A proteomic view on the egress-related vesicles of malaria gametocytes [Exit-WS]

Abstract text

Introduction

Gametocyte egress from the host erythrocyte follows an inside-out mode during which the membrane of the parasitophorous vacuole ruptures prior to the erythrocyte membrane. Membrane rupture requires the exocytosis of specialized secretory vesicles of the parasites; i.e. the osmiophilic bodies (OBs) involved in rupture of the parasitophorous vacuole membrane, and vesicles, termed g-exonemes, that harbor the perforin-like protein PPLP2 needed for erythrocyte lysis. While several OB proteins are known, like G377 and MDV1/Peg3, the protein composition of the g-exonemes remains unclear.

Material/Method

We employed BioID analyses to unveil the interactomes of OBs and g-exonemes. BioID is a proximity labelling application for detecting putative protein-protein interactions. The method uses a promiscuous biotin ligase (BirA), fused to a bait protein that can be induced to biotinylate interacting and proximal proteins during a defined labelling period by biotin supplementation. TurboID represents an optimized version of the BioID, which uses a biotin ligase with higher activity and therefore decreases the labelling period dramatically. Biotinylated proteins can be isolated, analyzed via mass spectrometry (MS) and investigated as candidate interactors with the bait protein or as constituents within a subcellular domain.

Results

Here, we used high-resolution imaging and BioID methods to study the two types of egress vesicles in Plasmodium falciparum gametocytes. We show that OB exocytosis precedes discharge of the g-exonemes and that the two types of vesicles exhibit distinct proteomes. In addition to known egress-related proteins, our analyses revealed novel markers of OBs and g-exonemes, including components involved in protein processing and vesicle trafficking.

Discussion

Our data provide insight into the immense molecular machinery required for the inside-out egress of P. falciparum gametocytes.