Biomembranes I

Mesoscale physics bridges the gap between the microscopic degrees of freedom of a system and its large-scale continuous behavior, highlighting those few quantities which are key to a multiscale process like, e.g., dynamin-driven fission of biomembranes. Dynamin wraps around the neck formed during endocytosis, for instance, and constricts it until severing occurs. Although ubiquitous and essential for life, the cooperation between the GTP-consuming conformational changes within the protein and the full-scale response of the lipid substrate has yet to be unraveled. In this talk, I will present an effective mesoscopic model from constriction to fission of lipid tubules, based on continuum membrane elasticity and implicitly accounting for ratchet-like power strokes of dynamins. The predicted fission site, overall geometry, and energy expenditure comply with the major experimental results, thus bolstering the idea that a continuous picture emerges soon enough to relate dynamin polymerization length and membrane rigidity and tension to the optimal pathway to fission. Surprisingly, dynamins found in in vivo processes seem to optimize their structure accordingly. Ultimately, I will shed light on real-time conductance measurements and predict the dependence of fission time on elastic parameters.