LIPIDIC CUBIC PHASES - A NOVEL CONCEPT FOR THE CRYSTALLIZATION OF MEMBRANE-PROTEINS

Understanding the mechanisms of action of membrane proteins requires t he elucidation of their structures to high resolution, The critical st ep in accomplishing this by x-ray crystallography is the routine avail ability of well-ordered three-dimensional crystals. We have devised a novel, rational approach to meet this goal using quasisolid lipidic cu bic phases. This membrane system, consisting of lipid, water, and prot ein in appropriate proportions, forms a structured transparent, and co mplex three-dimensional lipidic array, which is pervaded by an interco mmunicating aqueous channel system, Such matrices provide nucleation s ites (''seeding'') and support growth by lateral diffusion of protein molecules in the membrane (''feeding''). Bacteriorhodopsin crystals we re obtained from bicontinuous cubic: phases, but not from micellar sys tems, implying a critical role of the continuity of the diffusion spac e (the bilayer) on crystal growth, Hexagonal bacteriorhodopsin crystal s diffracted to 3.7 Angstrom resolution, with a space group P6(3), and unit cell dimensions of a = b = 62 Angstrom, c = 108 Angstrom; alpha = beta = 90 degrees and gamma = 120 degrees.