Elastic properties of polyunsaturated phosphatidylethanolamines influence rhodopsin function

Abstract

Membranes with a high content of polyunsaturated phosphatidylethanolamines (PE) facilitate formation of metarhodopsin-II (M_II), the photointermediate of bovine rhodopsin that activates the G protein transducin. We determined whether M_II-formation is quantitatively linked to the elastic properties of PEs. Curvature elasticity of monolayers of the polyunsaturated lipids 18 : 0–22 : 6_n − 3PE, 18 : 0–22 : 5_n − 6PE and the model lipid 18 : 1_n − 9–18 : 1_n − 9PE were investigated in the inverse hexagonal phase. All three lipids form lipid monolayers with rather low spontaneous radii of curvature of 26–28 Å. In membranes, all three PEs generate high negative curvature elastic stress that shifts the equilibrium of M_I/M_II photointermediates of rhodopsin towards M_II formation.