Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0024530 (malaria)
 44,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The induction mechanism of gamete formation (gametogenesis) in a rodent malaria parasite, Plasmodium berghei, was investigated using Ca2+ antagonists, protein kinase inhibitors and amiloride, an inhibitor of monovalent cation/H+ exchange. Treatment with 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8, a Ca2+ release inhibitor) and W-7/W-66 (calmodulin inhibitors) blocked formation of male gametes by inhibiting DNA synthesis from 1.5C to 8C level. In contrast, inhibitors of cAMP/cGMP-dependent protein kinases such as H-8, H-87, H-89 and staurosporine also ceased the development of gametocytes, but DNA synthesis in male gametocytes occurred as in the controls. Electron microscopy revealed that male gametocytes treated with TMB-8 and W-7 failed to enlarge nuclei and to form axonemes in the cytoplasm. In female gametocytes, treatment with both Ca2+ antagonists resulted in a dramatic morphological change in the endoplasmic reticulum (ER), which is thought to be a Ca2+ store. The ER network condensed near nuclei and was laminated by the abnormal attachment of ribosomes between two ER membranes. On the other hand, male gametocytes treated with protein kinase inhibitors or amiloride had enlarged nuclei and axonemes, but failed to develop further. The ER network in female gametocytes treated with these inhibitors was similar to that in the controls.
 ...
PMID:The roles of Ca2+/calmodulin- and cGMP-dependent pathways in gametogenesis of a rodent malaria parasite, Plasmodium berghei. 838 16

The heme oxygenase (HO) system was identified in the early 1970s as a distinct microsomal enzyme system that catalyzes formation of bile pigments (Maines and Kappas, 1974). Up to the early 1990s the system was considered only as a "molecular wrecking ball" (Lane, 1998) for degradation of the heme molecule and production of toxic waste products, CO and bile pigments. For those years, the HO system remained relatively unknown to the research community. In a rather short span of the past 10 years following the discovery of high levels of a second form of the enzyme, HO-2, in the brain, suggesting that "heme oxygenase in the brain has functions aside from heme degradation" (Sun et al., 1990); concomitant with finding that another toxic gas, NO, is a signal molecule for generation of cGMP (Ignarro et al., 1982), the system was propelled into main stream research. This propulsion was fueled by the realization of the multiple and diverse functions of heme degradation products. Heme oxygenase has now found relevance in all kinds of human pathophysiology ranging from stroke, cancer, multiple sclerosis, and malaria to transplantation and immune response. As it turns out, its potential benefits are mesmerizing investigators in diverse fields (Lane, 1998). The most recent findings with HO-2 being a hemoprotein and potentially an intracellular "sink" for NO (McCoubrey et al., 1997a; Ding et al., 1999), together with the discovery of the third form of the enzyme, HO-3 (McCoubrey et al., 1997b), are likely to insure the widespread interest in the enzyme system in the coming years. The present review is intended to highlight molecular properties of HO isozymes and their likely functions in the brain. Extended reviews of the system are found in Maines (1992, 1997).
 ...
PMID:The heme oxygenase system and its functions in the brain. 1087 44

Sex is an obligate step in the life cycle of the malaria parasite and occurs in the midgut of the mosquito vector. With both Plasmodium falciparum and Plasmodium berghei, the tryptophan metabolite xanthurenic acid induces the release of motile male gametes from red blood cells (exflagellation), a prerequisite for fertilization. The addition of cGMP or phosphodiesterase inhibitors to cultures of mature gametocytes has also been shown to stimulate exflagellation. Here, we demonstrate that there is a guanylyl cyclase activity associated with mature P. falciparum gametocyte membrane preparations, which is dependent on the presence of Mg(2+)/Mn(2+) but is inhibited by Ca(2+). Significantly, this activity is increased on addition of xanthurenic acid. In contrast, a xanthurenic acid precursor (3-hydroxykynurenine), which is not an inducer of exflagellation, does not induce this guanylyl cyclase activity. These results therefore suggest that xanthurenic acid-induced exflagellation may be mediated by activation of the parasite cGMP signalling pathway.
 ...
PMID:The gametocyte-activating factor xanthurenic acid stimulates an increase in membrane-associated guanylyl cyclase activity in the human malaria parasite Plasmodium falciparum. 1170 75

Cyclic GMP-dependent protein kinases (PKGs) are the major mediators of the cGMP signal transduction pathway and regulate a variety of physiological effects. We report here the characterization of an unusual PKG from the human malaria parasite Plasmodium falciparum (designated PfPKG). The 97.5 kDa protein contains some of the structural features of mammalian PKGs but, uniquely, contains a third predicted cGMP binding site and a degenerate fourth. Using both protein kinase activity assays and Western blotting with native P. falciparum proteins, we demonstrate here that PfPKG is expressed predominantly in the ring stage of the life cycle, suggesting a role in the development of asexual blood stage parasites. An Escherichia coli-derived recombinant protein (PfPKG2, Met115-Phe853) was purified and shown to have phosphotransferase activity in terms of both substrate phosphorylation and auto-phosphorylation. This activity was stimulated at least fivefold by 1.0 microM cyclic GMP, but was not stimulated by cAMP or by 8-pCPT-cGMP, which is a potent activator of mammalian PKGs. Several protein kinase inhibitors exhibited a range of inhibitory effects on PfPKG activity. Biochemical analysis therefore shows that PfPKG is distinct from mammalian PKGs with respect to both cyclic nucleotide analogue activation and inhibition profiles.
 ...
PMID:A novel cyclic GMP-dependent protein kinase is expressed in the ring stage of the Plasmodium falciparum life cycle. 1206 3

