Dual apical methyltransferases orchestrate motility initiation in apicomplexan parasites.

Abstract

Apicomplexan parasites such as Toxoplasma gondii initiate motility through rapid, spatially confined cytoskeletal activation at their apical end. While calcium-, lipid-, and kinase-based signalling pathways have been partially elucidated, how these cues are translated into mechanical force remains unclear. Here, we uncover a dual methyltransferase mechanism that orchestrates this process. We characterise TgPCKMT, a PreConoidal ring-associated lysine (K) MethylTransferase, as an essential upstream regulator of motility. TgPCKMT anchors the actin nucleator Formin-1 (TgFRM1) at the conoid, enabling conoid protrusion and F-actin assembly. Loss of TgPCKMT abolishes TgFRM1 recruitment, blocks conoid extrusion, and arrests invasion and egress despite preserved conoid structure. In contrast, the apical methyltransferase TgAKMT, previously linked to motility through recruitment of the glideosome-associated connector (TgGAC), acts downstream, disengaging from the conoid upon activation and likely promoting TgGAC-dependent force transmission. TgPCKMT depletion prevents TgAKMT translocation, revealing that actin assembly and lysine methylation are mechanistically coupled. Together, these findings define a two-step methylation regulatory module that coordinates actin nucleation with force propagation, uncovering methylation as a central regulatory axis for motility initiation in apicomplexan parasites.