Intrinsic membrane proteins represent a large fraction
of the proteins produced by living organisms and perform
many crucial functions. Structural and functional characterization
of membrane proteins generally requires that they be extracted
from the native lipid bilayer and solubilized with a small
synthetic amphiphile, for example, a detergent. We describe
the development of a small molecule with a distinctive
amphiphilic architecture, a “tripod amphiphile,”
that solubilizes both bacteriorhodopsin (BR) and bovine
rhodopsin (Rho). The polar portion of this amphiphile contains
an amide and an amine-oxide; small variations in this polar
segment are found to have profound effects on protein solubilization
properties. The optimal tripod amphiphile extracts both
BR and Rho from the native membrane environments and maintains
each protein in a monomeric native-like form for several
weeks after delipidation. Tripod amphiphiles are designed
to display greater conformational rigidity than conventional
detergents, with the long-range goal of promoting membrane
protein crystallization. The results reported here represent
an important step toward that ultimate goal.