rhoptries

Rhoptries are specialized secretory organelles found at the apex of invasive zoites in many apicomplexan parasites, including Plasmodium species and Toxoplasma gondii. They consist of a bulb-shaped rhoptry body and a slender rhoptry neck, connected to the parasite’s cytoskeleton. The organelle contains a repertoire of rhoptry proteins (ROPs) and rhoptry neck proteins (RONs). ROPs include rhoptry kinases and other effector proteins, while RONs participate in forming the moving junction at the parasite–host interface.

During host cell invasion, the parasite first secretes microneme contents to mediate attachment, followed by rapid discharge of rhoptry contents. RON proteins are inserted into the host cell plasma membrane, and ROPs are delivered into the parasitophorous vacuole or its membrane. The coordination of rhoptry secretion with other secretory organelles helps remodel the host cell and establish a parasitophorous vacuole that protects the parasite from host defenses. Some rhoptry proteins modulate host signaling pathways and immune responses, contributing to virulence and successful intracellular survival.

Occurrence and variation: rhoptries are present in a broad range of apicomplexans, including Plasmodium, Toxoplasma, Neospora, and Eimeria, though their number, organization, and specific protein complements can vary by species and life stage.

Research and significance: rhoptries are central to understanding how invasive apicomplexans invade host cells and manipulate host biology. Components of the rhoptry secretion pathway are investigated as potential targets for vaccines or therapeutics aimed at inhibiting invasion or parasitophorous vacuole formation.