Absence of PEXEL-Dependent Protein Export in Plasmodium Liver Stages Cannot Be Restored by Gain of the HSP101 Protein Translocon ATPase.

Oriana Kreutzfeld,Josephine Grützke,Alyssa Ingmundson,Katja Müller,Kai Matuschewski

doi:10.3389/fgene.2021.742153

Abstract

Host cell remodeling is critical for successful Plasmodium replication inside erythrocytes and achieved by targeted export of parasite-encoded proteins. In contrast, during liver infection the malarial parasite appears to avoid protein export, perhaps to limit exposure of parasite antigens by infected liver cells. HSP101, the force-generating ATPase of the protein translocon of exported proteins (PTEX) is the only component that is switched off during early liver infection. Here, we generated transgenic Plasmodium berghei parasite lines that restore liver stage expression of HSP101. HSP101 expression in infected hepatocytes was achieved by swapping the endogenous promoter with the ptex150 promoter and by inserting an additional copy under the control of the elongation one alpha (ef1α) promoter. Both promoters drive constitutive and, hence, also pre-erythrocytic expression. Transgenic parasites were able to complete the life cycle, but failed to export PEXEL-proteins in early liver stages. Our results suggest that PTEX-dependent early liver stage export cannot be restored by addition of HSP101, indicative of alternative export complexes or other functions of the PTEX core complex during liver infection.

Highlights

Host cell remodeling is critical for successful Plasmodium replication inside erythrocytes and achieved by targeted export of parasite-encoded proteins
The first set of transgenic parasite lines expressed the Plasmodium export element (PEXEL)-containing reporter proteins under the control of the IBIS1 promoter, which is active in several life cycle stages, including in liver and blood stages
A similar confinement to the parasite and a stronger signal at the PV was detected for transgenic parasites that expressed CSP1-70-mCherry under the control of the strong and ubiquitous HSP70 promoter (Figure 1A), indicative that excessive protein may congest the PTEX translocon

Summary

Introduction

Host cell remodeling is critical for successful Plasmodium replication inside erythrocytes and achieved by targeted export of parasite-encoded proteins. A different class of exported proteins lack this motif, so-called PEXEL/HT negative exported proteins (PNEPs), but share the downstream translocation pathway (Grüring et al, 2012; Heiber et al, 2013). Both PEXEL and PNEP proteins are believed to be loaded into secretory vesicles to be transported and released into the PV. Once in the PV, proteins need to translocate the PVM to reach the erythrocyte cytoplasm, a process mediated by the Plasmodium translocon of exported proteins (PTEX) (de Koning-Ward et al, 2009)

Methods

Results

Conclusion