The Functional Role of the Lariat Loop Residues in Arrestin Binding to Gpcrs

Abstract

Lariat loop in all arrestins has an unusual shape and participates in maintaining their basal conformation. It supplies two out of five charges that constitute a critical stabilizing intramolecular interaction, the polar core between the two domains. To determine the functional role of individual lariat loop residues we performed comprehensive site-directed mutagenesis of this element and tested the effects of substitutions on arrestin-1 binding to its preferred target, phosphorylated light-activated rhodopsin, as compared to the unphosphorylated activated form. Out of 34 mutations tested, 24 and 25 affected the binding to phosphorylated and unphosphorylated rhodopsin, respectively. Unexpectedly, manipulation of residues following polar core aspartates reduced selectivity as dramatically as replacing these negatively charged aspartates with positively charged arginine. Thus, numerous lariat loop residues play distinct roles in arrestin-1 binding and its exquisite preference for phosphorylated light-activated rhodopsin.

Keywords: GPCR, desensitization, arrestin, receptor binding, conformational change