Chapter 8 Influence of Nonlamellar-Forming Lipids on Rhodopsin

This chapter summarizes evidence obtained during the 1980s and 1990s that suggests an important role of membrane lipids in the visual process. Bulk material properties of the lipid bilayer, as distinguished from chemically specific lipid-protein interactions, appear to modulate conformational transitions of rhodopsin linked to visual excitation. The presence of nonlamellar-forming lipids in rhodopsin-containing membranes is associated with curvature elastic stress, on account of their proximity to a L,-HII phase boundary. The chapter discusses a flexible surface model based on the Helfrich formulation of the bending energy as a unifying conceptual framework. The curvature free energy concept has proven very useful in interpreting the microstructures and phase behavior of aqueous surfactant and lipid systems. In the planar lamellar phase of membrane bilayers, the curvature free energy due to the presence of nonlamellar-forming lipids is frustrated by the chain stretching energy.