Spatial organization of protein export in malaria parasite blood stages

• Published in: Traffic (Copenhagen, Denmark) Vol. 19; no. 8; pp. 605 - 623
• Main Authors: Charnaud, Sarah C., Jonsdottir, Thorey K., Sanders, Paul R., Bullen, Hayley E., Dickerman, Benjamin K., Kouskousis, Betty, Palmer, Catherine S., Pietrzak, Halina M., Laumaea, Annamarie E., Erazo, Anna‐Belen, McHugh, Emma, Tilley, Leann, Crabb, Brendan S., Gilson, Paul R.
• Format: Journal Article
• Language: English
• Published: Former Munksgaard John Wiley & Sons A/S 01.08.2018; Wiley Subscription Services, Inc
• Subjects: Dihydrofolate reductase; erythrocyte; Erythrocytes; luciferase; Malaria; Nutrients; Parasites; Parasitophorous vacuole; PEXEL; Plasmodium falciparum; protein export; protein trafficking; Protein transport; Proteins; PTEX; translocon; Plasmodium falciparum; PEXEL; PTEX; protein trafficking; protein export; translocon; luciferase; malaria; erythrocyte
• ISSN: 1398-9219; 1600-0854
• DOI: 10.1111/tra.12577

Malaria parasites export proteins into the human erythrocytes they infect. The exported proteins modify the erythrocyte thereby enabling parasite survival. A protein translocon called PTEX (complex of EXP2, PTEX150 and HSP101), encircles the parasite inside the erythrocyte and knockdown of PTEX appears to arrest protein export. To determine if PTEX directly unfolds and exports proteins we made reporters that were chemically resistant to unfolding. We found the reporters became bound to PTEX as if lodged in the complex implicating a direct role for PTEX in export. The compound WR99210 binds to exported reporter protein (Hyp1‐Nluc‐DH) preventing it from being unfolded and resulting in the reporter becoming trapped in the PTEX complex in the parasite. PV, parasitophorous vacuole; ER, endoplasmic reticulum; TVN, tubulo‐vesicular network and RBC, red blood cell. Plasmodium falciparum, which causes malaria, extensively remodels its human host cells, particularly erythrocytes. Remodelling is essential for parasite survival by helping to avoid host immunity and assisting in the uptake of plasma nutrients to fuel rapid growth. Host cell renovation is carried out by hundreds of parasite effector proteins that are exported into the erythrocyte across an enveloping parasitophorous vacuole membrane (PVM). The Plasmodium translocon for exported (PTEX) proteins is thought to span the PVM and provide a channel that unfolds and extrudes proteins across the PVM into the erythrocyte. We show that exported reporter proteins containing mouse dihydrofolate reductase domains that inducibly resist unfolding become trapped at the parasite surface partly colocalizing with PTEX. When cargo is trapped, loop‐like extensions appear at the PVM containing both trapped cargo and PTEX protein EXP2, but not additional components HSP101 and PTEX150. Following removal of the block‐inducing compound, export of reporter proteins only partly recovers possibly because much of the trapped cargo is spatially segregated in the loop regions away from PTEX. This suggests that parasites have the means to isolate unfoldable cargo proteins from PTEX‐containing export zones to avert disruption of protein export that would reduce parasite growth.