Uncovering the minimalist adhesive strategy of the Toxoplasma parasite for high-speed motility

Toxoplasma gondii is a intracellular protozoan and the etiological agent of toxoplasmosis, a set of chronic diseases. The T. gondii tachyzoite morphotype serves as model to study cell motility in simple living non swimming systems, since with a permanent apicobasal polarity, it bypasses the cell symmetry breaking needed for motility. Its moves by gliding front first between cells or into and out from host cells with a repetitive helical trajectory. Gliding is thought to proceed through a series of sub-membranous myosin motors which direct retrograde translocation of actin filaments along the parasite length, and power continuous sub-membranous forces. In this scenario, the tachyzoite secretes adhesins that, once exposed at the cell apex, engage with ECMs ligands, and flow backward with the newly formed actin filaments. We recently uncover a critical specific anchorage site for the generation and transmission of a periodic traction force during gliding (Pavlou et al, 2020). In this new study, we have interrogated the minimal spatial and molecular requirements for productive adhesion and force transmission beneath efficient gliding. To this end, we have combined submicron resolution micropatterning with live, quantitative reflection interference contrast microscopy and expansion microscopy. Using 4D image modeling, we bring first nanoscale evidence that the tachyzoite needs to build only one apical anchoring contact with the substrate, which spatially defines a minimal force transmission platform over which it slides. We clarify the relationship between surface flow and force generation, by monitoring microbead flow at 200 Hz and uncover that the apicobasal driven surface flow is set up independently from adhesin release and adhesion, prior to motile activity. Finally, to screen for the essential adhesion requirements for helical gliding at the single molecular species level in absence of any absorption of molecular components from the environment, we developed biochemical and biophysical quantitative assays using tunable surface chemistry and quartz crystal microbalance with dissipation monitoring. These approaches uncover the sufficiency of glycosaminoglycan (GAG)-parasite interaction to promote a productive contact for helical gliding and offer a new versatile platform to dissect the structure and density of the molecules functionally involved in the T. gondii gliding force.

Pavlou et al., ACS Nano 2020. doi: 10.1021/acsnano.0c01893