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 immunosuppressive peptide cyclosporin A inhibits the growth of malaria parasites in vitro and in vivo, but little is known about its mechanism of antimalarial action. The immunosuppressive action of cyclosporin A is believed to result from binding of the drug to cyclophilins (intracellular peptidyl-prolyl cis-trans isomerases), and inhibition of the protein phosphatase calcineurin by the cyclosporin A-cyclophilin complex. Two immunosuppressive macrolides, FK506 and rapamycin, bind to a distinct isomerase, FKBP12, and the FK506-FKBP complex also inhibits calcineurin. Calcineurin itself is apparently involved in signal transduction between the T-cell membrane and nucleus, and its inhibition blocks T-cell activation. Rapamycin inhibits a later step in T-cell proliferation. Peptidyl-propyl cis-trans isomerase activity was detected in extracts of Plasmodium falciparum. It was completely inhibited by concentrations of cyclosporin A above 0.1 microM, but not by FK506 or rapamycin, and probably represented one or more cyclophilins. Comparison of the antimalarial and anti-isomerase activities of a series of cyclosporin analogues failed to reveal a correlation between the two properties. Cyclosporin A and its more active 8'-oxymethyl-dihydro-derivative, in combination with the cyclophilin-containing P. falciparum extract, inhibited the protein phosphatase activity of bovine calcineurin. Therefore inhibition of a putative P. falciparum calcineurin by a complex of CsA and cyclophilin might be responsible for the antimalarial action of the drug. The most active cyclosporin, however, was a 3'-keto-derivative of cyclosporin D (SDZ PSC-833) which inhibited P. falciparum growth with a 50% inhibitory concentration (IC50) of 0.032 microM (compared with 0.30 microM for cyclosporin A), but was a poor inhibitor of the parasite isomerase. 3'-Keto-cyclosporin D has negligible immunosuppressive activity, but it strongly inhibits the P-glycoprotein of multi-drug resistant mammalian tumour cells. FK506 and rapamycin were also active antimalarials (IC50 of 1.9 and 2.6 microM, respectively) but in the absence of detectable FKBP in P. falciparum extracts, their mechanisms of antimalarial action remain unclear.
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PMID:Roles of peptidyl-prolyl cis-trans isomerase and calcineurin in the mechanisms of antimalarial action of cyclosporin A, FK506, and rapamycin. 752 Jun 96

The immunosuppressive drug cyclosporin A (CsA) inhibits the growth of malaria parasites in vitro and in vivo. Cyclosporin A exerts its immunosuppressive effect in T lymphocytes by binding to cyclophilin (CyP), a peptidylprolyl cis-trans isomerase (PPIase). It is believed that the cyclosporin/cyclophilin complex inhibits a Ca(2+)-activated protein phosphatase, calcineurin, involved in T-cell activation. A cDNA encoding a cyclophilin of the human malaria parasite Plasmodium falciparum has been isolated as a step in the elucidation of the mechanism of antimalarial action of CsA. This cDNA, termed PfCyP, encodes a protein of 195 amino acids which has highest similarity with the Candida albicans (73.1%) and the Drosophila melanogaster (73.1%) cytoplasmic cyclophilins. A Northern blot reveals an approximately 900-bp nucleotide transcript that is consistent with the predicted size of the encoded polypeptide. The predicted PfCyP protein has a putative endoplasmic-reticulum-directed signal sequence at its N-terminus and two potential N-linked glycosylation sites. Expression of PfCyP RNA in an in vitro translation/translocation system reveals that the PfCyP protein is translocated across microsomes, that the signal peptide is cleaved and that the PfCyP protein is glycosylated at two sites. The PfCyP cDNA open reading frame coding for the predicted mature protein has been expressed in Escherichia coli. The purified recombinant protein is an active PPIase (kcat/Km = 2.3 x 10(6) s-1 M-1); this enzymic activity is inhibited by CsA (IC50 = 10 nM). The PfCyP protein has thus the same sensitivity to CsA as the PPIase activity associated with P. falciparum extracts [Bell, A. et al. (1994) Biochem. Pharmacol. 48, 495-503] suggesting that PfCyP may be responsible for the PPIase activity in those extracts. If different cyclophilins exist in P. falciparum, we conclude that either the PfCyP protein is the major cyclophilin detected in the parasite or that there are other cyclophilins with similar susceptibilities to CsA.
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PMID:Molecular and biochemical characterization of a Plasmodium falciparum cyclophilin containing a cleavable signal sequence. 758 14

