Live-cell structural biology: towards the mechanics of exocytosis

Structure-function analyses are fundamental to understand the mode of action of the cellular machinery. However, cellular functions result from the concerted action of multiple protein assemblies and other cellular components, which complexity cannot be reconstituted in a tube. Thus, despite in vitro techniques can reconstruct isolated protein complexes up to the atomic scale, models where individual protein assemblies execute cellular functions are intrinsically limited.We have combined cell engineering, advanced live-cell imaging and computational integration of structural data to determine the 3D architecture of protein complexes directly in living cells. Using this approach, we have reconstructed the exocyst, a conserved multisubunit assembly that is responsible to tether secretory vesicles during exocytosis. The 3D architecture of the exocyst bound to a vesicle allowed us to start building a mechanistic model for exocytosis (Picco et al., Cell 2017).