Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “PLASMODIUM”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 451 records · Page 25Linked to original sources
PubMed1986

Purification and characterization of Plasmodium berghei DNA topoisomerases I and II: drug action, inhibition of decatenation and relaxation, and stimulation of DNA cleavage.

It has recently been suggested that topoisomerases could be important targets for drugs used in several diseases. This prompted us to purify and characterize the topoisomerases I and II present in the erythrocytes of protozoan parasites of the genus Plasmodium, the causative agent of malaria, in order to later use these enzymatic systems in antimalarial drug assays. The topoisomerases were purified from Plasmodium berghei, a parasite of mouse red cells. The Plasmodium topoisomerase II consists of two subunits with a molecular weight of about 160K. The enzyme is ATP- and Mg2+-dependent. The conditions for the reactions of relaxation, unknotting, decatenation, and catenation were found to be similar to those observed with enzymes from other eukaryotic cells. The Plasmodium topoisomerase I is a monomeric enzyme with a Mr of 70K-100K. It is ATP-independent and K+- or Na-dependent. Mg2+ is not required for relaxation but stimulates the reaction. Topoisomerase II was more sensitive to drug action than topoisomerase I. The most active drugs were the ellipticine derivatives. The antimalarial drugs, currently used in human clinical therapy, were poor inhibitors. Some antitumoral drugs stimulated the double-stranded DNA cleavage activity of Plasmodium topoisomerase II, like that of mammalian topoisomerases II. Antimalarial drugs had no stimulating activity. It is therefore suggested that Plasmodium topoisomerases are not good targets for antimalarial drugs.

Alkaloids↗
PubMed2005

The Plasmodium protein network diverges from those of other eukaryotes.

Plasmodium falciparum is the pathogen responsible for over 90% of human deaths from malaria. Therefore, it has been the focus of a considerable research initiative, involving the complete DNA sequencing of the genome, large-scale expression analyses, and protein characterization of its life-cycle stages. The Plasmodium genome sequence is relatively distant from those of most other eukaryotes, with more than 60% of the 5,334 encoded proteins lacking any notable sequence similarity to other organisms. To systematically elucidate functional relationships among these proteins, a large two-hybrid study has recently mapped a network of 2,846 interactions involving 1,312 proteins within Plasmodium. This network adds to a growing collection of available interaction maps for a number of different organisms, and raises questions about whether the divergence of Plasmodium at the sequence level is reflected in the configuration of its protein network. Here we examine the degree of conservation between the Plasmodium protein network and those of model organisms. Although we find 29 highly connected protein complexes specific to the network of the pathogen, we find very little conservation with complexes observed in other organisms (three in yeast, none in the others). Overall, the patterns of protein interaction in Plasmodium, like its genome sequence, set it apart from other species.

Animals↗
PubMed2006

New approach for high-throughput screening of drug activity on Plasmodium liver stages.

Plasmodium liver stages represent potential targets for antimalarial prophylactic drugs. Nevertheless, there is a lack of molecules active on these stages. We have now developed a new approach for the high-throughput screening of drug activity on Plasmodium liver stages in vitro, based on an infrared fluorescence scanning system. This method allowed us to count automatically and rapidly Plasmodium-infected hepatocytes, using different hepatic cells and different Plasmodium species, including Plasmodium falciparum. This new technique is well adapted for high-throughput drug screening and should facilitate the identification of new antimalarial compounds active on Plasmodium liver stages.

Animals↗
PubMed2006

Two Plasmodium rhomboid proteases preferentially cleave different adhesins implicated in all invasive stages of malaria.