Protein phosphatases play a critical role in the regulation of the eukaryotic cell cycle and signal transduction. A putative protein serine/threonine phosphatase gene has been isolated from the human malaria parasite Plasmodium falciparum. The gene has an unusual intron that contains four repeats of 32 nucleotides and displays a high degree of size polymorphism among different strains of P. falciparum. The open reading frame reconstituted by removal of the intron encodes a protein of 466 amino acids with a predicted molecular mass of approximately 53.7 kDa. The encoded protein, termed protein phosphatase beta (PP-beta), is composed of two distinct domains. The C-terminal domain comprises 315 amino acids and exhibits a striking similarity to the catalytic subunits of the type-2A protein phosphatases. Database searches revealed that the catalytic domain has the highest similarity to Schizosaccharomyces pombe Ppa1 (58% identity and 73% similarity). However, it contains a hydrophilic insert consisting of five amino acids. The N-terminal domain comprises 151 amino acid residues and exhibits several striking features, including high levels of charged amino acids and asparagine, and multiple consensus phosphorylation sites for a number of protein kinases. An overall structural comparison of PP-beta with other members of the protein phosphatase 2A group revealed that PP-beta is more closely related to Saccharomyces cerevisiae PPH22. Southern blots of genomic DNA digests and chromosomal separations showed that PP-beta is a single-copy gene and is located on chromosome 9. A 2800-nucleotide transcript of this gene is expressed specifically in the sexual erythrocytic stage (gametocytes). The results indicate that PP-beta may be involved in sexual stage development.
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PMID:Protein phosphatase beta, a putative type-2A protein phosphatase from the human malaria parasite Plasmodium falciparum. 936 59

Two major protein phosphatase (PP) activities were purified from cytosolic extracts of the erythrocytic stage of the malaria parasite, Plasmodium falciparum. Both enzymes were specific for phosphoserine and phosphothreonine residues with very little activity against phosphotyrosine residues. The biochemical properties of the enzymes suggested their strong similarity with eukaryotic PP2A and PP2B protein phosphatases. Both enzymes preferentially dephosphorylated the alpha subunit of phosphorylase kinase, and were resistant to inhibitor-1. The PP2A-like enzyme required Mn2+ for activity and was inhibited by nanomolar concentrations of okadaic acid (OA). The cDNA sequence of the PP2A-like enzyme was identified through a match of its predicted amino acid sequence with the N-terminal sequence of the catalytic subunit. The PP2B-like (calcineurin) enzyme was stimulated by calmodulin and Ca2+ or Ni2+, but was resistant to OA. Malarial calcineurin was strongly and specifically inhibited by cyclosporin A (CsA) only in the presence of wild type P. falciparum cyclophilin but not a mutant cyclophilin. The inhibition was noncompetitive, and provides a potential explanation for the cyclosporin-sensitivity of the parasite. There was no significant quantitative difference in the total protein Ser/Thr phosphatase activity among the ring, trophozoite, and schizont stages.
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PMID:Characterization of protein Ser/Thr phosphatases of the malaria parasite, Plasmodium falciparum: inhibition of the parasitic calcineurin by cyclophilin-cyclosporin complex. 1034 Apr 82

A novel protein phosphatase cDNA of the PPP superfamily was identified from the malaria parasite, Plasmodium falciparum (Pf), and tentatively named PfPPJ. The predicted primary structure of the phosphatase contained all the known conserved motifs of the PPP superfamily essential for catalytic activity. The enzyme was specific for dephosphorylation of phosphoserine and phosphothreonine residues with very little activity against phosphotyrosine residues. However, the sequence at its C-terminal end was unique, and was consistent with its resistance to the classical PP2A-specific inhibitors such as okadaic acid and microcystin-LR, and the PP1-specific inhibitor, mammalian heat-stable inhibitor-2 (I-2). Even the catalytic core of PfPPJ had a sequence substantially different from the other PPPs such that PfPPJ could be placed in an apparently separate phylogenetic branch. At 294 amino acids residues, PfPPJ was one of the smallest okadaic acid-resistant PPP phosphatases known. By Northern blot analysis, the expression of the PfPPJ mRNA showed the following pattern: schizont > ring > trophozoite, which closely paralleled the expression of the protein, as determined by immunofluorescence. Together, these results suggested a parasitic stage-specific transcriptional regulation of this novel and potentially unique protozoan phosphatase.
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PMID:Characterization of a novel serine/threonine protein phosphatase (PfPPJ) from the malaria parasite, Plasmodium falciparum. 1137 37

