MyoL-Dependent Coupling of Preconoidal Rings to Conoid Is Required for Motility in Toxoplasma gondii

Abstract

Apicomplexan parasites are unified by their apical complex, a structure of cytoskeletal elements and secretory organelles. At its core lies the conoid, made of spiraling tubulin fibers essential for parasite motility and invasion. In Toxoplasma gondii, conoid extrusion and retraction through the apical polar ring is powered by Myosin H, ultimately regulating gliding motility. The conoid is capped by three preconoidal rings (PCRs), critical for extrusion and motility as they anchor formin 1, which produces filamentous actin needed for both processes. We demonstrate here that PCR composition and stability differ between daughter and mature cells and that Pcr2 and Pcr3 adopt a half-ring localization. The non-functional head containing Myosin-like protein MyoL, a previously unrecognized PCR component, is essential for gliding motility and invasion. Its depletion partially detaches PCRs from the conoid, highlighting its role as a mechanical tether. Targeted mutagenesis identifies the neck and tail regions of MyoL as critical for localization and function. Together, these findings illuminate the architecture and functional organization of the PCR in T. gondii, a structure conserved across several Apicomplexa.