LIPIDIC CUBIC PHASES AS TRANSPARENT, RIGID MATRICES FOR THE DIRECT SPECTROSCOPIC STUDY OF IMMOBILIZED MEMBRANE-PROTEINS

Lipidic cubic phases composed of 1-palmitoyl-sn-glycero-3-phosphocholine and water were used as structured, transparent, rigid matrices in an attempt to develop novel media for simultaneous structural and functional investigations of membrane proteins. Bacteriorhodopsin and melittin, immobilized in the cubic phase, resulted in very stable materials, whose circular dichroism (CD) spectra exhibit contents of alpha-helicity akin to those expected from the crystal structures. As judged from CD, the native conformations were temperature independent in the range of existence of the cubic phase (0-50-degrees-C). Addition of NaCl to the bacteriorhodopsin-containing cubic phase stabilized the binding of retinal to the immobilized protein. Without added salt, a slow (i.e., days long) dissociation of retinal at ambient conditions was observed, which however takes place without impairing the native protein's conformation.