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PubMed1996

Expression and immunogenicity of the C-terminus of a major blood-stage surface protein of Plasmodium vivax, Pv200(19), secreted from Saccharomyces cerevisiae.

The carboxy-terminus of the major merozoite surface protein of Plasmodium has been shown to be the target of protective immunity in a number of non-vivax malaria parasite species. In an effort to develop a protective vaccine for Plasmodium vivax, the most prevalent form of human malaria, we expressed in Saccharomyces cerevisiae the 19-kDa a carboxy-terminus of Pv200 as a His6-tagged, secreted polypeptide. Five of seven H-2 congenic mouse strains elicited antibodies that recognized yeast produced PV200(19) by ELISA. The vaccine appears to be immunogenic and widely recognized, and to contain one or more helper T cell epitopes that may allow boosting with subsequent natural infections.

Amino Acid Sequence↗
PubMed1981

Purine metabolism by the avian malarial parasite Plasmodium lophurae.

Extracts of normal duckling erythrocytes catabolized AMP to IMP, inosine and hypoxanthine; adenosine and adenine were not formed from AMP. When erythrocyte-free Plasmodium lophurae, prepared by antibody lysis, were incubated in the presence of [14C]hypoxanthine approximately 60% of the label was recovered as purine nucleotides and there was not evidence of extracellular alteration of added hypoxanthine. However, when adenosine was added to suspensions of antibody- or saponin-prepared parasites extensive conversion to inosine and hypoxanthine occurred. This conversion was found to be the result of parasite lysis with release of cytosolic purine salvage pathway enzymes; plasmodial surface membrane ecto-enzymes were not responsible for adenosine catabolism. It appears that in vivo the intracellular plasmodium utilizes the normal erythrocytic process of purine turnover to avail itself of hypoxanthine, the red cell's end product, and at the same time the parasite avoids direct competition for adenosine essential to erythrocyte survival. Since the blood plasma of infected ducklings contained increased amounts of hypoxanthine it is possible that P. lophurae also utilizes this as a purine source.

Adenine Nucleotides↗
PubMed1981

Isolation and characterisation of ribosomal RNA from the human malaria parasite Plasmodium falciparum.

Ribosomal RNA isolated from the malaria parasite Plasmodium falciparum consists of two species with molecular weight of 1.49 +/- 0.09 X 10(6) and 0.78 +/- 0.02 X 10(6) present in equimolar quantities. Their molecular weights are comparable with those of other protozoa but quite distinct from those of the human host. The overall base composition of the rRNA (40% G+C) is close to that of the rodent parasite Plasmodium berghei, unlike the latter, however, P. falciparum has no nick in the RNA from its large ribosomal subunit.

Animals↗
PubMed1981

Purine metabolizing enzymes of Plasmodium lophurae and its host cell, the duckling (Anas domesticus) erythrocyte.

Adenosine kinase, adenosine deaminase, hypoxanthine phosphoribosyltransferase, inosine-nucleoside phosphorylase, 5'-AMP deaminase and 5'-IMP nucleotidase were identified in cell-free extracts of duckling erythrocytes; no evidence for 5'-AMP nucleotidase and xanthine oxidase activity was found. The Km values for the duckling red cell enzymes were similar to those reported for human erythrocytes. Plasmodium lophurae extracts demonstrated similar enzyme activities except for 5'-AMP deaminase and 5'-IMP nucleotidase which were absent. It is proposed that during infection erythrocytic AMP is catabolized to IMP, inosine and hypoxanthine; the hypoxanthine is taken up by the plasmodium, utilized to form IMP, and this in turn is converted into adenine and guanine nucleotides.

AMP Deaminase↗
PubMed1984

The biosynthesis of the knob protein and a 65 000 dalton histidine-rich polypeptide of Plasmodium falciparum.

Previous studies have shown the association of an 80 kDa polypeptide (KP) with the knobs which develop on the membranes of erythrocytes infected with Plasmodium falciparum. KP was also found to share antigenic determinants with the histidine-rich protein of Plasmodium lophurae. In this study, ring stages of knobby (K+) and knobless (K-) variants of P. falciparum were used in pulse-chase experiments to elucidate the temporal sequence of the biosynthesis of KP. Analysis of radiolabeled parasite-polypeptides on SDS-polyacrylamide gels indicated that pulse-labeled KP has the electrophoretic mobility of a 75 kDa polypeptide and is subsequently chased to an apparently 80-85 kDa form. In addition to KP, antibodies raised against HRP immunoprecipitated a 65 kDa histidine-rich polypeptide from K- as well as K+ parasites. Differential incorporation of selected amino acids into KP and the 65 kDa polypeptide revealed some distinct differences between these two polypeptides as well as from HRP.

