Laboratoire Matière et Systèmes Complexes

Shapes and dynamics of lipid membrane systems: from pulsatile artificial vesicles to intracellular membrane structures

Morgan Chabanon

Abstract: Cellular lipid bilayers are found to display incredibly diverse shapes and dynamics, both at the plasma membrane and at membrane bound organelles. To understand the relationship between the complex physical properties of lipid membranes and their biological functions, it is often necessary to combine insights from artificial and biological membrane systems. In this talk we will illustrate both of these approaches through examples where the biophysics of lipid bilayers determines either the dynamics of the system or the mechanical equilibrium state of the cell membrane.

First, we will examine the dynamic response of cell-sized lipid vesicles exposed to solute imbalance. Based on experimental observations that giant vesicles in hypotonic condition exhibit a non-intuitive pulsatile behavior characterized by swell-burst cycles, we will present a theoretical description of the system in the form of coupled stochastic differential equations. We will show how thermal fluctuations enable stochastic pore nucleation, leading to a dependence of the lytic strain on the load rate, and unravel scaling relationships between the pulsatile dynamics and the vesicle properties. We will then extend this framework to account for surface stressors, and show how distinct pore dynamics can be reached in lipid vesicles undergoing solubilization or photooxidation.

In the second part of the talk we will turn our attention to specific membrane morphologies observed in the cellular environments, and propose a theoretical approach to compute the required distribution of protein-induced curvature that sustains a given membrane structure at mechanical equilibrium. We will investigating the role of spontaneous curvature in minimal surfaces, which include catenoids — relevant to vesicle trafficking, tubulation, and nuclear pores — and helicoids  — relevant to endoplasmic reticulum ramps. Importantly we will show the existence of energy barriers associated with geometrical variations of the membrane structure, pointing out the need for a coordinated action of at least two distinct curvature-inducing proteins, in agreement with experimental observations of budding processes.

Wednesday September 26 at 12:00pm in room 646A