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Plasmepsin X activates function of the PCRCR complex in P. falciparum by processing PfRh5 for binding to basigin and invasion of human erythrocytes

ABSTRACT: Plasmodium falciparum causes the most severe form of malaria in humans. The protozoan parasite develops within erythrocytes to mature schizonts, that contain more than 16 merozoites, which egress and invade fresh erythrocytes. The aspartic protease plasmepsin X (PMX), processes proteins and proteases essential for merozoite egress from the schizont and invasion of the host erythrocyte, including the leading vaccine candidate PfRh5. PfRh5 is anchored to the merozoite surface through a 5-membered complex (PCRCR), consisting of Plasmodium thrombospondin-related apical merozoite protein (PTRAMP), cysteine-rich small secreted protein (CSS), Rh5-interacting protein (PfRipr) and cysteine-rich protective antigen (CyRPA). We show that PCRCR is processed by PMX in micronemes to remove the N-terminal prodomain and this activates the function of the complex unmasking a form that can bind basigin on the erythrocyte membrane and mediate merozoite invasion. The ability to activate PCRCR at a specific time in merozoite invasion ensures invasion inhibitory epitopes are exposed to the immune system for a minimal time but also mask potential deleterious effects of its function until they are required. These results provide an important understanding of the essential roles of PMX and the fine regulation of PCRCR function in P. falciparum biology.

INSTRUMENT(S): timsTOF Pro

ORGANISM(S): Plasmodium Falciparum (isolate 3d7)

TISSUE(S): Blood

SUBMITTER: Laura Dagley

LAB HEAD: Professor Alan Cowman

PROVIDER: PXD039646 | Pride | 2023-04-05

REPOSITORIES: Pride

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Project description:Ubiquitylation is a common post translational modification of eukaryotic proteins. Protein ubiquitylation increases in the transition from intracellular schizont to extracellular merozoite in the asexual blood stage cycle of the human malaria parasite, Plasmodium falciparum (Pf). Here, we identify specific ubiquitylation sites of protein substrates in three intracellular parasite stages and extracellular merozoites; a total of 1464 sites in 546 proteins were identified. 469 ubiquitylated proteins were identified in merozoites compared with only 160 in the preceding intracellular schizont stage, indicating a large increase in protein ubiquitylation associated with merozoite maturation. Following merozoite invasion of erythrocytes, few ubiquitylated proteins were detected in the first intracellular ring stage but as parasites matured through trophozoite to schizont stages the extent of ubiquitylation increased. We identified commonly used ubiquitylation motifs and groups of ubiquitylated proteins in specific areas of cellular function, for example merozoite pellicle proteins involved in erythrocyte invasion, exported proteins, and histones. To investigate the importance of ubiquitylation we screened ubiquitin pathway inhibitors in a parasite growth assay and identified the ubiquitin activating enzyme (UBA1 or E1) inhibitor, MLN7243 (TAK-243) to be particularly effective. This small molecule was shown to be a potent inhibitor of recombinant PfUBA1, and a structural homology model of MLN7243 bound to the parasite enzyme highlights avenues for the development of P. falciparum specific inhibitors. We constructed a genetically modified parasite with a rapamycin-inducible functional deletion of uba1; addition of either MLN7243 or rapamycin to the recombinant parasite line resulted in the same phenotype, with parasite development blocked at the schizont stage. These results indicate that the intracellular target of MLN7243 is UBA1, and this activity is essential for the final differentiation of schizonts to merozoites. The ubiquitylation of many merozoite proteins and their disappearance in ring stages are consistent with the idea that ubiquitylation leads to their destruction via the proteasome once their function is complete following invasion, which would allow amino acid recycling in the period prior to the parasite’s elaboration of a new food vacuole.

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Plasmepsin X activates function of the PCRCR complex in P. falciparum by processing PfRh5 for binding to basigin and invasion of human erythrocytes

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