Detection and Immunolocalization of Human Erythrocyte Spectrin Immunoanalogues in Toxoplasma gondii (Protozoan, Parasite)

ABSTRACT. We demonstrated here the presence of proteins antigenically related to human erythroid spectrin in the parasitic protozoan Toxoplasma gondii . A high molecular weight doublet (M, 245-240,000), present in equimolar ratio, and low molecular weight polypeptides (M, 75,000) were reacted with monoclonal and polyclonal anti-human erythroid spectrin antibodies on electroblotted nitrocellulose sheets. Indirect immunofluorescence assay clearly showed that these proteins were localized in the anterior pole of the organism. Immunogold staining further revealed specific labeling of conoid, rhoptries, micronemes, and dense granules of the apical complex. The presence of the M, 245–240,000 doublet and the M, 75,000 spectrin-like proteins in the anterior pole of T. gondii may probably be consistent with a structural stabilizer function in its organciles which are suspected to be involved in the process of host cell invasion.     

Myosin-Like Protein (MR 175,000) In Gregarina Blaberae

ABSTRACT. A myosin-like protein (M_r 175,000) was detected in the parasitic protozoan Gregarina blaberae , by both immunofluorescence and immunoblotting of one- and two-dimensional electrophoresis gels using anti-myosin antibodies. This protein was present in the trophozoite ghost but not in the cytoplasmic extract, nor in extract from the sexual stage, suggesting a protein-stage-dependent expression. the protein tightly bound to the cortical membranes was insoluble at low ionic strength, or in detergent solutions, but could be extracted from Gregarina ghosts by 6 M urea in high ionic strength solution (0.5 M NaCI) and in the presence of reducing agents (20 mM DTT). the protein was localized by indirect immunofluorescence in the cortex of the epimerite, in the fibrillar disc (the socalled septum) separating the proto- and the deutomerite segments, in the contractile ring or sphincter at the top of the protomerite, and as longitudinal lines underlying the G. blaberae epicyte folds. the presence of both actin-like and myosin-like proteins would be consistent with a role in gliding and other cell motility processes of this parasite.