The pro region of Toxoplasma ROP1 is a rhoptry-targeting signal.

The rhoptries of Toxoplasma gondii are regulated secretory organelles involved in the invasion of host cells. Rhoptry proteins are synthesised as pre-pro-proteins that are processed first to pro-proteins upon entrance into the secretory pathway, then processed again to their mature forms late in the secretory pathway. The pro-mature processing site of the rhoptry protein ROP1 has been determined, paving the way for understanding the role of the pro region in rhoptry protein function. We demonstrate here that the ROP1 pro region is sufficient for targeting a reporter protein (amino acids 34-471 of the Trypanosoma brucei VSG117 protein) to the rhoptries. These results, together with our previous work showing that rhoptry targeting is unaffected by deletion of the pro region, indicate that the ROP1 protein contains at least two signals that can function in rhoptry targeting.