Secretion of Plasmodium falciparum rhoptry protein into the plasma membrane of host erythrocytes.

Abstract

Abstract. The rhoptry is an organelle of the malarial merozoite which has been suggested to play a role in parasite invasion of its host cell, the erythrocyte. A monoclonal antibody selected for reactivity with this organelle identifies a parasite synthesized protein Of 110 kD. From biosynthetic labeling experiments it was demonstrated that the protein is synthesized midway through the erythrocytic cycle (the trophozoite stage) but immunofluorescence indicates the protein is not localized in the organelle until the final stage (segmenter stage) of intraerythrocytic development. Immunoelectron microscopy shows that the protein is localized in the matrix of the rhoptry organelle and on membranous whorls secreted from the merozoite, mAb recognition of the protein is dithiothreitol (DTT) labile, indicating that the conformation of the epitope is dependent on a disulfide linkage. During erythrocyte reinvasion by the extraceUular merozoite, immunofluorescence shows the rhoptry protein discharging from the merozoite and spreading around the surface of the erythrocyte. The protein is located in the plasma membrane of the newly invaded erythrocyte. These studies suggest that the ll0-kD rhoptry protein is inserted into the membrane of the host erythrocyte during merozoite invasion.RYTHROCYTE invasion by the malarial merozoite is a multi-step process, initiated by receptor-mediated binding of the parasite to its host cell (9). Electron microscopic studies show that penetration of the erythrocyte by merozoites involves invagination of the erythrocyte membrane where the apical end of the merozoite contacts the host cell (1). A moving membrane junction is formed and the contact maintained while the merozoite is internalized into a vacuole, which eventually forms the parasitophorous vacuole. Intracellular development of the parasite occurs inside this vacuole. Although it is well documented that invasion occurs by erythrocyte membrane invagination, the biochemical mechanisms whereby the parasite induces such a profound alteration in the rigid membrane-cytoskeletal organization of the erythrocyte are not understood.Endocytosis is not observed in erythrocytes except in druginduced instances (25). It has been proposed that the malarial parasite must initiate the membrane changes by some heretofore unknown process. Implicated in this unusual process are the rhoptries, a pair of electron dense organelles found in plasmodia and in other closely related members of the apicomplexa which are obligate intracellular parasites.Rhoptries of Toxoplasma, Sarcocystis and Besnoitia species have all been implicated in the invasion process. In Toxoplasma, a penetration enhancement factor possessing lytic activity has been identified, and is believed to be secreted by the rhoptries during invasion (15). In plasmodia the rhoptries are club-shaped organelles located randomly in the cytoplasm in the preinvasive stages of the parasite, that appear to subtend ducts to the exterior of the apical portion of the merozoite at the time of invasion. Electro...

Diversity and evolution of the rhoph1/clag multigene family of Plasmodium falciparum

“…Leaked RhopH complex, and therefore parasite-infected erythrocytes, are then potential targets of host immunity. Indeed, the PfRhopH complex and rhoptry-associated protein 2 (RAP-2, RSP-2), another malaria rhoptry protein, have been detected on the erythrocyte surface upon parasite attachment to erythrocytes [41,42]. The last possibility is that RhopH1/Clag, after release into the PV, may be distributed to the parasite-derived membranous network (i.e., Maurer's clefts) in the erythrocyte cytosol, where it is exposed to host immunity.…”

The use of confocal laser scanning microscopy to analyze the process of parasitic protozoon-host cell interaction

“…The observation that attached, but not internalized, parasites were labeled also suggests removal of surface components of the para- have shown that malaria merozoites labeled with fluorescent fatty acids transfer fluorescent material to the parasitophorous vacuole during invasion (41). Specific proteins (42,43) and lipids (41) are thought to be transferred from the apical organelles during invagination, contributing to the formation of the PVM. Taken together, the available data suggest that, after the initial contact of T. gondii tachyzoites with the surface of the host cell, interchange of surface components of the two interacting cells takes place.…”

Mononeme: A new secretory organelle in Plasmodium falciparum merozoites identified by localization of rhomboid-1 protease

“…Release from the erythrocyte triggers the movement of AMA1 to the cell surface where it functions in invasion (7,8). Similarly, rhoptries sequester a different set of proteins and their contents are released onto the erythrocyte surface (4,9), presumably to break the local cytoskeleton and to initiate formation of the parasitophorous vacuole. Taken together, these observations provide evidence for compartmentalization of parasite proteins into distinct organelles with related functions in invasion.…”