Abstract

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).