Invasion of host cells by the malaria pathogen Plasmodium relies on parasite transmembrane adhesins that engage host-cell receptors. Adhesins must be released by cleavage before the parasite can enter the cell, but the processing enzymes have remained elusive. Recent work indicates that the Toxoplasma rhomboid intramembrane protease TgROM5 catalyzes this essential cleavage. However, Plasmodium does not encode a direct TgROM5 homolog. We examined processing of the 14 Plasmodium falciparum adhesins currently thought to be involved in invasion by both model and Plasmodium rhomboid proteases in a heterologous assay. While most adhesins contain aromatic transmembrane residues and could not be cleaved by nonparasite rhomboid proteins, including Drosophila Rhomboid-1, Plasmodium falciparum rhomboid protein (PfROM)4 (PFE0340c) was able to process these adhesins efficiently and displayed novel substrate specificity. Conversely, PfROM1 (PF11_0150) shared specificity with rhomboid proteases from other organisms and was the only PfROM able to cleave apical membrane antigen 1 (AMA1). PfROM 1 and/or 4 was thus able to cleave diverse adhesins including TRAP, CTRP, MTRAP, PFF0800c, EBA-175, BAEBL, JESEBL, MAEBL, AMA1, Rh1, Rh2a, Rh2b, and Rh4, but not PTRAMP, and cleavage relied on the adhesin transmembrane domains. Swapping transmembrane regions between BAEBL and AMA1 switched the relative preferences of PfROMs 1 and 4 for these two substrates. Our analysis indicates that PfROMs 1 and 4 function with different substrate specificities that together constitute the specificity of TgROM5 to cleave diverse adhesins. This is the first enzymatic analysis of Plasmodium rhomboid proteases and suggests an involvement of PfROMs in all invasive stages of the malaria lifecycle, in both the vertebrate host and the mosquito vector.

Animals↗
PubMed2004

Natural Plasmodium infections in Anopheles darlingi and Anopheles benarrochi (Diptera: Culicidae) from eastern Peru.

Malaria, both Plasmodium falciparum (Welch) and Plasmodium vivax (Grassi & Feletti), has reemerged as a significant public health disease issue in Peru, especially in forested areas in the eastern part of the country. The spread of Anopheles darlingi Root, the principal South American malaria vector, into new areas of Peru is thought to be a factor in this resurgence. However, epidemiological evidence suggests that in malaria endemic areas of eastern Peru where An. darlingi does not occur, other species are involved in malaria transmission. The objective of this study was to analyze Anopheles species collected from 11 provinces within four departments in eastern Peru during 2001 and 2002 for infections with P. falciparum and P. vivax. More than 84,000 Anopheles mosquitoes representing 13 species were tested by enzyme-linked immunosorbent assay for the presence of Plasmodium circumsporozoite (CS) proteins. Of these, only An. darlingi and Anopheles benarrochi Gabaldón, Cova García & López were found positive. In total, 14 (0.98%) of 1,432 pools of An. darlingi were positive for Plasmodium species; specifically 10 (0.70%) pools were positive for P. falciparum, two (0.14%) were positive for P. vivax VK210, and two (0.14%) were positive for P. vivax VK247 proteins. Nine (0.14%) of 6,323 pools of An. benarrochi were positive for Plasmodium; five (0.08%) of 6,323 pools were positive for P. falciparum, two (0.03%) were positive for P. vivax VK247, one (0.02%) was positive for mixed P. vivax VK210/VK247 infections, and one (0.02%) was positive for mixed P. falciparum and P. vivax VK210 CS-proteins. Although infection rates in An. benarrochi were significantly lower (0.14%) than rates found for An. darlingi (0.98%), our data suggest that An. benarrochi may play a role in transmitting and maintaining Plasmodium species in various malaria endemic areas of eastern Peru.

Animals↗
PubMed2003

The development of exoerythrocytic stages of Plasmodium inui shortti in New World monkeys.

Attempts are being made to adapt Old World monkey malarial parasites to New World monkeys for vaccine and molecular studies. Several of these (Plasmodium cynomolgi Berok, Plasmodium fragile, and Plasmodium knowlesi) grow readily but have failed to produce infective gametocytes. Plasmodium gonderi and Plasmodium fieldi develop in the liver after sporozoite inoculation but have failed to establish infection in the erythrocyte. Anopheles dirus mosquitoes infected with Plasmodium inui shortti by feeding on infected macaques transmitted the infection to Saimiri boliviensis monkeys. Infective gametocytes were produced, and sporozoite transmission from Saimiri to Saimiri monkey was obtained. Exoerythrocytic stages have also been observed in the liver tissue of Saimiri monkeys. The availability of the complete transmission cycle provides an additional resource for immunologic and vaccine studies.