Animals↗
PubMed1985

Cytosolic protein kinase activity associated with the maturation of the malaria parasite Plasmodium berghei.

Seven cytosolic phosphoproteins with relative molecular masses of 110, 58, 52, 46, 38, 36 and 34kDa and isoelectric points between 4.2 and 5.0 are identified from the rodent malaria parasite Plasmodium berghei. Similar patterns of phosphorylated proteins are obtained from parasite cytosol after incubation of intact infected erythrocytes with [32P]orthophosphate, or from parasite cytosol incubated with [gamma-32P]ATP. The characteristics of the phosphorylation reaction are similar to the previously described Plasmodium protein kinase [Wiser, M.F., Eaton, J.W. and Sheppard, J.R. (1983) J. Cell. Biochem. 21, 305-314], suggesting that the same protein kinase is involved. More protein phosphorylation activity is associated with the mature parasites than the immature forms, suggesting that these phosphoproteins may play some role in the parasite's erythrocytic stage cycle.

Animals↗
PubMed1985

The primary structure of the rRNA insertions of Plasmodium lophurae.

The DNA sequences of the novel insertion in the 17s rRNA gene and the large insertion in the 25s rRNA gene in the cloned rDNA unit of the avian malaria parasite Plasmodium lophurae are presented, together with a partial sequence of the flanking regions, which code for the mature rRNA. The homology of the mature rRNA coding regions with the rRNA sequences of other eukaryotic organisms is extensive, indicating that the plasmodium rRNA is structurally similar to other eukaryotes. Sequence data also reveal that the region 3' to the insertion in the 17s rRNA contains a second small inserted DNA sequence, in contrast to other known small rRNA sequences. The region containing the 25s insertion shares sequence homology and some secondary structure characteristics with the terminal direct repeat of the Drosophila melanogaster transposable element copia. This is the first such sequence described in plasmodia. The direction of transcription of the cloned rDNA unit of P. lophurae has also been determined. As in other organisms, the direction of transcription is found to be 5' 17s-25s 3'.

Animals↗
PubMed1986

Mitomycin-C is an unreliable inhibitor for study of DNA synthesis in Plasmodium.

Cytophotometric studies on DNA synthesis during asexual and sexual development of Plasmodium berghei contradicted earlier conclusions on DNA synthesis in Plasmodium which were largely based on experiments in which mitomycin-C had been used as a DNA replication inhibitor. Therefore, the effect of mitomycin on intra erythrocytic asexual development and on microgametogenesis, fertilization and zygote/ookinete development of P. berghei was studied in vitro. All DNA-synthesizing stages (schizonts, exflagellating microgametocytes and zygotes) and also DNA synthesis itself in all such stages, are totally unaffected by mitomycin concentrations 10 times higher than that which inhibits normal development of the non-DNA-synthesizing rings and trophozoites. The results are explained by the mode of action of mitomycin.

Animals↗
PubMed1986

Membrane potential of erythrocytic stages of Plasmodium chabaudi free of the host cell membrane.

Free parasites were isolated from Plasmodium chabaudi-infected rat erythrocytes by N2-cavitation and purified on Percoll gradients. The membrane potential of the free parasites determined from the transmembrane distribution of the lipophilic cation, tetraphenylphosphonium, was -93 +/- 10 mV for late stage parasites and -90 +/- 3 mV for ring forms. Studies with intact infected erythrocytes demonstrated that the membrane potential of ring forms was much smaller compared to late trophozoites and schizonts and thus the present findings with free parasites suggest that host cell cytoplasmic factors may determine the magnitude of the parasite membrane potential. Both extracellular pH and [Na+] were found to modify the membrane potential of free parasites. Electrogenic protonophores, the H+-ATPase inhibitor dicyclohexylcarbodiimide and orthovanadate collapsed the potential of free parasites. Ouabain (or its membrane permeant derivative, strophanthidin), and oligomycin were without effect. These inhibitor studies suggest that an electrogenic H+-ATPase similar to that found in yeast generates in part the membrane potential of malaria parasites. Using weak acid distribution or a pH sensitive fluorescent dye, it was demonstrated that free parasites maintain an alkaline intracellular pH at extracellular pH greater than 6.5. The pH gradient was partially collapsed by orthovanadate or dicyclohexylcarbodiimide and by substitution of Na+ for K+ in the suspending buffer. The H+-ATPase and K+:H+ exchange may therefore both contribute to regulation of intracellular pH in Plasmodium.

Animals↗
PubMed1987

Detection of Plasmodium falciparum DNA using repetitive DNA clones as species specific probes.

