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)

Chloroquine is a potent lysomotropic therapeutic agent used in the treatment of malaria. The mechanism of the chloroquine-mediated modulation of new cardiolipin biosynthesis in isolated rat liver hepatocytes and H9c2 cardiac myoblast cells was addressed in this study. Hepatocytes or H9c2 cells were incubated with [1,3-(3)H]glycerol in the absence or presence of chloroquine and cardiolipin biosynthesis was examined. The presence of chloroquine in the incubation medium of hepatocytes resulted in a rapid accumulation of radioactivity in cardiolipin indicating an elevated de novo biosynthesis. In contrast, chloroquine caused a reduction in radioactivity incorporated into cardiolipin in H9c2 cells. The presence of brefeldin A, colchicine or 3-methyladenine did not effect radioactivity incorporated into cardiolipin nor the chloroquine-mediated stimulation of cardiolipin biosynthesis in hepatocytes indicating that vesicular transport, cytoskeletal elements or increased autophagy were not involved in de novo cardiolipin biosynthesis induced by chloroquine. The addition of chloroquine to isolated rat liver membrane fractions did not affect the activity of the enzymes of de novo cardiolipin biosynthesis but resulted in an inhibition of mitochondrial cytidine-5'-diphosphate-1,2-diacyl-sn-glycerol hydrolase activity. The mechanism for the reduction in cardiolipin biosynthesis in H9c2 cells was a chloroquine-mediated inhibition of glycerol uptake and this did not involve impairment of lysosomal function. The kinetics of the chloroquine-mediated inhibition of glycerol uptake indicated the presence of a glycerol transporter in H9c2 cells. The results of this study clearly indicate that chloroquine has markedly different effects on glycerol uptake and cardiolipin biosynthesis in hepatocytes and H9c2 cardiac cells.
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PMID:Differential effects of chloroquine on cardiolipin biosynthesis in hepatocytes and H9c2 cardiac cells. 1088 36

Cytidine diphosphate-diacylglycerol (CDP-DAG), an obligatory intermediate compound in the biosynthesis of the major anionic and zwitterionic phospholipids, is synthesized by CDP-DAG synthase (CDS). The gene encoding CDS was isolated from the human malaria parasite Plasmodium falciparum, based on sequence conservation to CDS from other organisms. The P. falciparum gene is located as a single copy on chromosome 14. The open reading frame (ORF) of PfCDS gene encodes a putative protein of 667 amino acids and 78 kDa. Only the C-terminal 422 amino acids share 40% homology with eukaryotic CDSs. The very long and non-conserved N-terminal region of 245 amino acids is hydrophilic and contains asparagine-rich and repetitive sequences. Two mRNA of 3.5 and 4 kb were detected. Transcription is developmentally regulated during the asexual intraerythrocytic cycle, being the weakest in the ring-stage. PfCDS enzyme activities in infected erythrocytes correlates with the transcription pattern, consistent with an increased synthesis of phospholipids in trophozoites and schizonts. Antisera raised against two synthetic peptides from the C-terminal region of PfCDS detected a single protein of 51 kDa in Western blot analysis, specific for parasitized erythrocytes. A protein of 28 kDa was recognized by an antiserum against an N-terminal peptide, indicating that PfCDS is proteolytically processed. Expression of 51- and 28-kDa proteins was developmentally regulated similar to regulation of the transcripts and the enzyme activity. The conserved C-terminal region of PfCDS, cloned into a eukaryote expression vector and transfected in COS-7 cells, showed a two-fold increase CDP-DAG synthase activities, indicating that the isolated gene most likely encoded the P. falciparum CDS enzyme.
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PMID:Characterization of Plasmodium falciparum CDP-diacylglycerol synthase, a proteolytically cleaved enzyme. 1098 48

