Plasmodium iophurae: immunization of Pekin ducklings with different antigen preparations

Physical characterization of histidine-rich protein from Plasmodium lophurae

The size and shape of Plasmodium lophurae histidine-rich protein have been determined by analytical centrifugation and electron microscopy. From the partial specific volume of 0.72 cc/g, the molecular weight was determined to be 43,000. The sedimentation velocity studies indicated a coefficient of 1.32 S in 0.9 M acetic acid (pH 3.5), monodispersity and significant asymmetry. Darkfield electron microscopy revealed the major species to be compact oblate spheroids 12 nm in width and extended filamentous particles of average length 35 nm by 1.5 nm. Analysis of the sequence of the protein by the method of Garnier et al. (J. Mol. Biol. (1978) 120, 97-120) predicted that 82% of its residues would be found in three long alpha-helices. The protein's CD spectrum has a strong resemblance to that of poly(L-histidine) at pH 4-5, where the homopolymer is thought to be in a right-handed alpha-helical form. A single helix containing 300 residues would be 45 nm long, the largest length found by electron microscopy. From the electron-microscopic data, sedimentation coefficients of 1.6 and 1.95 S, respectively, were calculated for flexible-coil and extended-rod models, in closer agreement with the measured value of 1.3 S than the value calculated for a spherical model. Thus, the major species in acetic acid is probably an incompletely extended rod which, as the pH is increased to neutrality, condenses to form spherical molecular aggregates seen in the malaria parasite.

Genomic organization, structure and possible function of histidine-rich proteins of malaria parasites

The current status of histidine-rich proteins in malaria parasites with regard to their genomic organization, protein structure and function is discussed, one of such protein present in an avian malaria parasite Plasmodium lophurae contains about 73% histidine and called as HRP (histidine-rich protein). Among human malaria parasites, in Plasmodium falciparum, only three such proteins have been described, namely knob protein also known as knob associated histidine-rich protein (KP or KAHRP), soluble histidine-alanine rich protein (soluble HARP or PfHRP II) and small histidine-alanine rich protein (SHARP) containing 8, 35 and 30% histidine contents respectively. With rapid emergence of powerful tools in molecular biology the genes of all these histidine-rich proteins have been cloned and sequenced within a short period of time. The genomic organizations of all these proteins are very much similar to each other, in each case the gene contains a signal peptide coding sequence (exon 1) followed by an intron. This intron is followed by the main coding region (exon 2) which has no further intervening sequences. In the main coding region of each gene, the histidine-rich sequences start after 25-30 amino acids from N-terminal end (75-90 nucleotides from 5' in exon 2). All the three histidine-rich proteins of P. falciparum share some homology with the HRP of P. lophurae; they all cross react with anti HRP and incorporate higher amount of exogenous histidine. The relationship between KP and HRP resides in the repeated polyhistidine sequences, (His) 6-9, from the core of the multiple tandem repeats of HRP, whereas, the peptide Ala-His-His is commonly shared by HRP and two other proteins of P. falciparum (soluble HARP and SHARP).(ABSTRACT TRUNCATED AT 250 WORDS)

Structure and organization of the histidine-rich protein gene of Plasmodium lophurae

Recombinant cDNA clones representing the carboxy-terminal portion of the histidine-rich protein of Plasmodium lophurae and the 3' untranslated region of the mRNA have been sequenced. Histidine accounts for 78% of the predicted amino acid sequence. The DNA and protein sequences in this region differ significantly from published sequences deduced from cloned genomic DNA of P. lophurae. Sequence data from two independent cDNA clones, comparison of restriction endonuclease sites present in genomic DNA, genomic and cDNA clones, gene titrations, S1 nuclease digestion of cDNA-mRNA hybrids and comparison of predicted and published data for the amino acid composition of the histidine-rich protein all suggest that P. lophurae contains one histidine-rich protein gene and that the sequence of the 3' coding region of this gene has been correctly deduced from the cDNA clones.

Sequence of a cDNA encoding a small polymorphic histidine- and alanine-rich protein from Plasmodium falciparum

We describe the expression in Escherichia coli, isolation by immunological screening and complete nucleotide sequence of a cDNA clone from the malaria parasite Plasmodium falciparum. The deduced amino acid sequence contains separate blocks of repetitive hexapeptide and pentapeptide sequences and we have confirmed that these represent epitopes by reaction of the corresponding synthetic peptides with human antibodies. As the predicted size is Mr 21,000 and the overall composition is 30% His and 29% Ala, the polypeptide has been termed the small histidine-alanine rich protein (SHARP). This polypeptide is highly polymorphic in different P. falciparum isolates and cross reacts immunologically with a distinct gene product of P. falciparum. Although it is related to the Histidine Rich Protein (HRP) of P. lophurae by virtue of its high His content, it shows no obvious sequence relationship to the HRP outside the repeats.

Primary structure and genomic organization of the histidine-rich protein of the malaria parasite Plasmodium lophurae

The nucleotide sequence of a complete genomic clone for the histidine-rich protein of Plasmodium lophurae has been determined. The deduced amino acid sequence of the mature protein shows numerous tandemly repeated units preceded by a signal and a pro peptide. The gene is interrupted by an intron with a separate exon coding for the signal peptide. The signal peptide-encoding exon detects multiple cross-hybridizing sequences in the parasite genome.

In vitro biosynthesis and core glycosylation of the histidine-rich protein of Plasmodium lophurae

We have characterized the early biosynthetic forms of the histidine-rich protein (HisRP), a major, granule-bound protein (Mr 58 000) of the avian malarial parasite Plasmodium lophurae. We have translated poly(A)-containing, size-selected parasite mRNA in the wheat germ cell-free system in the presence of [3H]histidine. HisRP was synthesized as a larger precursor (Mr 63 000). When dog pancreas microsomal membranes were present in the cell-free system during translation, a still larger form of HisRP (Mr 66 000) was detected. This larger form was segregated into the dog pancreas microsomal vesicles and was core glycosylated. Presumably, it corresponds to an intermediate form located in the parasite rough endoplasmic reticulum (RER). The difference in the Mr of approx. 8 000 between this RER associated 'pro' form and the granule-bound, mature form of HisRP suggests that proteolytic processing occurs upon transport from the RER to the granule. Segregation and core glycosylation were strictly coupled to translation and were not observed upon posttranslational addition of microsomal membranes. Thus, the early events in the biosynthesis of HisRP are similar to those established for secretory and lysosomal proteins.

Alkali-extraction of membranes from mouse erythrocytes infected with Plasmodium berghei

Alkali-extracted membrane material from hypotonically lysed Plasmodium berghei-infected mouse erythrocytes has been analyzed by dodecyl sulphate polyacrylamide gel electrophoresis and fractionated by discontinuous sucrose gradient centrifugation. Components characteristic for the protein pattern associated with P. berghei infection have been recovered in the alkali-extracted material. Parasite components, free of host cell membrane contamination, have been obtained as a high-density fraction from sucrose gradients. This fraction is characterized by polypeptides with apparent molecular weight of 71,000 and 52,000.