Animals↗
PubMed2005

[Preparation of a monoclonal antibodies against Plasmodium falciparum glutamate dehydrogenase and establishment of colloidal gold-immunochromatographic assay].

OBJECTIVE: To prepare a monoclonal antibodies (mAbs) against glutamate dehydrogenase (GDH) of Plasmodium falciparum (FCC1/HN strain) and establish colloidal gold-immunochromatographic assay (GICA) for diagnosis of Plasmodium falciparum malaria. METHODS: Recombinant GDH was used to immunize Balb/C mice and the mAbs against GDH were prepared using hybridoma technique followed by identification of IgG isotype and its affinity. Protein-G affinity chromatography was employed to purify the antibodies, which were labeled with colloidal gold for establishment of GICA for Plasmodium falciparum detection. RESULTS: Six mAbs were obtained and identified as IgG1(kappa) of IgG isotypes with affinity constants (Kaff) ranging from 1 x 10(-8) to 2.8 x 10(-10). GICA had a sensitivity of 86.66%; and specificity of 96.43%; for Plasmodium falciparum detection compared with routine microscopic examination. CONCLUSION: The established GICA is rapid and accurate for Plasmodium falciparum detection with such potential utility as for instant diagnosis of Plasmodium falciparum malaria.

Animals↗
PubMed1990

Plasmodium yoelii nigeriensis circumsporozoite gene structure and its implications for the evolution of the repeat regions.

The circumsporozoite (CS) gene encodes the most immunogenic component of the plasmodial sporozoites. The immunodominant epitope-encoding domain of the CS gene shows sequences that are repeated in tandem. A detailed analysis of the CS repeats of certain closely related malaria parasites (strains of Plasmodium cynomolgi, Plasmodium knowlesi, and Plasmodium vivax) showed that they evolve rapidly yet are well conserved within the gene. We were interested in studying whether the CS repeats of Plasmodia more distantly related to these species evolve in a similar manner. To this end, we isolated and characterized the Plasmodium yoelii nigeriensis CS gene. A comparative analysis of its sequence with that of Plasmodium yoelii yoelii shows that both have three sets of repeats, termed PR, R1, and R2. The R1 and basically also the R2 sequences show the features observed in most CS repeats, i.e., they evolve rapidly and are nearly perfectly tandemly repeated. In contrast, the PR repeats are not internally conserved nor divergent in sequence. The implications of these findings for the evolution of the CS repeats are discussed.

Amino Acid Sequence↗
PubMed2004

Proteomic approaches to studying drug targets and resistance in Plasmodium.

Ever increasing drug resistance by Plasmodium falciparum, the most virulent of human malaria parasites, is creating new challenges in malaria chemotherapy. The entire genome sequences of P. falciparum and the rodent malaria parasite, P. yoelii yoelii are now available. Extensive genome sequence data from other Plasmodium species including another important human malaria parasite, P. vivax are also available. Powerful research techniques coupled to genomic resources are needed to help identify new drug and vaccine targets against malaria. Applied to Plasmodium, proteomics combines high-resolution protein or peptide separation with mass spectrometry and computer software to rapidly identify large numbers of proteins expressed from various stages of parasite development. Proteomic methods can be applied to study sub-cellular localization, cell function, organelle composition, changes in protein expression patterns in response to drug exposure, drug-protein binding and validation of data from genomic annotation and transcript expression studies. Recent high-throughput proteomic approaches have provided a wealth of protein expression data on P. falciparum, while smaller-scale studies examining specific drug-related hypotheses are also appearing. Of particular interest is the study of mechanisms of action and resistance of drugs such as the quinolines, whose targets currently may not be predictable from genomic data. Coupling the Plasmodium sequence data with bioinformatics, proteomics and RNA transcript expression profiling opens unprecedented opportunities for exploring new malaria control strategies. This review will focus on pharmacological research in malaria and other intracellular parasites using proteomic techniques, emphasizing resources and strategies available for Plasmodium.

