Export of a Toxoplasma gondii Rhoptry Neck Protein Complex at the Host Cell Membrane to Form the Moving Junction during Invasion

Abstract

One of the most conserved features of the invasion process in Apicomplexa parasites is the formation of a moving junction (MJ) between the apex of the parasite and the host cell membrane that moves along the parasite and serves as support to propel it inside the host cell. The MJ was, up to a recent period, completely unknown at the molecular level. Recently, proteins originated from two distinct post-Golgi specialised secretory organelles, the micronemes (for AMA1) and the neck of the rhoptries (for RON2/RON4/RON5 proteins), have been shown to form a complex. AMA1 and RON4 in particular, have been localised to the MJ during invasion. Using biochemical approaches, we have identified RON8 as an additional member of the complex. We also demonstrated that all RON proteins are present at the MJ during invasion. Using metabolic labelling and immunoprecipitation, we showed that RON2 and AMA1 were able to interact in the absence of the other members. We also discovered that all MJ proteins are subjected to proteolytic maturation during trafficking to their respective organelles and that they could associate as non-mature forms in vitro. Finally, whereas AMA1 has previously been shown to be inserted into the parasite membrane upon secretion, we demonstrated, using differential permeabilization and loading of RON-specific antibodies into the host cell, that the RON complex is targeted to the host cell membrane, where RON4/5/8 remain associated with the cytoplasmic face. Globally, these results point toward a model of MJ organization where the parasite would be secreting and inserting interacting components on either side of the MJ, both at the host and at its own plasma membranes.

Dissecting the interface between apicomplexan parasite and host cell: Insights from a divergent AMA–RON2 pair

“…Initially, parasites discharge RON2 into the host cell membrane where an extracellular portion (domain 3; D3) serves as a ligand for AMA1 displayed on the parasite surface (5)(6)(7)(8). Intriguingly, recent studies have shown that the AMA1-RON2 complex is an attractive target for therapeutic intervention (9)(10)(11)(12).…”

Un complexe moléculaire unique à l’origine de la motilité et de l’invasion des Apicomplexes

“…Cette protéine apparaît comme un anneau à l'intérieur du cercle formé par RON4 lors de l'invasion de mérozoïtes de P. falciparum [38]. Les trois protéines RON sont, elles, localisées au-delà de la membrane plasmique de la cellule hôte où elles pourraient interagir avec le cytosquelette cellulaire [39]. RON2 est insérée dans la membrane plasmique de la cellule hôte et interagit avec AMA1 à la surface du parasite [39] Repré-sentation schématique des premières étapes de l'invasion.…”

“…Les trois protéines RON sont, elles, localisées au-delà de la membrane plasmique de la cellule hôte où elles pourraient interagir avec le cytosquelette cellulaire [39]. RON2 est insérée dans la membrane plasmique de la cellule hôte et interagit avec AMA1 à la surface du parasite [39] Repré-sentation schématique des premières étapes de l'invasion. La sécrétion des protéines des micronèmes (MIC, AMA1) est induite par un signal dépendant du calcium intracellaire.…”

A Review: Competence, Compromise, and Concomitance—Reaction of the Host Cell To Toxoplasma gondii Infection and Development

“…The MJ forms when T. gondii attaches to receptors on the host cell and secretes MIC and rhoptry neck proteins (RONs), which assemble at the interface of the parasite and the host cell surface (Alexander et al, 2005;Cao et al, 2009). Recent studies have identified some key components of MJ that include microneme protein AMA1 and RON proteins RON 2, RON4, RON5, and RON8 (Besteiro et al, 2009). After establishing the moving junction, the parasite pushes itself forward, and the invagination of the plasma membrane around the invading parasite results in the formation of the PV (Fig.…”