Mechanical Properties of Giant Plasma Membrane Vesicles

Abstract

Giant unilamellar vesicles are a popular membrane model because of their accessibility to many experimental methods. While the ability to precisely control the composition of such membranes is advantageous for basic physicochemical characterization of lipid membranes and their interactions, artificially formed GUVs suffer from some limitations. Only membranes of low compositional complexity, low protein densities and random protein orientation in the bilayer can be obtained. In contrast, the plasma membrane of the living cell is highly complex in composition, crowded with proteins which have a defined orientation. As a missing link between these two extremes, chemically lysed plasma membrane vesicles have recently raised renewed interest. These vesicles, also called giant plasma membrane vesicles (GPMVs), have attracted attention because of their ability to exhibit optically resolvable liquid-liquid phase separation with micron-sized domains the formation of which is suppressed in the plasma membrane. In this work, we study the mechanical properties of GPMVs. We compare how various isolation conditions, such as chemical composition of solutions used to derive GPMVs, cell densities and cholesterol content, influence their bending rigidity. We also investigate how the local cellular environment modules the mechanical properties of extracted GPMVs. Furthermore, we measure the GPMV bending rigidity as a function of temperature and assess their phase state. Using micropipette aspiration we find a surprisingly large amount of hidden area which can be easily pulled out. We investigate the source and mechanism by which these area reservoirs appear. With these measurements, we hope to contribute to the understanding of the mechanical properties of the native plasma membrane. This work is part of the MaxSynBio consortium which is jointly funded by the Federal Ministry of Education and Research of Germany and the Max Planck Society.