The effects of protein on lipid organization in a model membrane system: a spin probe and x-ray study.

Abstract

The role of proteins and polypeptides in controlling the orientation of lipid molecules in bilayers was investigated by spin probe and X-ray diffraction techniques. Only when proteins and polypeptides had a net positive charge was a marked effect noted on molecular orientation within brain lipid films. Several proteins and polypeptides exerted an effect similar to that of salts leading to the formation of planar parallel multibilayers with the long axis of the spin probe oriented close to the normal to the plane. Others produced broad angular distributions of the probe within the multilayers. This latter effect took place even in the presence of inorganic ions, which by themselves tend to orient the probes perpendicular to the lamellar plane. The nonpolar residues of the polypeptides are thought to produce disorder by interdigitating with the lipids.