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

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Abstract
Toxoplasma gondii is a protozoan parasite that has evolved a developmental morphotype called tachyzoite that navigates between cells and moves in and out of them in a wide repertoire of homeothermic hosts. Relying on a uniquely constant apicobasal bipolarity coupled to an actomyosin-driven retrograde surface flow, the tachyzoite has elaborated a molecular machinery to assemble transient anchoring contacts with the environment, which support the traction force required to power a typical helical gliding motility. Combining micropatterning with live, reflection interference contrast and expansion microscopies, we bring first nanoscale evidence that the tachyzoite needs to build only one apical anchoring contact with the substrate, thus spatially defining a minimal force transmission platform over which it can slide. We uncover that the apicobasal driven surface flow is set up in response to extracellular biochemical cues independent of adhesin release and tachyzoite-surface interactions, hence prior to motile activity. Furthermore, to identify the minimal adhesion requirements for helical gliding at the level of individual molecular species, we combine biochemical and biophysical quantitative assays based on tunable surface chemistry and quartz crystal microbalance with dissipation monitoring. These approaches uncover that glycosaminoglycan (GAG)-parasite interactions are sufficient to promote a productive contact for helical gliding and pave the way for the characterization of the structure and density of the molecules functionally engaged at this essential parasite-substrate mechanosensitive interface.

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