An improved tripod amphiphile for membrane protein solubilization

Intrinsic membrane proteins represent a large fraction of the proteins prod uced by living organisms and perform many crucial functions. Structural and functional characterization of membrane proteins generally requires that t hey be extracted from the native lipid bilayer and solubilized with a small synthetic amphiphile, for example, a detergent. We describe the developmen t of a small molecule with a distinctive amphiphilic architecture, a "tripo d amphiphile," that solubilizes both bacteriorhodopsin (BR) and bovine rhod opsin (Rho). The polar portion of this amphiphile contains an amide and an amine-oxide: small variations in this polar segment are found to have profo und effects on protein solubilization properties. The optimal tripod amphip hile extracts both BR and Rho from the native membrane environments and mai ntains each protein in a monomeric native-like form for several weeks after delipidation. Tripod amphiphiles are designed to display greater conformat ional rigidity than conventional detergents, with the long-range goal of pr omoting membrane protein crystallization. The results reported here represe nt an important step toward that ultimate goal.