Enrichment and biochemical characterization of Toxoplasma gondii tachyzoite plasmalemma

The protozoan parasite Toxoplasma gondii possesses a triple surface membrane called the pellicle. This is made of an outer plasmalemma and an inner membrane complex lying under the plasmalemma. Using a high salt glycerol treatment followed by sonication, we have obtained a partial dissociation of the pellicle. A plasmalemma-enriched fraction was isolated on 0.7 M sucrose. It was identified by immunodetection of the tachyzoite major surface antigens. Protein content, resolved by SDS-PAGE, revealed that the surface protein SAG1 is the major component of the plasmalemma. The plasmalemma fraction is made of small vesicles (20-100 nm) which possess a low density (1.085-1.090 g/cm3 in sucrose) contrasting with other eukaryotic plasma membranes (1.12-1.16 g/cm3).