Efficient invasion by Toxoplasma depends on the subversion of host protein networks

Abstract

Apicomplexan parasites are important pathogens of humans and domestic animals, including Plasmodium species (the agents of malaria) and Toxoplasma gondii, which is responsible for toxoplasmosis. They replicate within the cells of their animal hosts, to which they gain access using a unique parasite-driven invasion process. At the core of the invasion machine is a structure at the interface between the invading parasite and host cell called the moving junction (MJ) . The MJ serves as both a molecular doorway to the host cell and an anchor point enabling the parasite to engage its motility machinery to drive the penetration of the host cell , ultimately yielding a protective vacuole . The MJ is established through self-assembly of parasite proteins at the parasite-host interface . However, it is unknown whether host proteins are subverted for MJ formation. Here, we show that Toxoplasma parasite rhoptry neck proteins (RON2, RON4 and RON5) cooperate to actively recruit the host CIN85, CD2AP and the ESCRT-I components ALIX and TSG101 to the MJ during invasion. We map the interactions in detail and demonstrate that the parasite mimics and subverts conserved binding interfaces with remarkable specificity. Parasite mutants unable to recruit these host proteins show inefficient host cell invasion in culture and attenuated virulence in mice. This study reveals molecular mechanisms by which parasites subvert widely conserved host machinery to force highly efficient host cell access.

Apicomplexan F‐actin is required for efficient nuclear entry during host cell invasion

“…Host cell invasion by apicomplexan parasites occurs through a tight junctional ring (TJ), established by the parasite upon secretion of its rhoptry content . Previous studies demonstrated that the TJ is anchored to the host cell cortex via its interaction with host cell factors thereby acting as an anchor for traction force exerted by the parasites acto‐myosin system . In addition, compressive forces, caused by the host cell at the TJ, require the deformation of the parasite during invasion, which appears to be counterbalanced to ensure integrity of the parasite .…”

Intersection of endocytic and exocytic systems in Toxoplasma gondii

“…The presence of a plant‐like lysosome and a plant‐specific proton pump (TgVP1) within the T. gondii endolysosomal system suggests that endocytic trafficking in T. gondii may resemble plants as proposed by Pieperhoff et al However, exocytic trafficking of proteins destined for the parasite’s regulated secretory organelles, the micronemes and rhoptries, proceeds through the TGN and ELCs, and requires clathrin, dynamin and Rab5 for transit . In contrast to the ingestion pathway, which leads to the destruction of its cargo, most microneme and rhoptry proteins have propeptides that are cleaved off during transit to the microneme and rhoptry organelles, but must otherwise remain intact to orchestrate parasite invasion, egress and defense against host immune attack . Without these exocytic proteins and organelles, the parasite cannot establish a successful infection.…”

“…[9][10][11][12][13][14][15][16] In contrast to the ingestion pathway, which leads to the destruction of its cargo, most microneme and rhoptry proteins have propeptides that are cleaved off during transit to the microneme and rhoptry organelles, but must otherwise remain intact to orchestrate parasite invasion, egress and defense against host immune attack. [17][18][19][20][21][22][23][24][25][26][27] Without these exocytic proteins and organelles, the parasite cannot establish a successful infection.…”

Apicomplexan F-actin is required for efficient nuclear entry during host cell invasion

“…On the extracellular side, the exposed domain of the RON2 member binds the micronemal transmembrane protein AMA1 exposed on the parasite surface, resulting in the formation of a stable, junctional complex (Besteiro et al, 2011). The TJ is further anchored to the host cell cortex by de novo formation of F-actin through the recruitment of actin-nucleating proteins (Bichet, Joly et al, 2014) , (Guerin, Corrales et al, 2017). During host cell invasion the parasites use their actomyosin motor to pass through the TJ.…”