Geometric coupling of helicoidal ramps and curvature-inducing proteins in organelle membranes

Abstract

Cellular membranes display an incredibly diverse range of shapes, both in the plasma membrane and at membrane bound organelles. These morphologies are intricately related to cellular functions, enabling and regulating fundamental membrane processes. However, the biophysical mechanisms at the origin of these complex geometries are not fully understood from the standpoint of membrane-protein coupling. In this work, we focused on a minimal model of helicoidal ramps representative of specialized endoplasmic reticulum compartments. Given a helicoidal membrane geometry, we asked what is the distribution of spontaneous curvature required to maintain this shape at mechanical equilibrium? Based on the Helfrich energy of elastic membranes with spontaneous curvature, we derived the shape equation for minimal surfaces, and applied it to helicoids. We showed the existence of switches in the sign of the spontaneous curvature associated with geometric variations of the membrane structures. Furthermore, for a prescribed gradient of spontaneous curvature along the exterior boundaries, we identified configurations of the helicoidal ramps that are confined between two infinitely large energy barriers. Overall our results suggest possible mechanisms for geometric control of helicoidal ramps in membrane organelles based on curvatureinducing proteins.

Transport Phenomena in Fluid Films with Curvature Elasticity

“…At first glance, this result seems counter-intuitive since there is a non-zero density of curvature-inducing proteins on the membrane. But as we showed previously, for a uniform distribution of proteins with no-flux boundary conditions on the membranes, minimal surfaces are admissible solutions for the membrane geometry [49,50]. In this particular case, a flat membrane is the admissible solution for the boundary conditions associated with z.…”