Geldanamycin (GA), an antibiotic of the ansamycin family and an inhibitor of heat shock protein 90 (Hsp90), was previously shown to inhibit the malarial parasite, Plasmodium falciparum. Here we report that cyclosporin A (CsA), an inhibitor of parasitic cyclophilin (Cyp) and protein phosphatase 2B (calcineurin, CN), acted synergistically with GA to inhibit the erythrocytic growth of the parasite. Parasitic calcineurin associated with Hsp90 in vivo, and GA inhibited the association, but CsA had no effect. In a number of CsA-resistant (CsA(R)) P. falciparum clones mutations were detected in functionally significant amino acid residues of the catalytic and regulatory subunits of calcineurin (CnA and CnB, respectively) and in two out of three parasitic cyclophilins, namely Cyp19A and Cyp19B. No mutation was detected in the third cyclophilin, Cyp24. Further analysis of the mutant CnA revealed that its protein phosphatase activity was highly CsA-resistant in vitro. Similarly, one of the mutant Cyp19A proteins was purified and found to be unable to inhibit parasitic CN in the presence of CsA. Together, these results underscore the importance of the proper assembly and function of CN in plasmodial biology and suggest that the inhibition of CN can be a potential mechanism behind the CsA-sensitivity of the malaria parasite.
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PMID:Plasmodium falciparum calcineurin and its association with heat shock protein 90: mechanisms for the antimalarial activity of cyclosporin A and synergism with geldanamycin. 1581 24

Availability of complete genome sequence for Plasmodium falciparum has been useful in drawing a comprehensive metabolic map of the parasite. Distinct and unique metabolic characteristics of the parasite may be exploited as potential targets for new antimalarial drug discovery research. Reversible phosphorylation of proteins is a ubiquitous process and an indispensable part of cell signaling cascades, which regulate different cellular functions. Not so long ago the role of protein phosphatases in the cell life was underestimated but now these enzymes strongly focus attention of many researches. Based on primary structure and functional characteristics protein phosphatases have been divided into number of families and subfamilies. The amino acid sequences of catalytic subunits of protein phosphatases of particular families stay highly conserved in eukaryotic organisms during evolutionary changes. Serine/threonine protein phosphatases (PPPs) constitute an important family, which are involved in mitotic and meiotic cell divisions, cell development, apoptosis and many other crucial cellular processes. Complex life cycle of the malaria parasite, which encompasses through distinct developmental stages, offers highly sophistical roles for the protein phosphatases. We have researched and analyzed characteristics of 17 putative or/and confirmed catalytic subunits of PPPs on P. falciparum genome. Evidences have been gathered that indicate functional expression of some PPP isoforms in P. falciparum. A few of them have been found to be essential or play important cellular functions in the parasite. Identification of distinct molecular and functional characteristics of these enzymes shall be useful in designing selective inhibitors of plasmodial PPPs as potential new antimalarials.
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PMID:Plasmodium falciparum serine/threonine phoshoprotein phosphatases (PPP): from housekeeper to the 'holy grail'. 1899 11

