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J Biochem. 2018 Nov 22. doi: 10.1093/jb/mvy099. [Epub ahead of print]

The N-terminus of EXP2 forms the membrane-associated pore of the protein exporting translocon PTEX in Plasmodium falciparum.

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From the Burnet Institute, 85 Commercial Road, Melbourne, Victoria, Australia.
University of Melbourne, Melbourne, Victoria, Australia.
School of Science, RMIT University, Bundoora, Victoria, Australia.
Monash University, Melbourne, Victoria, Australia.


In order to facilitate a number of processes including nutrient acquisition and immune evasion, malaria parasites extensively remodel their host erythrocyte. This remodeling is to a large extent accomplished through protein export, a crucial process mediated by the PTEX translocon which is comprised of three core components, HSP101, PTEX150 and EXP2. EXP2 has been structurally and electrophysiologically shown to form the pore that spans the vacuole membrane enveloping the parasite. Here, we biochemically investigate the structure and function of EXP2. By differential alkylation we provide direct evidence that cysteines C113 and C140 form an intramolecular disulfide bond, while C201 is predominantly in a reduced state. We demonstrate that EXP2 possesses a protease resistant, membrane-associated, N-terminal region of approximately 20‚ÄČkDa that does not project into the infected erythrocyte cytosol, however its C-terminus does project into the vacuole space. We show that a putative transmembrane peptide derived from the N-terminal region of EXP2 is haemolytic and in a polymer-based osmotic protection assay, we demonstrate that this peptide forms a discrete haemolytic pore. This work provides further biochemical insight into the role, function and cellular arrangement of EXP2 as the pore-forming component for protein translocation.


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