Plasmodium SNARE proteins in exoneme discharge and merozoite egress

Malaria is caused by unicellular Plasmodium parasites, which repeatedly invade and lyse red blood cells (RBCs) in the human bloodstream. Intraerythrocytic infection is initiated by an extracellular Plasmodium merozoite which attaches to the host RBC and then pushes itself into a growing membrane sack which detaches from the host cell surface upon completion of invasion. Within this parasitophorous vacuole (PV), the parasite undergoes asexual schizogony transitioning through the ring, trophozoite and schizont stages of infection until a new generation of invasive daughter merozoites is formed. In a process called parasite egress, the merozoites then sequentially lyse the surrounding membranes of the PV and RBC to initiate another intraerythrocytic infection cycle. This specialized host cell exit pathway is essential for successful parasite replication in the human host and a validated drug target. During egress, Plasmodium merozoites discharge specialized secretory organelles that are loaded with regulatory proteases. Secretion of these so-called exonemes initiates a proteolytic cascade in the PV that ultimately results in host cell lysis. Thus, exoneme discharge is an essential nexus that couples intraparasitic signaling events to the extraparasitic machinery that mediates host cell dismantling. However, how exonemes fuse with the parasite plasma membrane (PPM) and what molecules control the process is currently unknown. In eukaryotic organisms, such fusion events are typically facilitated by SNARE (soluble N-ethylmaleimide-sensitive-factor attachment receptor) proteins. The genome of Plasmodium falciparum, the most virulent human malaria parasite, encodes 25 SNARE domain containing proteins and we found that two of them, called SNARE 1 and SNARE 20, fit the requirements for a possible involvement in exoneme discharge: (a) they are essential for parasite survival in the blood, (b) they localize to the PPM and (3) they are markedly upregulated late in schizogony. In acieiving the objectives, the aim is to achieve six distinct goals: (1) generate and validate conditional SNARE 1/20 knockout parasites, (2) determine the impact of SNARE 1/20 deletion on parasite development and egress, (3) assess whether SNARE 1/20 ablation blocks sequential membrane dismantling, (4) compare exoneme discharge in SNARE 1/20-null and control parasites, (5) determine whether SNARE 1/20 functions in membrane fusion, and (6) examine whether alternative exocytic processes in the parasite are affected by loss of SNARE 1/20. Together, these investigations hold the potential to significantly broaden our understanding of the molecular mechanisms underlying efficient host cell switching by the malaria parasite.

Project details

Basic Science

Jan 2024

Germany