Hypothesis: The attractive interaction between a cationic surfactant monolayer at the air-water interface and vesicles, incorporating anionic lipids, is sufficient to drive the adsorption and deformation of the vesicles. Osmotic rupture of the vesicles produces a continuous lipid bilayer beneath the monolayer. Experimental: Specular neutron reflectivity has been measured from the surface of a purpose-built laminar flow trough, which allows for rapid adsorption of vesicles, the changes in salt concentration required for osmotic rupture of the adsorbed vesicles into a bilayer, and for neutron contrast variation of the sub-phase without disturbing the monolayer. Findings: The neutron reflectivity profiles measured after vesicle addition are consistent with the adsorption and flattening of the vesicles beneath the monolayer. An increase in the buffer salt concentration results in further flattening and fusion of the adsorbed vesicles, which are ruptured by a subsequent decrease in the salt concentration. This process results in a continuous, high coverage, bilayer suspended 11A beneath the monolayer. As the bilayer is not constrained by a solid substrate, this new mimetic is well-suited to studying the structure of lipid bilayers that include transmembrane proteins.
We present a reliable method of forming a fluid phase lipid bilayer suspended underneath a surfactant monolayer at the air-water interface, a novel bacterial membrane mimic. Bilayer formation proceeds by vesicle adsorption and subsequent rupture beneath a monolayer of a cationic surfactant adsorbed at the air-water interface of a laminar ow trough. The laminar flow facilitates buffer exchange beneath the surfactant monolayer, allowing for sequential deposition of vesicles, osmotic rupture and sub-phase contrast variation for neutron reflectometry. As the lipid bilayer formed by this process does not interact with a solid substrate, the suspended bilayer platform is well-suited to studying lipid bilayers including inserted membrane proteins.
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