PT - JOURNAL ARTICLE AU - Gui, Long AU - O’Shaughnessy, William J. AU - Cai, Kai AU - Reetz, Evan AU - Reese, Michael L. AU - Nicastro, Daniela TI - Cryo-tomography reveals rigid-body motion and organization of apicomplexan invasion machinery AID - 10.1101/2022.04.23.489287 DP - 2023 Jan 01 TA - bioRxiv PG - 2022.04.23.489287 4099 - http://biorxiv.org/content/early/2023/01/14/2022.04.23.489287.short 4100 - http://biorxiv.org/content/early/2023/01/14/2022.04.23.489287.full AB - The apical complex is a specialized collection of cytoskeletal and secretory machinery in apicomplexan parasites, which include the pathogens that cause malaria and toxoplasmosis. Its structure and mechanism of motion are poorly understood. We used cryo-FIB-milling and cryo-electron tomography to visualize the 3D-structure of the apical complex in its protruded and retracted states. Averages of conoid-fibers revealed their polarity and unusual nine-protofilament arrangement with associated proteins connecting and likely stabilizing the fibers. Neither the structure of the conoidfibers nor the architecture of the spiral-shaped conoid complex change during protrusion or retraction. Thus, the conoid moves as a rigid body, and is not spring-like and compressible, as previously suggested. Instead, the apical-polar-rings (APR), previously considered rigid, dilate during conoid protrusion. We identified actin-like filaments connecting the conoid and APR during protrusion, suggesting a role during conoid movements. Furthermore, our data capture the parasites in the act of secretion during conoid protrusion.Competing Interest StatementThe authors have declared no competing interest.