The highly co-evolved relationship of parasites and their hosts appears to include modulation of host immune signals, although the molecular mechanisms involved in the host-parasite interplay remain poorly understood. Characterization of these key genes and their cognate proteins related to the host-parasite interplay should lead to a better understanding of this intriguing biological phenomenon. The malaria agent Plasmodium falciparum is predicted to export a cohort of several hundred proteins to remodel the host erythrocyte. However, proteins actively exported by the asexual intracellular parasite beyond the host red blood cell membrane (before merozoite egress) have been poorly investigated so far. Here we used two complementary methodologies, two-dimensional gel electrophoresis/MS and LC-MS/MS, to examine the extracellular secreted antigens at asexual blood stages of P. falciparum. We identified 27 novel antigens exported by P. falciparum in the culture medium of which some showed clustering with highly polymorphic genes on chromosomes, suggesting that they may encode putative antigenic determinants of the parasite. Immunolocalization of four novel secreted proteins confirmed their export beyond the infected red blood cell membrane. Of these, preliminary functional characterization of two novel (Sel1 repeat-containing) parasite proteins, PfSEL1 and PfSEL2 revealed that they down-regulate expression of cell surface Notch signaling molecules in host cells. Also a novel protein kinase (PfEK) and a novel protein phosphatase (PfEP) were found to, respectively, phosphorylate/dephosphorylate parasite-specific proteins in the extracellular culture supernatant. Our study thus sheds new light on malaria parasite extracellular secreted antigens of which some may be essential for parasite development and could constitute promising new drug targets.
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PMID:Proteome analysis of Plasmodium falciparum extracellular secretory antigens at asexual blood stages reveals a cohort of proteins with possible roles in immune modulation and signaling. 1949 39

Protein phosphorylation and dephosphorylation (catalysed by kinases and phosphatases, respectively) are post-translational modifications that play key roles in many eukaryotic signalling pathways, and are often deregulated in a number of pathological conditions in humans. In the malaria parasite Plasmodium, functional insights into its kinome have only recently been achieved, with over half being essential for blood stage development and another 14 kinases being essential for sexual development and mosquito transmission. However, functions for any of the plasmodial protein phosphatases are unknown. Here, we use reverse genetics in the rodent malaria model, Plasmodium berghei, to examine the role of a unique protein phosphatase containing kelch-like domains (termed PPKL) from a family related to Arabidopsis BSU1. Phylogenetic analysis confirmed that the family of BSU1-like proteins including PPKL is encoded in the genomes of land plants, green algae and alveolates, but not in other eukaryotic lineages. Furthermore, PPKL was observed in a distinct family, separate to the most closely-related phosphatase family, PP1. In our genetic approach, C-terminal GFP fusion with PPKL showed an active protein phosphatase preferentially expressed in female gametocytes and ookinetes. Deletion of the endogenous ppkl gene caused abnormal ookinete development and differentiation, and dissociated apical microtubules from the inner-membrane complex, generating an immotile phenotype and failure to invade the mosquito mid-gut epithelium. These observations were substantiated by changes in localisation of cytoskeletal tubulin and actin, and the micronemal protein CTRP in the knockout mutant as assessed by indirect immunofluorescence. Finally, increased mRNA expression of dozi, a RNA helicase vital to zygote development was observed in ppkl(-) mutants, with global phosphorylation studies of ookinete differentiation from 1.5-24 h post-fertilisation indicating major changes in the first hours of zygote development. Our work demonstrates a stage-specific essentiality of the unique PPKL enzyme, which modulates parasite differentiation, motility and transmission.
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PMID:A unique protein phosphatase with kelch-like domains (PPKL) in Plasmodium modulates ookinete differentiation, motility and invasion. 2302 36

Signaling pathways controlled by reversible protein phosphorylation (catalyzed by kinases and phosphatases) in the malaria parasite Plasmodium are of great interest, for both increased understanding of parasite biology and identification of novel drug targets. Here, we report a functional analysis in Plasmodium of an ancient bacterial Shewanella-like protein phosphatase (SHLP1) found only in bacteria, fungi, protists, and plants. SHLP1 is abundant in asexual blood stages and expressed at all stages of the parasite life cycle. shlp1 deletion results in a reduction in ookinete (zygote) development, microneme formation, and complete ablation of oocyst formation, thereby blocking parasite transmission. This defect is carried by the female gamete and can be rescued by direct injection of mutant ookinetes into the mosquito hemocoel, where oocysts develop. This study emphasizes the varied functions of SHLP1 in Plasmodium ookinete biology and suggests that it could be a novel drug target for blocking parasite transmission.
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PMID:An ancient protein phosphatase, SHLP1, is critical to microneme development in Plasmodium ookinetes and parasite transmission. 2343 9


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