Poster Presentation First Malaria World Congress 2018

Spatial organisation of protein export in Plasmodium falciparum (#442)

Thorey Jonsdottir 1 2 , Sarah Charnaud 1 , Paul Sanders 1 , Hayley Bullen 1 , Benjamin Dickerman 1 , Catherine Palmer 1 , Betty Kouskousis 1 , Halina Pietrzak 1 , Annamarie Laumaea 1 , Anna Erazo 1 , Emma McHugh 2 , Leann Tilley 2 , Brendan Crabb 1 2 3 , Paul Gilson 1 3
  1. Burnet Institute, Melbourne, VIC, Australia
  2. University of Melbourne, Melbourne
  3. Monash University, Melbourne

Plasmodium falciparum is responsible for the most severe form of malaria. Blood stage P. falciparum extensively remodels the erythrocytes it infects to help avoid host immunity and facilitate import of essential plasma nutrients to fuel rapid parasite growth. Around 500 effector proteins are synthesised by the parasite to carry out host cell renovation. These effector proteins need to be exported into the erythrocyte across an enveloping parasitophorous vacuole membrane (PVM). The Plasmodium translocon of exported proteins (PTEX) is thought to span the PVM and provide a selective channel that unfolds and then extrudes proteins across the PVM into the erythrocyte. Our aim was to see how PTEX binds to cargo proteins when a reporter cargo is made resistant to unfolding via addition of an inducer. We also wanted to determine if reporter cargo could recover and resume export after removing the inducer. Three different reporter cargoes were used to study protein export, all of which contained nanoluciferase, allowing us to quantitate protein export via bio-luminescence. Here we show that exported reporter proteins that inducibly resist unfolding can become trapped in regions co-localising with PTEX at the parasite surface/PVM, and have used super resolution methods to determine the sub-cellular location of this cargo. We show that when cargo is trapped via inducer, loop-like extensions grow from the PVM that appear to contain both trapped cargo and EXP2 but not additional PTEX components HSP101 and PTEX150. Following removal of the trap-inducing compound, export of the reporter proteins only partly recovers depending on their structure, possibly because much of the trapped cargo is spatially segregated in the loop regions away from the full PTEX complex. This suggests parasites have developed mechanisms to isolate unfoldable proteins from PTEX containing export zones to prevent disruption of protein export and reduced parasite growth.