Animals↗
PubMedDate not supplied

Plasmodium immobilization of Physarella oblonga (Berk. & Curt.) Morgan (Myxomycetes) using kaolinite as a matrix of entrapment.

The possibility of using kaolinite-immobilized plasmodium fragments of Physarella oblonga (Berk. & Curt.) Morgan to maintain their metabolic activity was examined. The immobilization process was carried out with 1 mg of plasmodium of P. oblonga entrapped in 10 g of kaolinite. Sodium acetate (1 mM) was used as a metabolic precursor. The collection of fractions was carried out during a one month period, and extracted with ether/ethyl acetate and chloroform/acetonitrile. The extractions from plasmodium in natura were accomplished with the same solvents. The extracts obtained were analyzed in a spectrophotometer at 266 nm and 310 nm, and by thin layer chromatography to assess the productivity of the immobilized plasmodium. The absorbances of the extracts in both wavelengths and the chromatographic tests showed the synthesis of compounds by the immobilized material. Three chromatographic spots were observed in the extracts obtained from the immobilized plasmodium. Two spots coincided with the R(f) values and coloration of the spots observed for the material in natura used as a reference. The kaolinite-immobilized plasmodium of P. oblonga can remain metabolically active for at least one month at room temperature and ambient light conditions.

Kaolin↗
PubMed2004

A member of a conserved Plasmodium protein family with membrane-attack complex/perforin (MACPF)-like domains localizes to the micronemes of sporozoites.

Pore-forming proteins are employed by many pathogens to achieve successful host colonization. Intracellular pathogens use pore-forming proteins to invade host cells, survive within and productively interact with host cells, and finally egress from host cells to infect new ones. The malaria-causing parasites of the genus Plasmodium evolved a number of life cycle stages that enter and replicate in distinct cell types within the mosquito vector and vertebrate host. Despite the fact that interaction with host-cell membranes is a central theme in the Plasmodium life cycle, little is known about parasite proteins that mediate such interactions. We identified a family of five related genes in the genome of the rodent malaria parasite Plasmodium yoelii encoding secreted proteins all bearing a single membrane-attack complex/perforin (MACPF)-like domain. Each protein is highly conserved among Plasmodium species. Gene expression analysis in P. yoelii and the human malaria parasite Plasmodium falciparum indicated that the family is not expressed in the parasites blood stages. However, one of the genes was significantly expressed in P. yoelii sporozoites, the stage transmitted by mosquito bite. The protein localized to the micronemes of sporozoites, organelles of the secretory invasion apparatus intimately involved in host-cell infection. MACPF-like proteins may play important roles in parasite interactions with the mosquito vector and transmission to the vertebrate host.

Amino Acid Motifs↗
PubMed2001

von Willebrand Factor A domain-related protein, a novel microneme protein of the malaria ookinete highly conserved throughout Plasmodium parasites.

The mosquito-invasive form of the malarial parasite, the ookinete, develops numerous secretory organelles, called micronemes, in the apical cytoplasm. Micronemal proteins are thought to be secreted during midgut invasion and to play a crucial role in attachment and motility of the ookinete. We found a novel ookinete micronemal protein of rodent malarial parasite Plasmodium berghei, named P. berghei von Willebrand factor A domain-related protein (PbWARP), and report it here as a putative soluble adhesive protein of the ookinete. The PbWARP gene contained a single open reading frame encoding a putative secretory protein of 303 amino acids, with a von Willebrand factor type A module-like domain as a main component. Western blot analysis demonstrated that PbWARP was firstly produced 12 h after fertilization by maturing ookinetes as SDS-resistant complexes. Recombinant PbWARP produced with a baculovirus system also formed SDS-resistant high-order oligomers. Immuno-electron microscopic studies showed that PbWARP was randomly distributed in the micronemes. PbWARP homologues also exist in human malarial parasites, Plasmodium falciparum and Plasmodium vivax. Highly conserved primary structures of PbWARP homologues among these phylogenetically distant Plasmodium species suggest their functional significance and the presence of a common invasion mechanism widely utilized throughout Plasmodium parasites.

