X-RAY CRYSTAL-STRUCTURE OF ARRESTIN FROM BOVINE ROD OUTER SEGMENTS

Retinal arrestin is the essential protein for the termination of the l ight response in vertebrate rod outer segments. It plays an important role in quenching the light-induced enzyme cascade by its ability to b ind to phosphorylated light-activated rhodopsin (P-Rh). Arrestins are found in various G-protein-coupled amplification cascades. Here we re port on the three-dimensional structure of bovine arrestin (relative m olecular mass, 45,300) at 3.3 Angstrom resolution. The crystal structu re comprises two domains of antiparallel beta-sheets connected through a hinge region and one short alpha-helix on the back of the amino-ter minal fold. The binding region for phosphorylated light-activated rhod opsin is located at the N-terminal domain, as indicated by the docking of the photoreceptor to the three-dimensional structure of arrestin. This ag rees with the interpretation of binding studies on partially d igested and mutated arrestin.