The YgbP protein of Escherichia coli encodes the enzyme 4-diphosphocytidyl-2-C-methylerythritol (CDP-ME) synthetase, a member of the cytidyltransferase family of enzymes. CDP-ME is an intermediate in the mevalonate-independent pathway for isoprenoid biosynthesis in a number of prokaryotic organisms, algae, the plant plastids and the malaria parasite. Because vertebrates synthesize isoprenoid precursors using a mevalonate pathway, CDP-ME synthetase and other enzymes of the mevalonate-independent pathway for isoprenoid production represent attractive targets for the structure-based design of selective antibacterial, herbicidal and antimalarial drugs. The high-resolution structures of E. coli CDP-ME synthetase in the apo form and complexed with both CTP-Mg2+ and CDP-ME-Mg2+ reveal the stereochemical principles underlying both substrate and product recognition as well as catalysis in CDP-ME synthetase. Moreover, these complexes represent the first experimental structures for any cytidyltransferase with both substrates and products bound.
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PMID:Structure of 4-diphosphocytidyl-2-C- methylerythritol synthetase involved in mevalonate- independent isoprenoid biosynthesis. 1142 97

Higher plants, several algae, bacteria, some strains of Streptomyces and possibly malaria parasite Plasmodium falciparum contain the novel, plastidic DOXP/MEP pathway for isoprenoid biosynthesis. This pathway, alternative with respect to the classical mevalonate pathway, starts with condensation of pyruvate and glyceraldehyde-3-phosphate which yields 1-deoxy-D-xylulose 5-phosphate (DOXP); the latter product can be converted to isopentenyl diphosphate (IPP) and eventually to isoprenoids or thiamine and pyridoxal. Subsequent reactions of this pathway involve transformation of DOXP to 2-C-methyl-D-erythritol 4-phosphate (MEP) which after condensation with CTP forms 4-diphosphocytidyl-2-amethyl-D-erythritol (CDP-ME). Then CDP-ME is phosphorylated to 4-diphosphocytidyl-2-amethyl-D-erythritol 2-phosphate (CDP-ME2P) and to 2-C-methyl-D-erythritol-2,4-cyclodiphosphate (ME-2,4cPP) which is the last known intermediate of the DOXP/MEP pathway. For- mation of IPP and dimethylallyl diphosphate (DMAPP) from ME-2,4cPP still requires clarification. This novel pathway appears to be involved in biosynthesis of carotenoids, phytol (side chain of chlorophylls), isoprene, mono-, di-, tetraterpenes and plastoquinone whereas the mevalonate pathway is responsible for formation of sterols, sesquiterpenes and triterpenes. Several isoprenoids were found to be of mixed origin suggesting that some exchange and/or cooperation exists between these two pathways of different biosynthetic origin. Contradictory results described below could indicate that these two pathways are operating under different physiological conditions of the cell and are dependent on the developmental state of plastids.
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PMID:Isoprenoid biosynthesis via 1-deoxy-D-xylulose 5-phosphate/2-C-methyl-D-erythritol 4-phosphate (DOXP/MEP) pathway. 1183 75

Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) are the main membrane phospholipids (PLs) of Plasmodium parasites and can be generated by the de novo (Kennedy) CDP-choline and CDP-ethanolamine pathways and by the CDP-diacylglycerol dependent pathway. The Kennedy pathways initiate from exogenous choline and ethanolamine involving choline kinase (CK) and ethanolamine kinase (EK), followed by the choline-phosphate cytidylyltransferase (CCT) and ethanolamine-phosphate cytidylyltransferase (ECT) that catalyse the formation of CDP-choline and CDP-ethanolamine. Finally, in Plasmodium, PC and PE are apparently synthesized by a common choline/ethanolamine-phosphotransferase (CEPT). Here, we have studied the essential nature of the Kennedy pathways in Plasmodium berghei, a rodent malaria parasite. Sequence analysis of the P. berghei CEPT, CCT, ECT and CK enzymes revealed the presence of all catalytic domains and essential residues and motifs necessary for enzymatic activities. Constructs were designed for the generation of gene knockout and GFP-fusions of the cept, cct, ect and ck genes in P. berghei. We found that all four genes were consistently refractory to knockout attempts. At the same time, successful tagging of these proteins with GFP demonstrated that the loci were targetable and indicated that these genes are essential in P. berghei blood stage parasites. GFP-fusions of CCT, ECT and CK were found in the cytosol whereas the GFP-CEPT mainly localised in the endoplasmic reticulum. These results indicate that both CDP-choline and CDP-ethanolamine de novo pathways are essential for asexual P. berghei development and are non-redundant with other possible sources of PC and PE.
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PMID:The Kennedy phospholipid biosynthesis pathways are refractory to genetic disruption in Plasmodium berghei and therefore appear essential in blood stages. 2047 40

