Parasite Polypeptides Research Articles

Stage specific protein and nucleic acid synthesis during the asexual cycle of the rodent malaria Plasmodium chabaudi

The asexual intraerythrocytic stage of Plasmodium chabaudi develops synchronously in CBA mice. This in vivo synchrony has been exploited in in vitro pulse-labelling experiments to investigate the stage specificity of macromolecular synthesis by malaria parasites. Groups of mice were infected on day 0 with P. chabaudi and on day 3, individual mice were killed at three hour intervals, and the parasitised blood labelled in vitro for 2 h with radioactive precursors of protein or nucleic acid synthesis. By taking 11 samples covering one and one-third parasite division cycles, it was shown that the synthesis of many parasite polypeptides was restricted to defined morphological stages of parasite development. Other polypeptides were synthesised more or less continuously during the growth cycle. The synthesis of at least 6 polypeptides was confined to schizont or merozoite differentiation. RNA synthesis was shown to increase in rate steadily during parasite growth and to fall sharply during merozoite invasion. Approximately 40% of DNA synthesis was shown to occur during trophozoite growth, but the majority (60%) was confined to a short 4–6 h period at or just before schizogony.

Identification of a schizont- and species-specific surface glycoprotein on erythrocytes infected with rodent malarias

Erythrocytes infected with mature trophozoites of Plasmodium chabaudi and reticulocytes infected with P. berghei were labelled metabolically in vitro with [ 35S]methionine. The labelled cells were incubated with normal and immune serum and washed to remove unbound antibody. Solubilisation of the antibody-coated cells in detergent was followed by co-precipitation of antibody/antigen complexes and analysis of the immunoprecipitates by SDS-PAGE and fluorography. One major parasite polypeptide of 250 000 daltons was found to be exposed to antibody in both species. A labelled band of the same molecular weight could be identified by immunoprecipitation and SDS-PAGE analysis of P. chabaudi-infected cells that had been surface-labelled with periodate/NaB 3H 4. This molecule also incorporated [ 3H]glucosamine in short term cultures of mature parasitised erythrocytes. The results suggest that a 250 000 dalton glycoprotein which is synthesised only by late trophozoites or schizonts is exposed either on the surface of the infected erythrocyte, the surface of the merozoite, or both. Furthermore, the exposed portion of the molecule was not immunologically cross-reactive in the two Plasmodium species, but some cross reaction was detectable in total parasite lysates. The significance of these findings to protective immunity is discussed.

Molecular weight analysis of the major polypeptides and glycopeptides of [formula omitted

A soluble and an insoluble fraction of ultrasonicated Toxoplasma gondii (RH strain) tachyzoites were prepared by ultracentrifugation. The insoluble parasite fraction was solubilized by incubation in 1% sodium deoxycholate (DOC). The molecular weights (m.w.) of the polypeptides in the fractions were determined by sodium dodecyl sulphate (SDS) — polyacrylamide gel electrophoresis (PAGE). After comparison with the m.w. of the polypeptides of appropriate controls the soluble Toxoplasma fraction contained at least 9 parasite polypeptides with m.w. of 20K, 22K, 23K, 29K, 66K, 69K, 90K, 98K and 133K and the insoluble parasite fraction contained at least 8 Toxoplasma derived polypeptides with m.w. of 28K, 41K, 43K, 49K, 53K, 61K, 70K and 80K. The presence of glycosylated polypeptides was detected by incubation of sliced gels with | 125I| Concanavalin A (Con A). The soluble Toxoplasma fraction contained no major glycopeptide bands while the insoluble parasite fraction contained at least 3 glycosylated polypeptides of Toxoplasma origin with m.w. of 29K, 53K and 123K.