A micromechanical model for interactions of curvature sensing septin filaments with membrane

Cells reconfigure their shape in micron-scale in response to internal and external forces. Septins are filament-forming GTP-binding proteins that can sense curvature in micron-scale by preferentially accumulating in membrane regions with high curvature. Yet, the underlying mechanisms by which a nanoscopic septin hetero-octamer senses curvature in micron-scale remains unclear. We combine biophysical modeling and experiments and propose a micromechanical model for interactions of septin filaments with membranes. We propose that the rate of attachment of septins filaments to membranes is controlled by a combination of membrane’s thermal and stored elastic energy, while the rate of detachment is controlled by the bending energy of the curved membrane-bound septin filaments. Moreover, our model predicts a qualitative change in septins curvature sensing as they assemble into micron-scale filaments in larger concentrations. We verify these predictions experimentally, by measuring the attachment/detachment kinetics under different bulk concentrations of septins on beads of different radii, covered with lipid bilayer.