Structural determinants and function of chirality in the motion of malaria parasites

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Chirality is present in biological systems from the molecular through the cellular to the organismal level, but it is difficult to connect it across scales. Here we suggest to accomplish this for the members of the Plasmodium family, which are the causative agents of malaria. Two of its three motile forms, the sporozoites and the ookinetes, are known to move on helical trajectories in three-dimensional environments. The same holds true for the tachyzoite form of Toxoplasma gondii, a closely related member of the phylum apicomplexa and the causative agent of toxoplasmosis. There are several potential candidates for the molecular mechanisms underlying parasite chirality, including chiral elements in the microtubule corset, in the apical ring complex or in the actomyosin-mediated surface flow. Moreover, chirality in the cell movement might be determined by the interplay of such structural elements with the environment, including its geometrical and mechanical properties. The evolutionary benefits of helical motion might lie in efficient force transmission in elastic environments, but also in the efficiency of finding target structures or cells. We will combine advanced imaging, traction force microscopy and targeted mutations with mathematical models for self-propelled chiral particles and micromechanical models for Plasmodium sporozoites to identify the dominating molecular effect and to shed light on its evolutionary advantage for successful infections.