosylphosphatidylinositol-phospholipase C (GPI-PLC). The GPI-degrading activities from both Plasmodium falciparum and Plasmodium chabaudi have been characterized and partially purified by phenylboronate chromatography. They are membrane-bound, developmentally regulated, calcium-independent enzymes and as such they resemble GPI-PLC of Trypanosoma brucei. Furthermore, a T. brucei GPI-PLC-specific monoclonal antibody (mAT3) immunoprecipitates the plasmodial GPI-degrading activity. Thin-layer chromatography is suggestive of two activities: a GPI-PLC and a phospholipase A.
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PMID:Plasmodium falciparum and Plasmodium chabaudi: characterization of glycosylphosphatidylinositol-degrading activities. 131 98

Hexokinase, a key glycolytic enzyme, is involved in the initial phosphorylation reaction of imported glucose and specific blocking of this activity may therefore arrest the development of malaria parasites. We describe here the cloning of a single copy hexokinase gene of Plasmodium falciparum (PfHK) from cDNA or genomic DNA libraries. The deduced amino acid sequence of PfHK has 26% identity with human hexokinase I and its predicted molecular mass assigns it as an invertebrate type isoenzyme of hexokinase. A single 1.5-kb exon is translated from a 3-kb mRNA in asexual stages of the parasite. In contrast to aldolase and GPI, the gene for this glycolytic enzyme is located on chromosome 8. Poly- and monoclonal antibodies against recombinant PfHK support our cloning results at the protein level as they detect a protein of the predicted size and isoelectric point by Western blotting in parasite protein samples. Moreover, polyclonal rabbit IgG against recombinant PfHK partially inhibits the hexokinase activity of a P. falciparum lysate which provides direct proof that the gene cloned encodes hexokinase of the parasite.
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PMID:Molecular analysis of Plasmodium falciparum hexokinase. 147 5

To test whether the requirements for GPI-attachment are the same in mammalian cells and parasitic protozoa, we expressed the GPI-linked variant surface glycoprotein (VSG) of Trypanosoma brucei (T. brucei) in COS cells. Although large amounts of VSG were produced, only a small fraction became GPI-linked. This impaired processing is not due to the VSG ectodomain since replacement of the VSG GPI-signal with that of decay accelerating factor (DAF) produced GPI-linked VSG. Further, whereas fusion of the DAF GPI-signal to the COOH-terminus of human growth hormone (hGH) produces GPI-linked hGH, an analogous fusion using the VSG GPI-signal does not, indicating that the VSG GPI-signal functions poorly in mammalian cells. By constructing chimeric VSG-DAF GPI-signals and fusing them to the COOH-terminus of hGH, we show that of the two critical elements that comprise the GPI-signal--the cleavage/attachment site and the hydrophobic domain--the former is responsible for the impaired activity of the VSG GPI-signal in COS cells. To confirm this, we show that the VSG GPI-signal can be converted to a viable signal for mammalian cells by altering the amino acid configuration at the cleavage/attachment site. We also show that when fused to hGH, the putative GPI-signal from the malaria circumsporozoite (CS) protein produces low levels of GPI-anchored hGH, suggesting that the CS protein is indeed GPI-linked, but that the CS protein GPI-signal, like the VSG-signal, functions poorly in COS cells.
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PMID:The requirements for GPI-attachment are similar but not identical in mammalian cells and parasitic protozoa. 808 Dec 28

The genes encoding merozoite surface protein 4/5 (MSP4/5) from Plasmodium berghei and Plasmodium yoelii have been cloned and completely sequenced. Comparisons of the predicted protein sequences with those of Plasmodium chabaudi MSP4/5 and Plasmodium falciparum MSP4 and MSP5 show general structural similarities. All predicted proteins contain hydrophobic signal sequences, potential GPI attachment sequences and a single epidermal growth factor (EGF)-like domain at the C-terminus. The amino acid sequence of the EGF-like motif is highly conserved in rodent malaria species and also shows a considerable degree of similarity with the EGF-like domains found in the P. falciparum proteins. Both the P. yoelii and P. berghei genes show evidence of both spliced and unspliced mRNA at steady state. This phenomenon is similar to that seen for the P. chabaudi MSP4/5 gene, and is believed to be involved in regulation of protein expression. We describe here the construction of clones expressing full length recombinant protein. Antibodies directed against recombinant MSP4/5 proteins recognize a single polypeptide on parasite material and show crossreactivity between MSP4/5 from different murine malaria species, but do not crossreact with either MSP4 or MSP5 from P. falciparum. The various antisera show reactivity against reduction sensitive epitopes as well as reduction insensitive epitopes.
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PMID:Characterization of the merozoite surface protein 4/5 gene of Plasmodium berghei and Plasmodium yoelii. 1061 6