This is the first report of molecular characterization of a novel cyclic nucleotide PDE (phosphodiesterase), isolated from the human malaria parasite Plasmodium falciparum and designated PfPDE1. PfPDE1 cDNA encodes an 884-amino-acid protein, including six putative transmembrane domains in the N-terminus followed by a catalytic domain. The PfPDE1 gene is a single-copy gene consisting of two exons and a 170 bp intron. PfPDE1 transcripts were abundant in the ring form of the asexual blood stages of the parasite. The C-terminal catalytic domain of PfPDE1, produced in Escherichia coli, specifically hydrolysed cGMP with a K(m) value of 0.65 microM. Among the PDE inhibitors tested, a PDE5 inhibitor, zaprinast, was the most effective, having an IC50 value of 3.8 microM. The non-specific PDE inhibitors IBMX (3-isobutyl-1-methylxanthine), theophylline and the antimalarial chloroquine had IC50 values of over 100 microM. Membrane fractions prepared from P. falciparum at mixed asexual blood stages showed potent cGMP hydrolytic activity compared with cytosolic fractions. This hydrolytic activity was sensitive to zaprinast with an IC50 value of 4.1 microM, but insensitive to IBMX and theophylline. Furthermore, an in vitro antimalarial activity assay demonstrated that zaprinast inhibited the growth of the asexual blood parasites, with an ED50 value of 35 microM. The impact of cyclic nucleotide signalling on the cellular development of this parasite has previously been discussed. Thus this enzyme is suggested to be a novel potential target for the treatment of the disease malaria.
 ...
PMID:PfPDE1, a novel cGMP-specific phosphodiesterase from the human malaria parasite Plasmodium falciparum. 1603 15

Mosquito natriuretic peptide (MNP), an uncharacterised peptide from the yellow fever mosquito, Aedes aegypti, acts via cyclic AMP to stimulate secretion of Na+-rich urine by opening a Na+ conductance in the basolateral membrane of Malpighian tubule principal cells. Corticotropin releasing factor (CRF)-related peptides and calcitonin (CT)-like diuretic peptides use cyclic AMP as a second messenger and were therefore considered likely candidates for MNP. BLAST searches of the genome of the malaria mosquito Anopheles gambiae, gave sequences for the CRF-related peptide Anoga-DH44 and the CT-like peptide Anoga-DH31, which were synthesised and tested for effects on Malpighian tubules from An. gambiae and Ae. aegypti, together with 8-bromo-cyclic AMP. The cyclic AMP analogue stimulated secretion of Na+-rich urine by An. gambiae Malpighian tubules, reproducing the response to MNP in Ae. aegypti. It also depolarised the principal cell basolateral membrane voltage (Vb) while hyperpolarising the transepithelial voltage (Vt) to a similar extent. Anoga-DH4) and Anoga-DH31 stimulated production of cyclic AMP, but not cyclic GMP, by Malpighian tubules of An. gambiae. Both peptides had diuretic activity, but only Anoga-DH31 had natriuretic activity and stimulated fluid secretion to the same extent as 8-bromo-cyclic AMP. Likewise, Anoga-DH31 reproduced the effects of cyclic AMP on tubule electrophysiology, whereas Anoga-DH44 initially hyperpolarised Vb and depolarised Vt, which is the opposite of the effect of Anoga-DH31. Anoga-DH44 and Anoga-DH31 were also tested for effects on fluid secretion and ion transport by Ae. aegypti tubules. As in An. gambiae, the CRF-related peptide Anoga-DH44 had a non-specific effect on the transport of Na+ and K+, whereas the CT-like peptide Anoga-DH31 specifically stimulated transepithelial Na+ transport. We conclude that the CT-like peptide Anoga-DH31 is the previously uncharacterised mosquito natriuretic peptide.
 ...
PMID:Mosquito natriuretic peptide identified as a calcitonin-like diuretic hormone in Anopheles gambiae (Giles). 1610 90

