Quantification of Curvature Gradients in Highly Curved Tubular Lipid Bilayers

Abstract

Coupling between membrane shape and composition plays an important role in dynamic life of cellular membranes. It becomes increasingly understood that intrinsic curvature preferences of membrane components, proteins and lipids, provides one of the driving forces for such coupling. However, monitoring curvature-driven sorting of membrane components at physiologically relevant time- and length- scales is a challenging task. Here we propose a new approach for real-time quantification of dynamic gradients of membrane curvature and the associated redistribution of membrane component at nanoscale. This method consists in simultaneous measurements of the electrical conductance and fluorescence of the lumen of lipid nanotubes (NTs). By relating changes in the integral conductance of the NT lumen with those in the axial profile of the fluorescence intensity we obtain the geometrical parameters of the nanotube with 10s of nm precision. Furthermore, by varying the electrical potential applied to the NT membrane we can measure, in real time, changes in the elastic moduli of the NT membrane, e.g. upon adsorption of proteins. For basic lipid compositions, the effective bending rigidity measured here coincides with the published values, while entropy-related correction is evident at high curvature stress.