The C-terminus of Toxoplasma RON2 provides the crucial link between AMA1 and the host-associated invasion complex

Host cell invasion by apicomplexan parasites requires formation of the moving junction (mj),a ring-like apposition between the parasite and host plasma membranes that the parasite migrates through during entry. the toxoplasma mj is a secreted complex including tgama1,a transmembrane protein on the parasite surface,and a complex of rhoptry neck proteins (tgron2/4/5/8) described as host cell-associated. how these proteins connect the parasite and host cell has not previously been described. here we show that tgron2 localizes to the mj and that two short segments flanking a hydrophobic stretch near its c-terminus (d3 and d4) independently associate with the ectodomain of tgama1. pre-incubation of parasites with d3 (fused to glutathione s-transferase) dramatically reduces invasion but does not prevent injection of rhoptry bulb proteins. hence,the entire c-terminal region of tgron2 forms the crucial bridge between tgama1 and the rest of the mj complex but this association is not required for rhoptry protein injection. © 2011 tyler,boothroyd.