Amino Acid Sequence↗
PubMed2004

Meager genetic variability of the human malaria agent Plasmodium vivax.

Malaria is a major human parasitic disease caused by four species of Plasmodium protozoa. Plasmodium vivax, the most widespread, affects millions of people across Africa, Asia, the Middle East, and Central and South America. We have studied the genetic variability of 13 microsatellite loci in 108 samples from 8 localities in Asia, Africa, South America, and New Guinea. Only one locus is polymorphic; nine are completely monomorphic, and the remaining three are monomorphic in all but one or two populations, which have a rare second allele. In contrast, Plasmodium falciparum displays extensive microsatellite polymorphism within and among populations. We further have analyzed, in 96 samples from the same 8 localities, 8 tandem repeats (TRs) located on a 100-kb contiguous chromosome segment described as highly polymorphic. Each locus exhibits 2-10 alleles in the whole sample but little intrapopulation polymorphism (1-5 alleles with a prevailing allele in most cases). Eight microsatellite loci monomorphic in P. vivax are polymorphic in three of five Plasmodium species related to P. vivax (two to seven individuals sampled). Plasmodium simium, a parasite of New World monkeys, is genetically indistinguishable from P. vivax. At 13 microsatellite loci and at 7 of the 8 TRs, both species share the same (or most common) allele. Scarce microsatellite polymorphism may reflect selective sweeps or population bottlenecks in recent evolutionary history of P. vivax; the differential variability of the TRs may reflect selective processes acting on particular regions of the genome. We infer that the world expansion of P. vivax as a human parasite occurred recently, perhaps <10,000 years ago.

Animals↗
PubMed2001

Interspecies conservation of gene order and intron-exon structure in a genomic locus of high gene density and complexity in Plasmodium.

A 13.6 kb contig of chromosome 5 of Plasmodium berghei, a rodent malaria parasite, has been sequenced and analysed for its coding potential. Assembly and comparison of this genomic locus with the orthologous locus on chromosome 10 of the human malaria Plasmodium falciparum revealed an unexpectedly high level of conservation of the gene organisation and complexity, only partially predicted by current gene-finder algorithms. Adjacent putative genes, transcribed from complementary strands, overlap in their untranslated regions, introns and exons, resulting in a tight clustering of both regulatory and coding sequences, which is unprecedented for genome organisation of PLASMODIUM: In total, six putative genes were identified, three of which are transcribed in gametocytes, the precursor cells of gametes. At least in the case of two multiple exon genes, alternative splicing and alternative transcription initiation sites contribute to a flexible use of the dense information content of this locus. The data of the small sample presented here indicate the value of a comparative approach for Plasmodium to elucidate structure, organisation and gene content of complex genomic loci and emphasise the need to integrate biological data of all Plasmodium species into the P.falciparum genome database and associated projects such as PlasmodB to further improve their annotation.

Alternative Splicing↗
PubMed2006

The Plasmodium selenoproteome.

The use of selenocysteine (Sec) as the 21st amino acid in the genetic code has been described in all three major domains of life. However, within eukaryotes, selenoproteins are only known in animals and algae. In this study, we characterized selenoproteomes and Sec insertion systems in protozoan Apicomplexa parasites. We found that among these organisms, Plasmodium and Toxoplasma utilized Sec, whereas Cryptosporidium did not. However, Plasmodium had no homologs of known selenoproteins. By searching computationally for evolutionarily conserved selenocysteine insertion sequence (SECIS) elements, which are RNA structures involved in Sec insertion, we identified four unique Plasmodium falciparum selenoprotein genes. These selenoproteins were incorrectly annotated in PlasmoDB, were conserved in other Plasmodia and had no detectable homologs in other species. We provide evidence that two Plasmodium SECIS elements supported Sec insertion into parasite and endogenous selenoproteins when they were expressed in mammalian cells, demonstrating that the Plasmodium SECIS elements are functional and indicating conservation of Sec insertion between Apicomplexa and animals. Dependence of the plasmodial parasites on selenium suggests possible strategies for antimalarial drug development.

