Evidence that membrane curvature distorts the tertiary structure of bacteriorhodopsin

The membrane protein bacteriorhodopsin (bR) can be reconstituted into the membrane of the lipid 1-monoolein (MO). This lipid forms a lyotropic liquid crystalline phase whose membrane has hyperbolic interfacial curvature. Using optical absorption spectroscopy and small angle X-ray scattering we have observed retinal unbinding from bR that is correlated with the degree of membrane interfacial curvature. The evidence suggests that bR is susceptible to membrane induced saddle splay for modest perturbations from equilibrium, but for more extreme distortions becomes stiff and resists membrane induced curvature.