Project Summary: Approximately 20% of the people on Earth are permanently infected with the unicellular parasite, Toxoplasma gondii. T. gondii is one of the leading causes of congenital neurological defects in humans, and an agent for devastating opportunistic infections in immunocompromised individuals. Ocular toxoplasmosis is one of the most common retinal infections and can lead to blindness. As an obligate intracellular parasite, T. gondii must first invade cells of its host in order to replicate. In the preliminary study, we found that the disruption of an iconic structure in T. gondii, the conoid, is linked to drastically impaired invasion. This is an aspect of invasion that has not been explored, as previous work on invasion has mainly centered on the regulation and activity of the actomyosin motor complex and protein secretion from specialized membrane-bound organelles. To explore this new direction, we propose two complementary aims to (a) determine the function of the conoid in host cell invasion (Aim 1), and (b) elucidate how this novel cytoskeletal complex is constructed (Aim 2). Using the mutants we have generated, Aim 1 will determine whether the conoid facilitates invasion by secretion, motility, directly assisting the physical interaction between the parasite and the host cell during attachment, or overcoming the cortical tension of the host cell. Aim 2 will identify and characterize structural determinants of the conoid by integrating gene discovery with structural and functional analyses. We will combine state of the art imaging, biophysical, biochemical, and evolutionary approaches. This comprehensive strategy will greatly enhance our ability to identify novel components in this unique structure as drug targets.

Project Narrative: Toxoplasma gondii infections in immunocompromised individuals and unprotected fetuses can have devastating consequences, including the development of lethal Toxoplasma encephalitis. Ocular toxoplasmosis is one of the most common retinal infections and can lead to blindness. Our study on parasite invasion into the host cell will contribute to the rational selection of novel chemotherapeutic targets for preventing and controlling the damages caused by this parasite.