Repetitive sequences were identified in genomic libraries of Plasmodium falciparum and analyzed for their potential use as specific DNA probes. Nucleotide sequencing revealed inserts composed of 21 base pair tandem repeats. Clone 26 containing an insert of 147 base pairs in M13mp18 was used in three different approaches as a probe to detect P. falciparum DNA: the replicative form of clone 26 was labeled by nick translation; the single strand DNA of clone 26 was labeled by primer extension and a two step sandwich assay was employed hybridizing single strand unlabeled clone 26 DNA to the target DNA (first step) and using nick translated M13 DNA in a second step to detect the vector part of clone 26. The most sensitive probes detected 25 pg of P. falciparum DNA after 2 h of film exposure, 3 pg after 14 h and 0.78 pg after 40 h. Hybridization to genomic blots of Plasmodium vivax and human DNA using clone 26 as a probe revealed that the 21 base pair repeats specifically hybridized with P. falciparum DNA while failing to react with either human or P. vivax DNA.

Animals↗
PubMed1988

Extremely diverged actin proteins in Plasmodium falciparum.

In a previous paper the nucleotide sequence of a complementary DNA coding for a Plasmodium falciparum actin protein (pf-actin I) has been described. Here we present evidence that the genome of this human malaria parasite encodes for still another actin protein (pf-actin II). Via nucleotide sequence analysis of its coding DNA we established the amino acid sequence of this protein. This sequence was compared with the pf-actin I sequence and those of a number of other actins. The comparative studies revealed that the amino acid sequence of pf-actin II is very diverged from the actins known thus far. The mutual amino acid sequence similarity between both Plasmodium actins is also very poor and in fact the observed value is the lowest ever seen between actins within one species. Furthermore, the studies suggest that the actin genes from sporozoa and ciliated protozoa, but not those from amoebae, have evolved from a common primitive ancestor. It is likely, however, that during evolution the actin sequences in these protozoa are not as well conserved as in other eukaryotic lineages.

Actins↗
PubMed1989

Structure and expression of the Plasmodium falciparum SERA gene.

Plasmodium falciparum, strain FCR3, genomic DNA that encodes the SERA gene of P. falciparum was isolated and sequenced. The SERA gene coding region was interrupted by 3 introns, the largest number observed, so far, in any Plasmodium gene. Two SERA gene alleles, allele I and allele II, were identified in the FCR3 strain, while only allele I was found in the Honduras-1 strain. Allele I mRNA was abundant in vivo during the late trophozoite and schizont stages. Allele II mRNA was either not expressed, or it was labile.

Alleles↗
PubMed1989

Identification of Plasmodium falciparum-infected mosquitoes using a probe containing repetitive DNA.

A cloned repetitive DNA sequence (rep20) was evaluated as a diagnostic probe specific for Plasmodium falciparum sporozoites using experimentally infected mosquitoes squashed directly on nylon filters. Head/thorax portions of mosquitoes, killed 14-16 days after ingesting P. falciparum-infected blood, gave positive signals when examined for the presence of P. falciparum sporozoite DNA by hybridisation. This correlated with the number of oocysts found in a sample of the same batch of mosquitoes examined by dissection. No positive signals were obtained with 50 Plasmodium berghei-infected mosquitoes probed with the rep20 sequence. The results indicate that a probe containing rep20 may be useful in the rapid and specific incrimination of vectors carrying P. falciparum sporozoites. The value of repetitive DNA in the diagnosis of malaria is discussed.

Animals↗
PubMed1989

Stage-specific expression and genomic organization of the actin genes of the malaria parasite Plasmodium falciparum.

Two different actin transcripts are found in the human malaria parasite Plasmodium falciparum. One of these is a 2.5-kb-long RNA found both in asexual blood stages and in the sexual stages (i.e., gametes/zygotes) of the parasite. This transcript is encoded by the P. falciparum (pf)-actin I gene. The second malarial actin gene, the pf-actin II gene, yields a 1.9-kb-long transcript which is formed solely in the sexual stages. Elucidation of the genomic organisation of these two Plasmodium actin genes showed that the pf-actin I gene does not possess any introns whereas the coding region of the pf-actin II gene is interrupted by a 368-bp intron. This intron has consensus splice junction sequences. Nucleotide sequence analysis of the 3' non-coding regions of the pf-actin genes revealed that these regions are quite long (pf-actin I, 250 bp; pf-actin II, 331 bp) and that these trailers do not share sequence similarity. Furthermore, the poly(A)+ addition sites of both actin mRNAs have now been identified. The 5' untranslated regions are also rather long; the sequenced areas lack sequence similarity and have, as do the 3' untranslated regions, a very high A + T content.

Actins↗
PubMed1989

Cloning and analysis of the gene encoding the 230-kilodalton merozoite surface antigen of Plasmodium yoelii.

