PROCESSING OF TOXOPLASMA ROP1 PROTEIN IN NASCENT RHOPTRIES

Secretion in the obligate intracellular parasite, Toxoplasma gondii, o ccurs through a number of regulated compartments. Among these are the epical organelles known as rhoptries which release their contents as p art of the invasion process. We are interested in the processing, targ eting and ultimate function of rhoptry proteins land have focused our analyses on rhoptry protein I (ROP1). In this paper, we address the is sue of processing: using a number of engineered forms of the ROP1 gene (introduced into a ROP1(-) background), we show that ROP1 is synthesi zed as a pre-pro-protein that is subject to proteolytic cleavages to r emove the pre-sequence and the 'pro' region, at the N-terminus. Using brefeldin A (BFA) and reduced temperature we show that this processing occurs late in the secretory pathway of the parasite, Immunolocalizat ion studies with epitope-tagged constructs indicate that processing is apparently occurring in the nascent rhoptries of dividing parasites. The results are discussed in the context of the targeting and possible function of the ROP1 protein. (C) 1998 Published by Elsevier Science B.V. All rights reserved.