Elucidating the molecular basis for conoid extrusion in Toxoplasma gondii

ABSTRACT Chronically infecting a third of the world’s population, Toxoplasma gondii (T. gondii) is the most successful human pathogen. The parasite owes part of its success to a specialized apical structure that is built to assist host cell invasion. This apical complex contains a tubulin-based organelle called the conoid which becomes extruded during cell motility by an unknown mechanism involving actin, myosin (MyoH) and a formin (formin 1). The goal of this proposal is to reconstitute these core elements of the apical complex in vitro to gain a mechanistic understanding of how the conoid is extruded. In our previous study (published in Nature Communications), we visualized the polymerization of individual T. gondii actin filaments in real time. This work will be the basis for studying the properties of formin 1 and MyoH. In Aim 1, we will study the biophysical features of MyoH and determine if force generation is necessary for conoid extrusion. In Aim 2, we will visualize the nucleation of T. gondii actin from formin 1 in vitro and then reconstitute the protein with MyoH and actin to directly visualize how these components cooperate to drive conoid extrusion. By taking a biophysical approach, results to these studies will provide long sought after mechanistic details of conoid extrusion and cell motility, which will greatly inform future development of next generation drugs that target these essential proteins.