Molecular mechanisms that integrate and control the actomyosin system in Toxoplasma gondii

Apicomplexans gliding motility is a form of locomotion powered by an actomyosin system, called the glideosome localized between the plasma membrane and the inner membrane complex (IMC). Transmembrane adhesins (MICs) are discharged by the micronemes on parasite surface. To generate movement, the glideosome must be linked to the cytoplasmic tails of the MICs. We have identified an armadillo repeat protein fulfilling all the criteria for a glideosome-adhesin connector (GAC). T. gondii possesses few actin-regulatory proteins with only three formins (FRMs) able to polymerize actin. By combining filamentous actin (F-actin) chromobodies with gene disruption we have assigned specific F-actin populations to each formin and distinct functions. The Apical Cap 9 (AC9) and AC10 are alveolin network protein localized to the most apical IMC plate. AC9 depleted parasites are deprived of the apical polar ring (APR) and the conoid, highlighting a new role of the apical cap region in apical complex stability