Light-Controlled Lipid Interaction and Membrane Organization in Photolipid Bilayer Vesicles.

Controlling lateral interactions between lipid molecules in a bilayer membrane to guide membrane organization and domain formation is a key factor for studying and emulating membrane functionality in synthetic biological systems. Here, we demonstrate an approach to reversibly control lipid organization, domain formation, and membrane stiffness of phospholipid bilayer membranes using the photoswitchable phospholipid azo-PC. azo-PC contains an azobenzene group in the sn2 acyl chain that undergoes reversible photoisomerization on illumination with UV-A and visible light. We demonstrate that the concentration of the photolipid molecules and also the assembly and disassembly of photolipids into lipid domains can be monitored by UV-vis spectroscopy because of a blue shift induced by photolipid aggregation.

Light-Controlled Membrane Mechanics and Shape Transitions of Photoswitchable Lipid Vesicles.

Giant unilamellar vesicles (GUVs) represent a versatile model system to emulate the fundamental properties and functions associated with the plasma membrane of living cells. Deformability and shape transitions of lipid vesicles are closely linked to the mechanical properties of the bilayer membrane itself and are typically difficult to control under physiological conditions. Here, we developed a protocol to form cell-sized vesicles from an azobenzene-containing phosphatidylcholine (azo-PC), which undergoes photoisomerization on irradiation with UV-A and visible light. Photoswitching within the photolipid vesicles enabled rapid and precise control of the mechanical properties of the membrane. By varying the intensity and dynamics of the optical stimulus, controlled vesicle shape changes such as budding transitions, invagination, pearling, or the formation of membrane tubes were achieved. With this system, we could mimic the morphology changes normally seen in cells, in the absence of any molecular machines associated with the cytoskeleton. Furthermore, we devised a mechanism to utilize photoswitchable lipid membranes for storing mechanical energy and then releasing it on command as locally usable work.