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)

The malaria parasite affects millions of people each year, lives and multiplies in two different hosts, and synthesizes a large number of proteases and heat shock proteins (HSPs) for its survival. We describe here the characterization of a metalloprotease activity which resides in the small HSP (PVHSP28) of the common but noncultivable human malaria parasite Plasmodium vivax. The protein is expressed by erythrocytic stages of the parasite. It is expressed as a approximately 55-kDa polypeptide which is then processed to the 28-kDa mature protein. The latter was found to be an active protease in gelatin zymography. This protease showed its optimal activity at 37 degrees C (pH 7.6). It also retained its proteolytic activity at higher temperatures of up to 55 degrees C. The enzyme belongs to the metalloprotease class, as its proteolytic activity was most effectively blocked by 1,10-phenanthroline and was restored to a maximal level by the addition of zinc metal ions. Inhibitors for the cysteine, serine, and aspartate classes of proteases were ineffective against this enzyme. A homology search indicates that PVHSP28 probably belongs to a new class of HSPs which possess the metalloprotease signature sequence.
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PMID:Metalloprotease activity in a small heat shock protein of the human malaria parasite Plasmodium vivax. 1067 27

We describe the design and synthesis of a novel well characterized multi-peptide conjugate (MPC) system containing antigens from human malaria parasite and the Tat protein of HIV type-1 (HIV-1-Tat). Construction of the MPC utilizes Fmoc solid-phase peptide synthesis coupled with solution chemistry. In the first phase, a core template that serves as primary anchor for the synthesis and attachment of multiple antigens is synthesized. Serine(trityl) and multiple lysine branches with epsilon groups blocked during chain assembly are incorporated forming a tetrameric core. Cysteine whose side chain thiol serves to couple haloacetyl or S-protected haloacetyl peptides is added to complete assembly of the core template. Modification to the coupling solvent, addition of key amino acid derivatives (N-[1-hydroxy-4-methoxybenzyl]) in the peptide sequence allows the synthesis of base peptides on the core template with molecular mass greater than 7500 kDa. Base peptides are then reacted with high performance liquid chromatography purified haloacetyl peptides to generate multiple peptide conjugates with molecular masses of 10 to 13 kDa. MPC constructs thus formed are further characterized by matrix assisted laser desorption-time of flight mass spectroscopy (MALDI-MS), amino acid analysis, size exclusion chromatography, and SDS-polyacrylamide gel electrophoresis (PAGE). To our knowledge, this is the first report describing a chemically well defined multiple conjugate system with potential for development of synthetic subunit vaccines.
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PMID:Synthesis and construction of a novel multiple peptide conjugate system: strategy for a subunit vaccine design. 1070 14

The 175-kDa Plasmodium falciparum erythrocyte binding protein (EBA-175) binds to its receptor, sialic acids on glycophorin A. The binding region within EBA-175 is a cysteine-rich region identified as region II. Antibodies against region II block the binding of native EBA-175 to erythrocytes. We identified a P. falciparum strain, FVO, that could not invade erythrocytes devoid of sialic acids due to prior neuraminidase treatment, and in addition, we used a strain, 3D7, that could invade such sialic acid-depleted erythrocytes. We used these two strains to study the capacity of anti-region II antibodies to inhibit FVO and 3D7 parasite development in vitro. Analysis of growth-inhibitory effects of purified FVO anti-region II immunoglobulin G (IgG) with the FVO and 3D7 strains resulted in similar levels of growth inhibition. FVO and 3D7 strains were inhibited between 28 and 56% compared to control IgG. There appeared to be no intracellular growth retardation or killing of either isolate, suggesting that invasion was indeed inhibited. Incubation of recombinant region II with anti-region II IgG reversed the growth inhibition. These results suggest that antibodies against region II can also interfere with merozoite invasion pathways that do not involve sialic acids. The fact that EBA-175 has such a universal and yet susceptible role in erythrocyte invasion clearly supports its inclusion in a multivalent malaria vaccine.
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PMID:Antibodies against the Plasmodium falciparum receptor binding domain of EBA-175 block invasion pathways that do not involve sialic acids. 1072 89

