Conformational aspects of rhodopsin and retinal disc membranes

Abstract

Abstract We have used two experimental approaches – fluorescence spectroscopy and lectin binding – to obtain information about the structure of rhodopsin and its position in retinal disc membranes. Energy transfer was used as a spectroscopic ruler to deduce proximity relationships in rhodopsin and in disc membranes. Concanavalin A and wheat germ agglutinin served as specific macromolecular probes of the accessibility of the carbohydrate unit of rhodopsin in disc membranes. We infer from these studies that: (1) The rhodopsin molecule is at least 75 Å long and has an elongated shape. (2) There may be distinct hydrophobic and hydrophobic and hydrophilic domains in rhodopsin. (3) The carbohydrate moiety of rhodopsin is on the surface of the disc membrane, probably only on the external face. (4) The disc membrane has an asymmetric structure. (5) The external surface of the disc membrane is closer to site A (a sulfhydryl residue on rhodopsin) than to 11–cis retinal.