We describe the expression, in insect cells using the baculovirus system, of two protein fragments derived from the C-terminus of merozoite surface protein 1(MSP-1) of the human malaria parasite Plasmodium falciparum, and their glycosylation and intracellular location. The transport and intracellular localisation of the intact C-terminal MSP-1 fragment, modified by addition of a signal sequence for secretion, was compared with that of a similar control protein in which translation of the GPI-cleavage/attachment site was abolished by insertion of a stop codon into the DNA sequence. Both proteins could only be detected intracellularly, most likely in the endoplasmic reticulum. This lack of transport to the cell surface or beyond, was confirmed for both proteins by immunofluorescence with a specific antibody and characterisation of their N-glycans. The N-glycans had not been processed by enzymes localised in post-endoplasmic reticulum compartments. In contrast to MSP-1, the surface antigen SAG-1 of Toxoplasma gondii was efficiently transported out of the endoplasmic reticulum of insect cells and was located, at least in part, on the cell surface. No GPI-anchor could be detected for either of the MSP-1 constructs or SAG-1, showing that the difference in transport is a property of the individual proteins and cannot be attributed to the lack of a GPI-anchor. The different intracellular location and post-translational modification of recombinant proteins expressed in insect cells, as compared to the native proteins expressed in parasites, and the possible implications for vaccine development are discussed.
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PMID:Processing and localisation of a GPI-anchored Plasmodium falciparum surface protein expressed by the baculovirus system. 1071 26

By motif searching of the unfinished sequences in the Malaria Genome Sequencing Project databases we have identified a novel EGF-like domain-containing protein of Plasmodium falciparum. The sequence lies within a single open reading frame of 1791 bp and is predicted to encode a polypeptide of 597 amino acids. There are hydrophobic regions at the extreme N- and C-termini, which could represent secretory signal peptide and GPI attachment sites, respectively. Similar to MSP1, there are two EGF-like domains located near the C-terminus. RT-PCR analysis of the novel gene shows that it is transcribed in asexual stages of the malaria parasite. We have expressed portions of the protein as recombinant GST fusions in Escherichia coli and raised antisera in rabbits. Antibodies to the EGF-like domains of the novel protein are highly specific and do not cross-react with the EGF-like domains of MSP1, MSP4 or MSP5 expressed as GST fusion proteins. Antiserum raised to the most C-terminal region of the protein reacts with four bands of 98, 50, 25 and 19 kDa in P. falciparum parasite lysates whereas antisera to the N-terminal fusion proteins recognise the 98 and 50 kDa bands, suggesting that the novel protein may undergo processing in a similar way to MSP1. Immunoblot analysis of stage-specific parasite samples reveals that the protein is present throughout the parasite asexual life cycle and in isolated merozoites, with the smaller fragments present in ring stage parasites. The protein partitions in the detergent-enriched phase after Triton X-114 fractionation and is localized to the surfaces of trophozoites, schizonts and free merozoites by indirect immunofluorescence. Antisera to the C-terminus stain the surface of rings, whereas antisera to the N-terminus do not, suggesting that a fragment of the protein is carried into the developing ring stage parasite. Based on the accepted nomenclature in the field we designate this protein MSP8. We have shown that the MSP8 fusion proteins are in a conformation that can be recognised by human immune sera and that there is very limited diversity in the MSP8 gene sequences from various P. falciparum laboratory isolates. MSP8 shows significant similarity to the recently reported sequence of the protective P. yoelii merozoite surface protein pypAg-2 [Burns JM, Belk CC, Dunn PD. Infect Immun 2000;68:6189-95.] suggesting that the two proteins are homologues. Taken together, these findings suggest that MSP8/pypAg-2 may play an important role in the process of red cell invasion and is a potential malaria vaccine candidate.
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PMID:Merozoite surface protein 8 of Plasmodium falciparum contains two epidermal growth factor-like domains. 1137 1

The human malaria parasite, Plasmodium falciparum, has as its only glycoconjugate GPI anchors. These structures, present in essentially all parasite surface proteins, are associated with disease pathology. In contrast, the parasite depends for essential recognition events on saccharides associated with host cell glycoproteins and proteoglycans.
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PMID:Glycobiology of Plasmodium falciparum. 1152 88

