A lipid-binding protein mediates rhoptry discharge and invasion in Plasmodium falciparum and Toxoplasma gondii parasites

Catherine Suarez,Raghavendran Ramaswamy,Martin J Boulanger,Gaëlle Lentini,Boris Striepen,Allan L Chen,Laurence Berry-Sterkers,Maryse Lebrun,Eleonora Aquilini,Peter Bradley,Michael Cipriano,Marjorie Maynadier

doi:10.1038/s41467-019-11979-z

Abstract

Members of the Apicomplexa phylum, including Plasmodium and Toxoplasma, have two types of secretory organelles (micronemes and rhoptries) whose sequential release is essential for invasion and the intracellular lifestyle of these eukaryotes. During invasion, rhoptries inject an array of invasion and virulence factors into the cytoplasm of the host cell, but the molecular mechanism mediating rhoptry exocytosis is unknown. Here we identify a set of parasite specific proteins, termed rhoptry apical surface proteins (RASP) that cap the extremity of the rhoptry. Depletion of RASP2 results in loss of rhoptry secretion and completely blocks parasite invasion and therefore parasite proliferation in both Toxoplasma and Plasmodium. Recombinant RASP2 binds charged lipids and likely contributes to assembling the machinery that docks/primes the rhoptry to the plasma membrane prior to fusion. This study provides important mechanistic insight into a parasite specific exocytic pathway, essential for the establishment of infection.

Highlights

Members of the Apicomplexa phylum, including Plasmodium and Toxoplasma, have two types of secretory organelles whose sequential release is essential for invasion and the intracellular lifestyle of these eukaryotes
We show that RASP2 contains C2 and Pleckstrin Homology-like domain (PH)-like domains that contribute to phosphatidic acid (PA) and PIP2 binding and cooperate for rhoptry secretion in a Ca2+-independent manner
The presence of lipid binding domains such as C2 and PH domains are a hallmark of proteins that act as regulators of calcium-dependent dense core vesicle exocytosis[24]

Summary

Introduction

Members of the Apicomplexa phylum, including Plasmodium and Toxoplasma, have two types of secretory organelles (micronemes and rhoptries) whose sequential release is essential for invasion and the intracellular lifestyle of these eukaryotes. The signalling pathways for rhoptry discharge, the molecular mechanisms governing rhoptry docking and fusion to the extreme apical end of the parasite (exocytosis), and the subsequent export of rhoptry contents across the host cell membrane, remain enigmatic This is in stark contrast to the abundant literature describing the secretion mechanism of the microneme organelles[2,3]. Rhoptry secretion can only be observed during the process of invasion, suggesting that this relies on direct recognition between the surface molecules of the parasite apex and receptor molecules on the host cell membrane In support of this hypothesis, the microneme protein EBA175, released at the surface of the merozoites of P. falciparum, binds Glycophorin A at the red blood cell surface. Our findings support a role for RASP2 in docking/priming the rhoptries to the parasite plasma membrane

Methods

Results

Conclusion