PTEX helps efficiently traffic haemoglobinases to the food vacuole inPlasmodium falciparum

Abstract

A key element of Plasmodium biology and pathogenesis is the trafficking of ~10% of the parasite proteome into the host red blood cell (RBC) it infects. To cross the parasite-encasing parasitophorous vacuole membrane, exported proteins utilise a channel-containing protein complex termed the Plasmodium translocon of exported proteins (PTEX). PTEX is obligatory for parasite survival, both in vitro and in vivo, suggesting that at least some exported proteins have essential metabolic functions. However, to date only one essential PTEX-dependent process, the new permeability pathway, has been described. To identify other essential PTEX-dependant proteins/processes, we conditionally knocked down the expression of one of its core components, PTEX150, and examined which metabolic pathways were affected. Surprisingly, the food vacuole mediated process of haemoglobin (Hb) digestion was substantially perturbed by PTEX150 knockdown. Using a range of transgenic parasite lines and approaches, we show that two major Hb proteases; falcipain 2a and plasmepsin II, interact with PTEX core components, implicating the translocon's involvement in the trafficking of Hb proteases. We propose a model where these proteases are translocated into the PV via PTEX in order to reach the cytostome, located at the parasite periphery, prior to food vacuole entry. This work offers a another mechanistic explanation for why PTEX function is essential for growth of the parasite within its host RBC.

Aryl amino acetamides prevent the development ofPlasmodium falciparumrings via inhibition of the lipid transfer protein PfSTART1

“…PfGBP130, a known exported soluble protein (Jonsdottir et al, 2023;Perkins, 1988), was detected in the EqtII SN; PfSERA5, a soluble protein which localises in the PV of schizonts (Blackman, 2008;Jonsdottir et al, 2023), was enriched in the Sap SN; parasite cytosolic protein PfHSP70-1 was found mainly in the TX-100 SN. PfSTART1 was almost only detected in the TX100 fraction, indicating that it was either within the parasite, and/or associated with membranes.…”

“…Proteinase K protection assay. To further determine the localisation of PfSTART1 in schizonts, we conducted a proteinase K protection assay (Jonsdottir et al, 2023). Percollpurified schizonts were washed in PBS+PI, and lysed in 10x the pellet volume of EqtII (to achieve 100% hemolysis) for 10 min at 37°C.…”