Visual Arrestin Binding to Rhodopsin: DIVERSE FUNCTIONAL ROLES OF POSITIVELY CHARGED RESIDUES WITHIN THE PHOSPHORYLATION-RECOGNITION REGION OF ARRESTIN

Abstract

Arrestin plays a critical role in quenching phototransduction via its ability to specifically interact with the phosphorylated light-activated form of the visual receptor rhodopsin. In an effort to identify the residues involved in interaction with the phosphorylated C terminus of rhodopsin, we introduced point mutations into a basic region in visual arrestin previously implicated in phosphorylation-recognition (residues 163-189). A total of nine point mutations were made, each substituting a neutral hydrophilic residue for a positively charged Lys, Arg, or His. The functional consequences of these mutations were then analyzed by comparing the binding of full-length and truncated wild-type and mutant arrestin to various functional forms of rhodopsin. These studies demonstrate that Arg-171, Arg-175, and Lys-176 in bovine arrestin play a primary role in phosphate interaction, while Lys-166 and Lys-167 likely play a minor role in phosphate binding. In contrast, Lys-163 and His-179 appear to play a regulatory role, while Arg-182 and Arg-189 are not directly involved in arrestin binding to rhodopsin. Arg-175 also appears to function as a phosphorylation-sensitive trigger since charge neutralization by mutagenesis enables arrestin-R175N to bind to light-activated rhodopsin as well as wild-type arrestin binds to phosphorylated light-activated rhodopsin. The implications of these findings for the sequential multisite binding of arrestin to rhodopsin are discussed.