Abstract
The protozoan parasite Toxoplasma gondii is equipped with a sophisticated secretory apparatus including three distinct exocytic organelles named micronemes, rhoptries and dense granules. We have dissected the requirements for targeting the microneme protein MIC3, a key component of T. gondii infection. We have shown that MIC3 is processed in a post-Golgi compartment, and that the MIC3 pro-peptide and epidermal growth factor (EGF) modules contain microneme targeting information. The minimal requirement for microneme delivery is defined by the pro-peptide plus any one of the three EGF domains. We have demonstrated that the cleavage of the pro-peptide, the dimerization of MIC3 and the chitin-binding-like sequence, which are crucial for host cell binding and virulence, are dispensable for proper targeting. Finally, we have shown that part of MIC3 is withheld in the secretory pathway in a cell cycle-dependant manner.