The complete nucleotide sequence of the gene for the 230-kDa precursor to the major merozoite surface antigens (PMMSA) of Plasmodium yoelii YM has been determined. A single open reading frame of 5316 bp encodes a protein of calculated molecular mass 197,000. The deduced amino acid sequence contains potential signal peptide and membrane anchor sequences of 19 and 18 residues, respectively, and a region of six tandemly repeated tetrapeptides, Gly-Ala-Val-Pro. Comparison with the 195-kDa Plasmodium falciparum analogue (Pf195) at the amino acid level indicated an overall homology of approximately 30%, with areas of as high as 60% conservation. The tripeptide repeats present near the N-terminus of the Pf195 antigen are absent from the Py230 sequence. The PMMSA can be divided into 22 blocks based upon interspecies amino acid conservation.

Amino Acid Sequence↗
PubMed1991

Distinct lipid compositions of parasite and host cell plasma membranes from Plasmodium chabaudi-infected erythrocytes.

Mouse erythrocytes infected with early or late trophozoites of the malaria parasite Plasmodium chabaudi were fractionated into free parasites and host cell plasma membranes, and both fractions were analyzed for cholesterol content and the composition of phospholipids and total fatty acids. The major results are: (i) parasites contain only a very low level of cholesterol which is about one-tenth of that of host cell plasma membranes. (ii) Parasites also contain less sphingomyelin and phosphatidylserine as well as more phosphatidylcholine than host cell plasma membranes. (iii) Parasites contain less 18:0 and 18:1 and more 18:2 and 20:4 fatty acids than host cell plasma membranes. (iv) During intraerythrocytic growth of parasites from early to late trophozoites, the relative proportions of cholesterol and phospholipids remain largely unchanged in both parasites and host cell plasma membranes. However, significant changes occur in the fatty composition of both compartments. There is an increase in the 20:4 and a decrease in the 18:0 and 18:1 fatty acids. (v) Plasma membranes of infected and non-infected erythrocytes exhibit about the same cholesterol content and phospholipid composition, but differ in the total fatty acid composition. Our data suggest the existence of distinct mechanisms controlling the different lipid compositions of parasites and host cell plasma membranes in whole Plasmodium chabaudi-infected erythrocytes during intraerythrocytic development of parasites, though both compartments are known to depend on the supply of various lipids from the host.

Animals↗
PubMed1992

Intramolecular mapping of Plasmodium falciparum P126 proteolytic fragments by N-terminal amino acid sequencing.

Protein P126 (also called P140, P113, SERA, SERP1) is a major parasitophorous vacuole antigen of Plasmodium falciparum. This protein is processed upon merozoite release into 2 fragments of 73 kDa (P73) and 50 kDa (P50), which are found in the culture medium. P73 is composed of 2 polypeptides of 47 and 18 kDa linked by disulfide bridges. In the presence of leupeptin, an inhibitor of serine and cysteine proteases which inhibits merozoite release, a 56-kDa intermediate product (P56) is recovered in the culture medium instead of P50. In order to map these proteolytic fragments on the 126-kDa precursor, we purified them from Plasmodium falciparum culture medium by immunoadsorption, SDS-electrophoresis and Western blotting on PVDF membrane and determined the N termini of P126, P73 (P47 and P18), P50 and P56. Comparison of these sequences with the amino acid sequence deduced from the P126 gene allowed the mapping of the different fragments on the precursor. P47 was at the N-terminal and P18 at the C-terminal end of P126. P56 and P50 had the same N-termini and were located in the middle of P126. This latter result indicates that the proteolysis of P56-P50 occurs at the C-terminus of P56. The peptide bonds cleaved by leupeptin-insensitive activities are Glu-Thr and Gln-Asp; C-terminal sequencing of P50 will be needed to identify the leupeptin-sensitive cleavage site.

Amino Acid Sequence↗
PubMed1992

Random mating of natural Plasmodium populations demonstrated from individual oocysts.

DNA amplified from individual Plasmodium vivax oocysts, produced by feeding mosquitoes directly on naturally infected humans in Thailand, was used to study cross-mating of 2 polymorphs of the circumsporozoite (CS) gene, VK 210 and VK 247. Alleles were detected in matched blood parasites, sporozoites, and individual oocysts with oligoprobes specific to characteristic repeat units. Oocysts developing from 3 cases in which mixed alleles were present in the blood parasites had genotype frequencies, including hybrids, consistent with the Hardy-Weinberg equilibrium. There was apparently no barrier to hybridization of the 2 alleles nor a bias, as has been found in some laboratory experiments, favoring hybrid formation. These are the first measurements of cross-mating frequencies directly from natural Plasmodium infections and the first observations of genetic hybridization in P. vivax.

Alleles↗