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 proteins (PTEX) 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 colocalising 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 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.
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We thank the Australian Red Cross Blood Bank
for the provision of human blood, Jacobus
Pharmaceuticals for providing WR99210 and
Monash Micro Imaging and the Advanced
Microscopy Facility, University of Melbourne. We
also thank Freya Fowkes and Elisabeth WalshWilkinson
for analysis and technical assistance.
We would like to acknowledge the generous
assistance provided by Nicholas Williamson,
Ching-Seng Ang, Sean O’Callaghan and Shuai
Nie of the Mass Spectrometry and Proteomics
Facility at The University of Melbourne, Bio21
Institute. The authors gratefully acknowledge
funding from the Victorian Operational
Infrastructure Support Program received by the
Burnet Institute and for grants from the National
Health and Medical Research Council of Australia
(1068287, 1021560 and 637406).