Membrane protein conformational changes—involving folding, stability, and membrane shape transitions—potentially involve elastic remodeling of the lipid bilayer. Evidence suggests that membrane lipids affect proteins through relatively long-range interactions, extending beyond a single annulus of next-neighbor boundary lipids. Application of the theory of elasticity, derived from classical physics, explains the polymorphism of both detergents and membrane phospholipids. A flexible surface model (FSM) describes the balance of curvature and hydrophobic forces in lipid-protein interactions. Chemically nonspecific properties of the lipid bilayer modulate conformational energetics of membrane proteins. The new biomembrane model challenges the standard fluid mosaic model found in biochemistry texts. Influences of bilayer thickness, nonlamellar-forming lipids, detergents, and osmotic stress are all explained by the FSM. According to the FSM, geometrical deformation of the lipids adjacent to the protein to match the spontaneous (intrinsic) monolayer curvature counterbalances the unfavorable hydrophobic mismatch. Membrane curvature elasticity and concepts of a flexible surface and minimal surfaces were formulated by Helfrich and have found widespread application in the field of surfactant and membrane nanotechnology. Similar concepts are applicable to biomembranes, where membrane stress fields govern energetics of protein conformations due to their different shapes within the bilayer. As an example, rhodopsin activation is known to be promoted by nonlamellar-forming lipids characterized by small headgroups and polyunsaturated acyl chains. Upon light absorption, rhodopsin becomes a sensor of the negative spontaneous curvature of the membrane. If the monolayer tends to curve towards water, then an elastic two-way coupling of the protein to local monolayer curvature can occur. Increased awareness of curvature forces closely links structural biology to lipid physical chemistry to explain biomembrane structure and function.

Flexible surface model for lipid-protein interactions

2019 Spring National Meeting

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