Advances in combinatorial chemistry, high-throughput screening, and molecular modeling have revolutionized the process of drug discovery in the pharmaceutical industry. Drug discovery efforts for the primary protozoal parasitic diseases of the developing world, malaria, leishmaniasis, and trypanosomiasis, have also begun to employ these techniques. Drug targets in these parasites, exemplified by cysteine proteases and trypanothione reductase, have been purified and used for inhibitor screening. Through this work, small molecules have been identified that inhibit both parasite proteins and the growth of the organisms. This review describes advances that have been made in examining the effects of small molecules on potential parasitic drug targets determined by biochemical and computer-based screening, and also details the activity of such compounds on parasites in vitro and in vivo. Based on these results, it is apparent that modern drug discovery techniques hold promise for the identification of antiparasitic drug candidates.
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PMID:Target-based drug discovery for malaria, leishmaniasis, and trypanosomiasis. 1082 90

Sp22D, a modular serine protease encompassing chitin binding, low density lipoprotein receptor, and scavenger receptor cysteine-rich domains, was identified by molecular cloning in the malaria vector, Anopheles gambiae. It is expressed in multiple body parts and during much of development, most intensely in hemocytes. The protein appears to be posttranslationally modified. Its integral, putatively glycosylated form is secreted in the hemolymph, whereas a smaller form potentially generated by proteolytic processing is associated with the tissues. Bacterial challenge or wounding result in low-level RNA induction, but the protein does not bind to bacteria, nor is its processing affected by infection. However, Sp22D binds to chitin with high affinity and undergoes transient changes in processing during pupal to adult metamorphosis; it may respond to exposure to naked chitin during tissue remodeling or damage.
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PMID:A modular chitin-binding protease associated with hemocytes and hemolymph in the mosquito Anopheles gambiae. 1086 Sep 81

Erythrocytes infected with mature forms of Plasmodium falciparum do not circulate but are withdrawn from the peripheral circulation; they are bound to the endothelial lining and to uninfected erythrocytes in the microvasculature. Blockage of the blood flow, hampered oxygen delivery, and severe malaria may follow if binding is excessive. The NH(2)-terminal head structure (Duffy binding-like domain 1 [DBL1alpha]-cysteine-rich interdomain region [CIDR1alpha]) of a single species of P. falciparum erythrocyte membrane protein 1 (PfEMP1) is here shown to mediate adherence to multiple host receptors including platelet-endothelial cell adhesion molecule 1 (PECAM-1)/CD31, the blood group A antigen, normal nonimmune immunoglobulin M, three virulence-associated receptor proteins, a heparan sulfate-like glucosaminoglycan, and CD36. DBL2delta was found to mediate additional binding to PECAM-1/CD31. The exceptional binding activity of the PfEMP1 head structure and its relatively conserved nature argues that it holds an important role in erythrocyte sequestration and therefore in the virulence of the malaria parasite.
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PMID:The semiconserved head structure of Plasmodium falciparum erythrocyte membrane protein 1 mediates binding to multiple independent host receptors. 1088 May 21

Trophozoites of the malaria parasite Plasmodium falciparum hydrolyze erythrocyte hemoglobin in an acidic food vacuole to provide amino acids for parasite protein synthesis. Cysteine protease inhibitors block hemoglobin degradation, indicating that a cysteine protease plays a key role in this process. A principal trophozoite cysteine protease was purified by affinity chromatography. Sequence analysis indicated that the protease is encoded by a previously unidentified gene, falcipain-2. Falcipain-2 was predominantly expressed in trophozoites, was concentrated in food vacuoles, and was responsible for at least 93% of trophozoite soluble cysteine protease activity. A construct encoding mature falcipain-2 and a small portion of the prodomain was expressed in Escherichia coli and refolded to active enzyme. Specificity for the hydrolysis of peptide substrates by native and recombinant falcipain-2 was very similar, and optimal at acid pH in a reducing environment. Under physiological conditions (pH 5.5, 1 mm glutathione), falcipain-2 hydrolyzed both native hemoglobin and denatured globin. Our results suggest that falcipain-2 can initiate cleavage of native hemoglobin in the P. falciparum food vacuole, that, following initial cleavages, the protease plays a key role in rapidly hydrolyzing globin fragments, and that a drug discovery effort targeted at this protease is appropriate.
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PMID:Characterization of native and recombinant falcipain-2, a principal trophozoite cysteine protease and essential hemoglobinase of Plasmodium falciparum. 1088 94

