Abstract
Non-visual arrestins interact with hundreds of different G protein-coupled receptors (GPCRs). Here we show that by introducing mutations into elements that directly bind receptors, the specificity of arrestin-3 can be altered. Several mutations in the two parts of the central "crest" of the arrestin molecule, middle-loop and C-loop, enhanced or reduced arrestin-3 interactions with several GPCRs in receptor subtype and functional state-specific manner. For example, the Lys139Ile substitution in the middle-loop dramatically enhanced the binding to inactive M2 muscarinic receptor, so that agonist activation of the M2 did not further increase arrestin-3 binding. Thus, the Lys139Ile mutation made arrestin-3 essentially an activation-independent binding partner of M2, whereas its interactions with other receptors, including the β2-adrenergic receptor and the D1 and D2 dopamine receptors, retained normal activation dependence. In contrast, the Ala248Val mutation enhanced agonist-induced arrestin-3 binding to the β2-adrenergic and D2 dopamine receptors, while reducing its interaction with the D1 dopamine receptor. These mutations represent the first example of altering arrestin specificity via enhancement of the arrestin-receptor interactions rather than selective reduction of the binding to certain subtypes.