Amino Acid Sequence↗
PubMed2005

Increased polyclonal immunoglobulin reactivity toward human and bacterial proteins is associated with clinical protection in human Plasmodium infection.

BACKGROUND: Polyclonal B-cell activation is well known to occur in Plasmodium infections, but its role in pathogenesis or protection remains unclear. However, protective properties of natural antibodies have previously been demonstrated in other contexts. METHODS: Sera from asymptomatic and symptomatic Plasmodium-infected subjects locally detected in a survey study in the Brazilian Amazon, and from unexposed and exposed but presently uninfected control subjects, were assayed by a standardized quantitative immunoblot method allowing simultaneous detection of IgG or IgM reactivity to a large number of parasite-unrelated proteins. RESULTS: In subjects free of coinfection with hepatitis B virus, IgG reactivity to human brain antigens and Escherichia coli proteins was strikingly enhanced in asymptomatic Plasmodium-infected individuals when compared to such with clinical malaria symptoms, or to uninfected control subjects. This difference was most characteristic for limited exposure times (less than ten years locally, or 20 years in endemic areas). It was more significant than a similar trend found for IgG to Plasmodium falciparum antigens, and unrelated to parasitaemia levels. Asymptomatic subjects with comparatively short exposure characteristically showed relatively elevated IgG versus IgM reactivity. Polyclonal IgG reactivity appears triggered by previous P. falciparum but not Plasmodium vivax malaria. CONCLUSION: The observed difference in polyclonal antibody production seems related to intrinsic activation states of infected individuals, rather than to parasite-antigen specific immune responses. However, it appears influenced by preceding stimuli. This supports the idea that acquired clinical immunity may not exclusively depend on antigen-specific responses, but also on the individual polyclonal reaction.

Adolescent↗
PubMed2003

Why is the Plasmodium falciparum hexose transporter a promising new drug target?

Chemotherapy of malaria parasites is limited by established drug resistance and lack of novel treatment options. Intraerythrocytic stages of Plasmodium falciparum, the causative agent of severe malaria, are wholly dependent upon host glucose for energy. A facilitative hexose transporter (PfHT), encoded by a single-copy gene, mediates glucose uptake and is therefore an attractive potential target. The authors first established heterologous expression in Xenopus laevis to allow functional characterisation of PfHT. They then used this expression system to compare the interaction of substrates with PfHT and mammalian Gluts (hexose transporters) and identified important differences between host and parasite transporters. Certain Omethyl derivatives of glucose proved to be particularly useful discriminators between mammalian transporters and PfHT. The authors exploited this selectivity and synthesised an O-3 hexose derivative that potently inhibits PfHT expressed in oocytes. This O-3 derivative (compound 3361) also kills cultured P. falciparum with comparable potency. Compound 3361 acts with reasonable specificity against PfHT orthologues encoded by other parasites such as Plasmodium vivax, Plasmodium yoelii and Plasmodium knowlesi. Multiplication of Plasmodium berghei in a mouse model is also significantly impeded by this compound. These findings validate PfHT as a novel target.

Amino Acid Sequence↗
PubMed2005

Plasmodium species mixed infections in two areas of Manhiça district, Mozambique.

We compared the distribution patterns of individual Plasmodium species and mixed-species infections in two geographically close endemic areas, but showing environmental differences. Comparisons concerned circulating Plasmodium infections in both human and mosquito vector populations in the dry and wet seasons, at a micro-epidemiological level (households). Both areas revealed a very high overall prevalence of infection, all year-round and in all age groups. Plasmodium falciparum was the predominant species, being found in the vast majority of infected individuals regardless of the presence of other species. Plasmodium malariae and Plasmodium ovale occurred almost exclusively in mixed infections. Seasonal variation in P. malariae prevalence was observed in one area but not in the other. A decrease in P. malariae prevalence concurred with a marked increase of P. falciparum prevalence. However this was strongly dependent on age and when analysing infections at the individual level, a different pattern between co-infecting species was unveiled. Regarding transmission patterns, in both areas, P. falciparum gametocytes predominated in single infections regardless of age and P. malariae gametocyte carriage increased when its overall prevalence decreased.

Adolescent↗