Merozoite surface proteins of Plasmodium falciparum are one major group of antigens currently being investigated and tested as malaria vaccine candidates. Two recently described P. falciparum merozoite surface antigens, MSP4 and MSP5, are GPI-anchored proteins that each contain a single EGF-like domain and appear to have arisen by an ancient gene duplication event. The genes are found in tandem on chromosome 2 of P. falciparum and the syntenic region of the genome was identified in the rodent malarias P. chabaudi, P. yoelii and P. berghei. In these species, there is only a single gene, designated MSP4/5 encoding a single EGF-like domain similar to the EGF-like domain in both PfMSP4 and PfMSP5. Immunization of mice with PyMSP4/5 provides mice with high levels of protection against lethal challenge with blood stage P. yoelii. In this study, we show that in P. vivax, which is quite phylogenetically distant from P. falciparum, both MSP4 and MSP5 homologues can be found with their relative arrangements with respect to the surrounding genes mostly preserved. However, the gene for MSP2, found between MSP5 and adenylosuccinate lyase (ASL) in P. falciparum, is absent from P. vivax. The PvMSP4 and PvMSP5 genes have a two-exon structure and encode proteins with potential signal and GPI anchor sequences and a single EGF-like domain near the carboxyl-terminus. Rabbit antisera raised against purified recombinant proteins show that each of the antisera react with distinct proteins of 62 kDa for PvMSP4 and 86 kDa for PvMSP5 in parasite lysates. Indirect immunofluorescence assays (IFA) localized PvMSP4 over the entire surface of P. vivax merozoites, as expected, whereas, the MSP5 homologue was found to be associated with an apical organellar location consistent with micronemes or over the polar prominence.
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PMID:The Plasmodium vivax homologues of merozoite surface proteins 4 and 5 from Plasmodium falciparum are expressed at different locations in the merozoite. 1189 27

NO overproduction has been suggested to contribute to the immunopathology related to malaria infection. Even though a role for some parasite molecules (e.g., GPI) in NO induction has been proposed, the direct contribution of hemozoin (HZ), another parasite metabolite, remains to be established. Therefore, we were interested to determine whether Plasmodium falciparum (Pf) HZ and synthetic HZ, beta-hematin, alone or in combination with IFN-gamma, were able to induce macrophage (Mphi) NO synthesis. We observed that neither Pf HZ nor synthetic HZ led to NO generation in B10R murine Mphi; however, they significantly increased IFN-gamma-mediated inducible NO synthase (iNOS) mRNA and protein expression, and NO production. Next, by investigating the transductional mechanisms involved in this cellular regulation, we established that HZ induces extracellular signal-regulated kinase (ERK)1/2 mitogen-activated protein kinase phosphorylation as well as NF-kappaB binding to the iNOS promoter, and enhances the IFN-gamma-dependent activation of both second messengers. Of interest, cell pretreatment with specific inhibitors against either NF-kappaB or the ERK1/2 pathway blocked the HZ + IFN-gamma-inducible NF-kappaB activity and significantly reduced the HZ-dependent increase on IFN-gamma-mediated iNOS and NO induction. Even though selective inhibition of the Janus kinase 2/STAT1alpha pathway suppressed NO synthesis in response to HZ + IFN-gamma, HZ alone did not activate this signaling pathway and did not have an up-regulating effect on the IFN-gamma-induced Janus kinase 2/STAT1alpha phosphorylation and STAT1alpha binding to the iNOS promoter. In conclusion, our results suggest that HZ exerts a potent synergistic effect on the IFN-gamma-inducible NO generation in Mphi via ERK- and NF-kappaB-dependent pathways.
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PMID:Hemozoin increases IFN-gamma-inducible macrophage nitric oxide generation through extracellular signal-regulated kinase- and NF-kappa B-dependent pathways. 1453 Mar 48

Ligandless palladium-catalyzed Suzuki-Miyaura coupling converted an inert p-bromobenzyl ether to a DDQ-labile p-(3,4-dimethoxyphenyl) benzyl ether in the presence of azide functionality and this strategy serves as a key step for the convergent synthesis of a fully lipidated malaria GPI disaccharide.
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PMID:A Suzuki-Miyaura coupling mediated deprotection as key to the synthesis of a fully lipidated malarial GPI disaccharide. 1527 48


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