Discrete Supported Bilayer Patches to Interrogate Membrane Protein Advection, Phase Separation, and Bilayer-Surface Coupling

Abstract

Experimentalists studying membrane biophysics find that supported lipid bilayers (SLBs) possess several convenient advantages over vesicles: they are flat, stable over time, and can be patterned with immobile domains of fluid phases. However, they differ from vesicle membranes in that individual lipid dynamics are slower, and collective lipid flow is prevented entirely. Despite these changes, SLBs are particularly suitable for studying membrane protein binding and advection by flow [1, 2]. We prepare supported bilayers formed from individual GUVs to investigate the mechanical details of membrane coupling to thier glass support. We previously observed that proximity to the support increases in the temperature at which phase-separated membranes appear homogeneous by fluorescence microscopy, and can prevent some transitions entirely [3]. We continue to investigate membrane-glass coupling by quantifying the response of glass-supported membranes to changes in pressure. We observe a reversible expansion of membrane area by about 10% when pressure is increased, and describe the dynamics of this response. We show how this expansion varies with membrane composition and with the roughness of the glass surface. Finally, we investigate flow-mediated lateral transport of membrane-anchored proteins across the surface of SLB patches, measuring the ratio of advection to diffusion in order to define a protein mobility relative to the stationary membrane. [1] Shu-Kai Hu, Ling-Ting Huang and Ling Chao. Membrane species mobility under in-lipid-membrane forced convection. Soft Matter, 2016, 12, 6954 [2] Peter Jönsson, Anders Gunnarsson, and Fredrik Höök. Accumulation and Separation of Membrane-Bound Proteins Using Hydrodynamic Forces. Analytical Chemistry, 2011, 83, 604-611 [3] Ross Gunderson and Aurelia Honerkamp-Smith. Liquid-liquid phase transition temperatures increase when lipid bilayers are supported on glass. Biophysica et Biochimica Acta - Biomembranes 1860 (10), 1965-1971 (2018)