Sequence requirements for the export of the Plasmodium falciparum Maurer's clefts protein REX2

Area of Science:

• Malariology
• Molecular Parasitology
• Cell Biology

Background:

• Plasmodium proteins exported into host cells are crucial for parasite survival and virulence.
• The Plasmodium export element (PEXEL) or vacuolar targeting signal (VTS) is a known motif for protein export.
• PEXEL-negative exported proteins suggest an incomplete understanding of the malaria exportome.

Purpose of the Study:

• To investigate the export mechanisms of PEXEL-negative exported proteins in Plasmodium.
• To determine the role of specific protein domains in the export of REX2 and SBP1.
• To explore potential common export features between different PEXEL-negative proteins.

Main Methods:

• Site-directed mutagenesis to alter the N-terminal region of REX2.
• Analysis of protein export upon mutation of the REX2 transmembrane domain.
• Functional replacement experiments using domains from REX2 and SBP1.

Main Results:

• The N-terminal 10 amino acids of REX2 are essential for its host cell targeting and export.
• A single point mutation in the REX2 N-terminus abolishes protein export.
• The REX2 transmembrane domain is critical for export and, with the N-terminal region, can mediate export of other proteins.
• N-terminal and transmembrane domains of SBP1 can functionally substitute for those in REX2, indicating conserved export features.
• REX2 processing was observed, but unlike PEXEL proteins, no N-terminal acetylation was detected.

Conclusions:

• The N-terminal region and transmembrane domain of PEXEL-negative proteins like REX2 and SBP1 are key determinants of host cell export.
• These findings reveal novel export mechanisms beyond the PEXEL motif, contributing to a more complete understanding of the malaria exportome.
• The identified sequence features may represent a conserved export pathway for PEXEL-negative proteins in Plasmodium parasites.