Throughout the Plasmodium life cycle, malaria parasites repeatedly undergo rapid cellular growth and prolific divisions, necessitating intense membrane neogenesis and, in particular, the acquisition of high amounts of phospholipids. At the intraerythrocytic stage, glycerophospholipids are the main parasite membrane constituents, which mostly originate from the Plasmodium-encoded enzymatic machinery. Several proteins and entire pathways have been characterized and their features reported, thereby generating a global view of glycerophospholipid synthesis across Plasmodium spp. The malaria parasite displays a panoply of pathways that are seldom found together in a single organism. The major glycerophospholipids are synthesized via ancestral prokaryotic CDP-diacylglycerol-dependent pathways and eukaryotic-type de novo pathways. The parasite exhibits additional reactions that bridge some of these routes and are otherwise restricted to some organisms, such as plants, while base-exchange mechanisms are largely unexplored in Plasmodium. Marked differences between Plasmodium spp. have also been reported in phosphatidylcholine and phosphatidylethanolamine synthesis. Little is currently known about glycerophospholipid acquisition at non-erythrocytic stages, but recent data reveal that intrahepatocytic parasites, oocysts and sporozoites import various host lipids, and that de novo fatty acid synthesis is only crucial at the late liver stage. More studies on the different Plasmodium developmental stages are needed, to further assemble the different pieces of this glycerophospholipid synthesis puzzle, which contains highly promising therapeutic targets.
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PMID:Glycerophospholipid acquisition in Plasmodium - a puzzling assembly of biosynthetic pathways. 2060 72

The intra-erythrocytic proliferation of the human malaria parasite Plasmodium falciparum requires massive synthesis of PE (phosphatidylethanolamine) that together with phosphatidylcholine constitute the bulk of the malaria membrane lipids. PE is mainly synthesized de novo by the CDP:ethanolamine-dependent Kennedy pathway. We previously showed that inhibition of PE biosynthesis led to parasite death. In the present study we characterized PfECT [P. falciparum CTP:phosphoethanolamine CT (cytidylyltransferase)], which we identified as the rate-limiting step of the PE metabolic pathway in the parasite. The cellular localization and expression of PfECT along the parasite life cycle were studied using polyclonal antibodies. Biochemical analyses showed that the enzyme activity follows Michaelis-Menten kinetics. PfECT is composed of two CT domains separated by a linker region. Activity assays on recombinant enzymes upon site-directed mutagenesis revealed that the N-terminal CT domain was the only catalytically active domain of PfECT. Concordantly, three-dimensional homology modelling of PfECT showed critical amino acid differences between the substrate-binding sites of the two CT domains. PfECT was predicted to fold as an intramolecular dimer suggesting that the inactive C-terminal domain is important for dimer stabilization. Given the absence of PE synthesis in red blood cells, PfECT represents a potential antimalarial target opening the way for a rational conception of bioactive compounds.
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PMID:Biochemical characterization of Plasmodium falciparum CTP:phosphoethanolamine cytidylyltransferase shows that only one of the two cytidylyltransferase domains is active. 2319 4