Minimal Cell-Substrate Adhesion Conditions for Force Transmission during Toxoplasma Motility – MiniToxoAd

The interdisciplinary MiniToxoAd proposal interrogates how the protozoan parasitic microbe named Toxoplasma gondii interacts with and navigates through a variety of host extracellular matrices to establish intracellularly, which are the two obligatory conditions for guaranteeing T. gondii perpetuation. It is expected to have high scientific impact with substantial gain of knowledge on the crucial force transmission process mastered by the T. gondii motile tachyzoite to glide within extracellular matrices and move into target cells. The obtained results will offer a great opportunity to refine the current motility mechanistic model for T. gondii and related parasites clustered in the Apicomplexa phylum. The long-lasting model claims continuous force production along the body of the highly polarized zoite through the activity of a sub-membranous linear actomyosin motor, which (i) implies the engagement of surface exposed adhesins with extracellular ligands and (ii) works through the apico-basal translocation of these two connected systems and accounts for the typical gliding motility of T. gondii and other Apicomplexans. However, recent studies on T. gondii and on the related Plasmodium zoites, including ours, argue for higher complexity. They suggest the importance of specific adhesin-substrate interfaces, which promote building of the local and periodic gliding force, and our preliminary data strengthens this scheme. Indeed, we have demonstrated that the tachyzoite must build a privileged early contact between its apical pole and the substrate. The latter coincides with the site of a traction force that is transiently generated by the parasite to promote helical gliding. Using micropattern and live imaging, we have found that this adhesion platform is not just essential but sufficient for helical gliding. These findings strongly argue the relevance of resolving the molecular identity and functional properties of this polar adhesive contact, as it determines the parasite motile and invasive skills hence its fitness in vivo. Almost nothing is known on how the peculiar zoite adhesin-extracellular ligand interfaces are built and how they enable the development of a unique anchorage point involved in the transmission of the T. gondii force powering gliding. The MiniToxoAd program, through its conceptual framework that couples bioorganic chemistry, cell biology and biophysics, will take a step forward by providing quantitative data on the chemical and the physical requirements behind such parasite-substrate adhesion. To this end, we have built an interdisciplinary consortium made of a team specialized in cell biology and live imaging with long experience on the Toxoplasma mechanobiology and a partner team with state-of-the art skills in (supra)molecular design of biomimetic interfaces and their biophysical characterization. Benefiting on geographic proximity and on solid preliminary data collected through the consortium, the teams are ideally positioned to combine a set of high-resolution microscopy techniques with advanced surface functionalization protocols and complementary biochemical and biophysical approaches in order to fill the knowledge gap on the molecular events that direct one of the fastest but still enigmatic motility mode across eukaryotes. Besides, because of high and original technology content, the MiniToxoAd has also the potential to deliver new protocols for the design and characterization of functional interfaces to study biomolecular interactions (substrate-cell/cell-cell) beyond the T. gondii (or Apicomplexa) case(s) as well as new applications for advanced micropatterning of specific ligands of interest. Importantly, by enriching our technical advances in the use of nanotechnologies and providing well defined model systems allowing to tune the nature, the density, the 2D distribution and the fluidity of surface ligands, we expect to advance experimental research in the Parasitology community and beyond.