The regulated secretory process appears to be essential for the succes of Toxoplasma. as an intracellular parasite. Moreover, this parasite represents a very interesting model for secretion studies since three different regulated secretory organelles are found within one cell. This suggests that the secreted proteins have to be sorted toward the right organelle. We are now studying the targetting of the GRA proteins in the dense granules. we have identified in GRA proteins a conserved and specific peptide sequence. We presently test by transfection experiments of Toxoplasma the involvment of this sequence in targetting a reporter protein in the dense granules.
To study in more details the sorting process in Toxoplasma, we propose identify molecules which interact with GRA proteins. This work will be performed in the two-hybrid system in yeast. Four of the eight GRA genes that have been cloned in our laboratory will be used in yeast in the two-hybrid system (i) to study the possible interactions between GRA proteins themselves and (ii) to identify regulating proteins involved in their intracellular trafficking.