Identification of merozoite secreted repertoire and immuno-pharmacological inhibition of a novel host-parasite interaction to block malarial infection

ABSTRACT Background During the intra-erythrocytic proliferation of Plasmodium falciparum , the host erythrocyte invasion is regarded as a complex and tightly regulated process comprising multiple receptor-ligand interactions, and numerous secretory molecules. Proteins secreted sequentially from apical organelles of merozoites serve as adhesins that play a crucial role in RBC invasion and can serve as vaccine and therapeutic targets. Methods Purified merozoites were triggered to discharge apical organelle contents by exposure to ionic conditions mimicking that of blood plasma. The secreted proteins were subjected to tandem mass spectrometry, and a well-characterized invasion ligand, RhopH3, was identified. A novel RhopH3 receptor, 14-3-3□ was unearthed using a Bacterial two-hybrid approach. This interaction was confirmed using multiple biophysical and biochemical approaches. We were successful in disrupting this interaction using a de novo peptide binder of 14-3-3□, and we subsequently assessed its effect on merozoite invasion. Results A total of 66 proteins were identified in the secretory fraction with apical organellar or merozoite membrane localization. The well-known adhesin, RhopH3 was also identified and its interaction with the host phosphopeptide-binding protein, 14-3-3□ was established. We also discovered a de novo peptide with the potency to disrupt this crucial interaction, thereby blocking merozoite invasion. Conclusion We, for the first time, report the secretory repertoire of plasmodium merozoite. Our study shows the importance of the erythrocyte protein, 14-3-3□ during the invasion process and paves the way for developing anti-malarial peptides or small molecules that inhibit the host-pathogen interaction, hence abrogating the invasion process.