Malaria kills over 3,000 children each day. Modern molecular and biochemical approaches are being used to help understand and control Plasmodium falciparum, the parasite that causes this deadly disease. New drugs are being invented for both chemoprophylaxis and therapeutic treatments and their use is discussed along side that of the more commonly used treatments. Classical genetic crosses coupled with molecular analysis of gene loci are use to explain the genetics behind the development of specific drug resistances that the parasites have naturally developed. Rapid advances in DNA sequencing techniques have allowed the compete sequencing of the P. falciparum and several other rodent malaria parasite genomes. Proteomics and computational analysis of these vast databanks are being used to model and investigate the three-dimensional structure of many key malaria proteins in an attempt to facilitate drug design. Recombinant protein expression in bacteria and yeast coupled with cGMP purification technologies and conditions have lead to the recent availability of several dozen malaria protein antigens for human-use Phase I and Phase II vaccine trials. Drug companies, private foundations, and key government agencies have contributed to the coordinated efforts needed to test these antigens, adjuvants and delivery methods in an effort to find an effective malaria vaccine that will prevent infection and disease.
 ...
PMID:Malaria: therapy, genes and vaccines. 1671 77

The 42 kDa cleavage product from the carboxyl end of the Plasmodium falciparum merozoite surface protein 1 (MSP1(42)) is an important blood-stage malaria vaccine target. Several recombinant protein expression systems have been used for production of MSP1(42) including yeast (Saccharomyces cerevisiae and Pichia pastoris), Escherichia coli, baculovirus and transgenic animals. To date, all of the reported recombinant proteins include a 6 x His affinity tag to facilitate purification, including three MSP1(42) clinical grade proteins currently in human trials. Under some circumstances, the presence of the 6 x His tag may not be desirable. Therefore, we were interested to produce clinical grade MSP1(42) without a 6 x His affinity tag from E. coli inclusion bodies. We produced a recombinant MSP1(42) with a P. falciparum FUP (Uganda-Palo Alto) phenotype which accounts for a substantial proportion of the MSP1(42) protein observed in African isolates. EcMSP1(42)-FUP was produced in E. coli inclusion bodies by high cell mass induction with IPTG using 5 L and 60 L bioreactors. Isolated inclusion bodies were solubilized in 8M guanidine-HCl and the EcMSP1(42)-FUP protein refolded by rapid dilution. Refolded EcMSP1(42)-FUP was purified using hydrophobic interaction chromatography, anion exchange chromatography, and size exclusion chromatography, and subject to biochemical characterization for integrity, identity, and purity. Endotoxin and host cell protein levels were within acceptable limits for human use. The process was successfully transferred to pilot-scale production in a cGMP environment. A final recovery of 87.8 mg of clinical-grade material per liter of fermentation broth was achieved. The EcMSP1(42)-FUP clinical antigen is available for preclinical evaluation and human studies.
 ...
PMID:Production and characterization of clinical grade Escherichia coli derived Plasmodium falciparum 42 kDa merozoite surface protein 1 (MSP1(42)) in the absence of an affinity tag. 1688 20

Phosphodiesterase (PDE) and guanylyl cyclase (GC) enzymes are key components of the cGMP signalling pathway and are encoded in the genome of Plasmodium falciparum. Here we investigate the role of specific GC and PDE isoforms in gamete formation--a process that is essential for malaria transmission and occurs in the Anopheles mosquito midgut following feeding on an infected individual. Details of the intracellular signalling events controlling development of the male and female gametes from their precursors (gametocytes) remain sparse in P. falciparum. Previous work involving the addition of pharmacological agents to gametocytes implicated cGMP in exflagellation--the emergence of highly motile, flagellated male gametes from the host red blood cell. In this study we show that decreased GC activity in parasites having undergone disruption of the PfGCbeta gene had no significant effect on gametogenesis. By contrast, decreased cGMP-PDE activity during gametocyte development owing to disruption of the PfPDEdelta gene, led to a severely reduced ability to undergo gametogenesis. This suggests that the concentration of cGMP must be maintained below a threshold in the developing gametocyte to allow subsequent differentiation to proceed normally. The data indicate that PfPDEdelta plays a crucial role in regulating cGMP levels during sexual development.
 ...
PMID:Disruption of a Plasmodium falciparum cyclic nucleotide phosphodiesterase gene causes aberrant gametogenesis. 1845 84

Malaria parasite transmission requires differentiation of male and female gametocytes into gametes within a mosquito following a blood meal. A mosquito-derived molecule, xanthurenic acid (XA), can trigger gametogenesis, but the signalling events controlling this process in the human malaria parasite Plasmodium falciparum remain unknown. A role for cGMP was revealed by our observation that zaprinast (an inhibitor of phosphodiesterases that hydrolyse cGMP) stimulates gametogenesis in the absence of XA. Using cGMP-dependent protein kinase (PKG) inhibitors in conjunction with transgenic parasites expressing an inhibitor-insensitive mutant PKG enzyme, we demonstrate that PKG is essential for XA- and zaprinast-induced gametogenesis. Furthermore, we show that intracellular calcium (Ca2+) is required for differentiation and acts downstream of or in parallel with PKG activation. This work defines a key role for PKG in gametogenesis, elucidates the hierarchy of signalling events governing this process in P. falciparum, and demonstrates the feasibility of selective inhibition of a crucial regulator of the malaria parasite life cycle.
 ...
PMID:Gametogenesis in malaria parasites is mediated by the cGMP-dependent protein kinase. 1853 80


1 2 3 4 Next >>