Dissecting EXP2 sequence requirements for protein export in malaria parasites

Area of Science:

• Parasitology
• Molecular Biology
• Cell Biology

Background:

• Apicomplexan parasites utilize a conserved pore-forming protein to transport molecules across the parasitophorous vacuole membrane (PVM).
• In malaria parasites (Plasmodium), EXP2 forms this nutrient pore and is also crucial for the protein export machinery, PTEX.
• GRA17 in Toxoplasma gondii is an ortholog of EXP2 involved in nutrient transport.

Purpose of the Study:

• To investigate the dual role of EXP2 in nutrient transport and protein export.
• To determine if the T. gondii ortholog, GRA17, can functionally complement EXP2's roles in Plasmodium parasites.
• To understand the structural and functional basis for EXP2's unique capabilities.

Main Methods:

• Expression of truncated EXP2, GRA17, and hybrid proteins in EXP2-knockdown Plasmodium parasites.
• Analysis of complementation of EXP2 function, including nutrient transport and protein export.
• Investigation of the role of specific protein domains and the impact of altered expression timing and levels.

Main Results:

• T. gondii GRA17 could not complement the protein export function of EXP2 in P. falciparum, even with modifications to key interaction regions.
• The central body region of EXP2 appears critical for PTEX assembly and function.
• Altered expression timing or levels of EXP2 impacted parasite viability but not protein export efficiency.

Conclusions:

• EXP2 is a unique pore-forming protein with specialized functions beyond nutrient transport in Plasmodium.
• The inability of GRA17 to complement EXP2's protein export role highlights specific structural requirements for PTEX function.
• EXP2's distinct transcriptional profile is essential for its dual role in nutrient exchange and protein export, contributing to parasite survival.