Molecular Partitioning during Host Cell Penetration by Toxoplasma gondii

Abstract

During invasion by Toxoplasma gondii, host cell transmembrane proteins are excluded from the forming parasitophorous vacuole membrane (PVM) by the tight apposition of host and parasite cellular membranes. Previous studies suggested that the basis for the selective partitioning of membrane constituents may be a preference for membrane microdomains, and this hypothesis was herein tested. The partitioning of a diverse group of molecular reporters for raft and nonraft membrane subdomains was monitored during parasite invasion by time-lapse video or confocal microscopy. Unexpectedly, both raft and nonraft lipid probes, as well as both raft and nonraft cytosolic leaflet proteins, flowed unhindered past the host-parasite junction into the PVM. Moreover, neither a raft-associated type 1 transmembrane protein nor its raft-dissociated counterpart accessed the PVM, while a multispanning membrane raft protein readily did so. Considered together with previous data, these studies demonstrate that selective partitioning at the host-parasite interface is a highly complex process, in which raft association favors, but is neither necessary nor sufficient for, inclusion into the T. gondii PVM.

Rhoptries: an arsenal of secreted virulence factors

“…The selective exclusion of transmembrane proteins anchored in the cytoskeleton suggests that filtering takes place on the cytoplasmic face of the plasma membrane. Alternatively, many proteins appear to gain access to the vacuole by virtue of partitioning into lipid rafts [3,4]. This raises the intriguing possibility that the moving junction is a mechanism to order lipids within the bilayer and thus influence the protein composition of the vacuolar membrane.…”

“…During invasion, the tight apposition of the host and parasite membranes forms a visible constriction known as the moving junction, which selectively restricts access of host proteins to the forming vacuole [3]. Most host cell membrane proteins are prevented from entering the forming vacuole by exclusion of transmembrane proteins with cytoplasmic tails and by a process that depends on protein partitioning in the lipid environment of the membrane [4]. This remarkable feat of invasion and vacuole remodeling takes a mere 15-20 seconds to complete, almost an order of magnitude faster than phagocytosis [2].…”

Host cell manipulation by the human pathogen Toxoplasma gondii

“…MIC and rhoptry neck proteins (RON) assemble on the parasite surface to form the moving junction (MJ) [10], a tight apposition of the parasite and host plasma membranes visible during cell invasion. The moving junction ensures the formation of the parasitophorous vacuole membrane (PVM) from the host cell membrane while largely excluding host membrane proteins from the forming PVM [11]. This partitioning strategy procures a non-fusigenic state of the PVM with host structures, avoiding the potential acidification and destruction of the PV contents by fusion with host cell lysosomes [12].…”

Host Cell Invasion by Toxoplasma gondii Is Temporally Regulated by the Host Microtubule Cytoskeleton

“…This causes an invagination of the plasma membrane resulting in the formation of the parasitophorous vacuole (PV), which is the compartment that the parasite resides in throughout its time in the host cell. However, host plasma membrane-associated proteins are selectively incorporated into the developing PV such that glycosylphosphatidylinositol (GPI)-linked proteins are included, while single-pass transmembrane proteins are excluded (7,24).…”