Conoid extrusion regulates glideosome assembly to control motility and invasion in Apicomplexa.

Members of Apicomplexa are defined by apical cytoskeletal structures and secretory organelles, tailored for motility, invasion and egress. Gliding is powered by actomyosin-dependent rearward translocation of apically secreted transmembrane adhesins. In the human parasite Toxoplasma gondii, the conoid, composed of tubulin fibres and preconoidal rings (PCRs), is a dynamic organelle of undefined function. Here, using ultrastructure expansion microscopy, we established that PCRs serve as a hub for glideosome components including Formin1. We also identified components of the PCRs conserved in Apicomplexa, Pcr4 and Pcr5, that contain B-box zinc-finger domains, assemble in heterodimer and are essential for the formation of the structure. The fitness conferring Pcr6 tethers the PCRs to the cone of tubulin fibres. F-actin produced by Formin1 is used by Myosin H to generate the force for conoid extrusion which directs the flux of F-actin to the pellicular space, serving as gatekeeper to control parasite motility.