Identification of a non-exported Plasmepsin V substrate that functions in the parasitophorous vacuole of malaria parasites

Abstract

ABSTRACT Malaria parasites alter multiple properties of the host erythrocyte by exporting proteins into the host cell. Many exported proteins contain a five-amino acid motif called the Plasmodium export element (PEXEL) that is cleaved by the parasite protease Plasmepsin V (PM V). The presence of a PEXEL is considered a signature of protein export and has been used to identify a large number of exported proteins. The export of proteins becomes essential midway through the intraerythrocytic cycle—preventing protein export blocks parasite development 18–24 h after invasion. However, a genetic investigation revealed that the absence of the PEXEL protein PFA0210c (PF3D7_0104200) causes parasite development to arrest immediately after invasion. We now show that this protein is cleaved by PM V but not exported into the host erythrocyte and instead functions in the parasitophorous vacuole; hence, the protein was renamed PV6. We additionally show that the lysine residue that becomes the N-terminus of PV6 after processing by PM V prevents export. This is the first example of a native Plasmodium falciparum PM V substrate that remains in the parasitophorous vacuole. We also provide evidence suggesting that the parasite may produce at least one additional essential, non-exported PM V substrate. Therefore, the presence of a PEXEL and, hence, processing of a protein by PM V do not always target a protein for export, and PM V likely has a broader function in parasite growth beyond processing exported proteins. Furthermore, we utilized this finding to investigate possible requirements for protein export further. IMPORTANCE In the manuscript, the authors investigate the role of the protease Plasmepsin V in the parasite–host interaction. Whereas processing by Plasmepsin V was previously thought to target a protein for export into the host cell, the authors now show that there are proteins cleaved by this protease that are not exported but instead function at the host–parasite interface. This changes the view of this protease, which turns out to have a much broader role than anticipated. The result shows that the protease may have a function much more similar to that of related organisms. The authors also investigate the requirements for protein export by analyzing exported and non-exported proteins and find commonalities between the proteins of each set that further our understanding of the requirements for protein export.