# A novel micronemal protein MP38 is involved in the invasion of merozoites into erythrocytes

## TL;DR

Researchers discovered a new protein in malaria parasites that helps them invade red blood cells, offering a potential target for vaccines.

## Contribution

The study identifies and functionally characterizes a novel Plasmodium vivax micronemal protein, PvMP38, and its role in erythrocyte invasion.

## Key findings

- PvMP38 localizes to micronemal organelles in both P. vivax and P. knowlesi merozoites.
- PvMP38 forms a high-affinity complex with Pv12 and Pv41, suggesting a functional interaction.
- CRISPR/Cas9 knockout of P. knowlesi mp38 impaired parasite growth, confirming its essential role.

## Abstract

The absence of an in vitro cultivation system for Plasmodium vivax hinders the exploration of molecular targets for vaccine development. To address this, functional studies often rely on alternative models, such as P. knowlesi, due to its genetic similarity to P. vivax. This study investigated the role of a novel micronemal protein, PvMP38 (PVX_110945), in both P. vivax and P. knowlesi merozoite invasion of erythrocytes. The full-length ectodomain of PvMP38 was expressed, and polyclonal antibodies were generated to assess its function. PvMP38 was confirmed to localize on micronemal organelle in both P. vivax and P. knowlesi merozoites. In vitro protein-protein interaction assays revealed that PvMP38 binds to Pv12 with high-affinity interaction. A conserved novel complex of Pv12-Pv41-PvMP38 was identified by immunoprecipitation of P. vivax antibodies on P. knowlesi schizont lysates. Linear epitopes of PvMP38 with high and moderate antigenicity were identified in clinical isolates of both species. Invasion inhibition assays demonstrated that a triple antibody combination targeting the PvMP38, Pv12, and Pv41 significantly reduced P. knowlesi merozoite invasion of erythrocytes compared to a single antibody. In addition, CRISPR/Cas9-mediated knockout of P. knowlesi mp38 markedly impaired parasite growth, underscoring its essential role during the asexual stage. These findings identify PvMP38 and its associated complex as promising targets for malaria interventions and highlight the utility of P. knowlesi as a model for investigating P. vivax erythrocyte invasion mechanisms.

This manuscript reported an effort in malaria eradication by identifying and functionally characterizing a novel Plasmodium vivax micronemal protein, PvMP38, involved in erythrocyte invasion. A narrow repertoire of an efficacious vaccine targeting P. vivax candidates is being developed due to the lack of continuous in vitro culture. This study addresses a gap in P. vivax research using P. knowlesi as a model for both genome editing and antibody functionality validation. By enhancing the protein-protein interaction screening framework, this study demonstrated that PvMP38 forms a complex with Pv12 and Pv41, opening the approaches to multi-antigen vaccines. The successful application of CRISPR/Cas9 gene editing techniques to disrupt its homolog, the pkmp38 gene, further assesses the protein’s significance in the growth and invasion of the parasite. These findings provided valuable insights into the biology of P. vivax and proposed PvMP38 as a promising candidate for malaria intervention strategies.