PfAMA1 translocation and egress in 3D7-PfCDPK5DDKnL parasites. (A) SR-SIM IFA of [+] Shld-1 schizonts or [-] Shld-1 schizonts probed with anti-PfAMA1 antibodies. Representative parasites with micronemal and translocated PfAMA1 are shown. Bars, 2 mm. Synchronized 3D7-PfCDPK5DDKnL ring-stage parasites were maintained in the presence and absence of Shld-1 until 46 h.p.i., E64 was added, and cultures were incubated for an additional 6 h. Harvested schizonts were evaluated for the

localization of PfAMA1 (Fig. 3A). In schizonts grown in the presence of Shld-1 Shld-1 schizonts), 37% ± 8% had micronemal PfAMA1, and 63% ± 8% showed plasma membrane localization. In sharp contrast, 92% ± 2% of the schizonts grown in the

absence of Shld-1 ([-] Shld-1 schizonts) had micronemal PfAMA1, and only 8% ± 2% demonstrated plasma membrane localization. (C) SR-SIM IFAs performed on [+] Shld-1 and [-] Shld-1 3D7-PfCDPK5DDKnL schizonts demonstrating that the localization of PfEBA175 was not different in pre- and post-“egress trigger” [+] Shld-1 schizonts or in [-] Shld-1 schizonts. In both [+] and [-] Shld-1 schizonts, when PfAMA1 was apical, we found that

PfEBA175 was also apical. Interestingly, in the “post-egress trigger” [+] Shld-1 schizonts, we found that while PfAMA1 had been translocated, on the merozoite surface, PfEBA175 apparently remained apical. When released, PfEBA175-containing micronemes expose the ectodomain of PfEBA175 onto the surface of the apical end of the merozoite. The exposed PfEBA175 is processed by the rhomboid-like protease PfROM4

on the surface of the merozoite, shedding the ectodomain into the culture supernatant.

Absalon S, Blomqvist K, Rudlaff RM, DeLano TJ, Pollastri MP, Dvorin JD. Calcium-Dependent Protein Kinase 5 Is Required for Release of Egress-Specific Organelles in Plasmodium falciparum. MBio. 2018 9(1). pii: e00130-18