Translocation of ribosomal protein P0 onto the Toxoplasma gondii tachyzoite surface.

A ribosomal phosphoprotein P0 detected on the surface of the human malarial parasite Plasmodium falciparum (PfP0) has been shown to be recognised by invasion blocking antibodies. Using cross-reactive polyclonal antibodies against PfP0, the surface localisation has also been demonstrated on certain mammalian cells, yeast and Toxoplasma gondii. We sought to characterise the phenomenon of surface localisation in Toxoplasma using T. gondii P0 protein. Sequence analysis of a cDNA clone isolated from a T. gondii library showed marked similarity to PfP0, suggesting that T. gondii expresses an orthologous gene, TgP0. The expression of TgP0 was corroborated by Northern blot analysis revealing a transcript of 1.8 kb in size. Immunofluorescence analysis using anti-PfP0 indicated surface localisation of TgP0. To confirm surface translocation of the TgP0, tachyzoites were transfected with the HA-tagged TgP0 gene followed by immunofluorescence detection of the HA-tag. Surface translocation of transiently expressed TgP0 and blocking of tachyzoite invasion of human foreskin fibroblasts by anti-PfP0 antibodies suggest that P0 protein plays an important role in T. gondii invasion of human cells.