CHANNEL-FORMING PEPTIDES IN UNIFORMLY ALIGNED MULTILAYERS OF MEMBRANES

We describe one new method of ultraviolet circular dichroism (CD) and one improved method of X-ray lamellar diffraction for obtaining structural data of membrane proteins. Both methods employ samples of uniformly aligned multilayers of membranes. It was proved earlier that a CD band of ct helices is polarized along the helix axis. Because membrane proteins often contain alpha-helical sections, measurement of CD at the normal and oblique incident angles relative to the plane of the membrane reveals the orientation of the protein molecules. This method of oriented CD is used to study a long-standing problem. of alamethicin; that is, how does the amphipathic helical peptide associate with a membrane? Our investigation led to the discovery of a new phenomenon of cooperative peptide insertion in bilayer lipid membranes. We next describe a method of high-resolution lamellar diffraction that was used to reveal the location of the monovalent and divalent ion binding sites in the gramicidin channel.