Various pathogenic bacteria, viruses, and protozoan bind to glycosaminoglycan-based receptors on host cells and initiate an infection. Sporozoites of Plasmodium predominantly express circumsporozoite (CS) protein on their surface, which binds to heparan sulfate proteoglycans on liver cell surface that subsequently leads to malaria. Here we show that the interaction of free heparin with this parasite ligand has the potential to be a critical component of invasion. CS protein of P. falciparum contains four cysteines at positions 361, 365, 396, and 401. In this study, all four cysteine residues were mutagenized to alanine both individually and in different combinations. Conversion of cysteine 396 to alanine (protein CS3) led to a 10-fold increase in the binding activity of the protein to HepG2 cells. Replacement of cysteines at positions 361, 365, and 401 either alone or in different combinations led to a near total loss of binding. Surprisingly, activity in these inactive mutants could be effectively restored in the presence of submolar concentrations of heparin. Heparin also up-regulated binding of CS3 at submolar concentrations with respect to the protein but down-regulated binding when present in excess. Given the significantly different concentrations of heparin in different organs of the host and the in vitro results described here one can consider in vivo ramifications of this phenomenon for pathogen targeting of specific organs and for the functional effects of antigenic variation on receptor ligand interaction.
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PMID:Role of cysteines in Plasmodium falciparum circumsporozoite protein: interactions with heparin can rejuvenate inactive protein mutants. 1089 Sep 3

Adherence of erythrocytes infected with mature asexual Plasmodium falciparum parasites (iRBC) to microvascular endothelial cells contributes to the pathology of P. falciparum malaria. It has been shown that the variant P. falciparum erythrocyte membrane protein 1 (PfEMP1) confers adhesion to a wide range of cell surface receptors. Previously, the cysteine-rich interdomain region (CIDR) of PfEMP1 has been identified as binding site to CD36. We provide evidence that the same region can also mediate binding to chondroitin sulfate A (CSA). CIDR domains of two different parasite strains were expressed in Escherichia coli as a 6xHis-tagged protein. Purified recombinant protein bound to Chinese hamster ovary (CHO) cells which naturally express chondroitin sulfate A. Treatment of wild-type CHO cells with chondroitinase ABC reduced binding up to 94.4%. Competitive binding using soluble CSA inhibited binding to CHO cells by up to 100% at 2 mg/ml and by 62.4% at 0.5 mg/ml, whereas 1 mg/ml heparan sulfate had only a little effect (18.1%). In contrast, a recombinant 6xHis-tagged DBL1 domain showed no binding to wild-type CHO cells. Such an approach of analyzing various domains of PfEMP1 as recombinant proteins may elucidate their functions and may lead to novel anti-adherence therapeutics, especially for maternal malaria infections.
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PMID:Plasmodium falciparum: cloned and expressed CIDR domains of PfEMP1 bind to chondroitin sulfate A. 1091 Jul 12

Antibodies raised against an Escherichia coli-produced recombinant protein encoding a 76-kDa section (region C) of malaria transmission-blocking vaccine candidate, Pfs230, have previously been shown to significantly reduce the ability of Plasmodium falciparum parasites to infect mosquitoes (71.2-89.8%). To further define the region of the Pfs230 required for transmission-blocking activity, four recombinant proteins each encoding a section of region C (Pfs230 amino acids 443-1132) were produced using the same E. coli expression system and tested for immunogenicity in mice: (i) r230/MBP.C5' encodes the first half of region C (amino acids 443-791, six cysteines); (ii) r230/MBP.CM1 encodes only cysteine motif (CM) 1 (amino acids 583-913, eight cysteines); (iii) r230/MBP.C1.6 (amino acids 453-913, eight cysteines) also includes all of CM1; and (iv) r230/MBP.C2 encodes only CM2 (amino acids 914-1268, 11 cysteines). All the recombinant proteins induced antibodies that recognized parasite-produced Pfs230, but the titre of the Pfs230 specific-antibodies generated varied, C = C1.6 = C5' > CM1 > CM2. Two recombinants, r230/MBP.C5' and r230/MBP.C1.6, induced antibody titres that were equivalent to or greater than the titre generated by r230/MBP.C. However, in contrast to r230/MBP.C, none of the recombinants induced antibodies that effectively blocked parasite infectivity to mosquitoes. This suggests that the inclusion of amino acids 914-1132 is important for the production of the transmission-blocking epitope present in region C.
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PMID:Differential ability of specific regions of Plasmodium falciparum sexual-stage antigen, Pfs230, to induce malaria transmission-blocking immunity. 1097 44


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