Arrestins (abbreviated Arr) are a small family of proteins important for regulating signal transduction at G protein-coupled receptors.[2][3] Arrestins were first discovered as a part of a conserved two-step mechanism for regulating the activity of G protein-coupled receptors (GPCRs) in the visual rhodopsin system by Hermann Kühn, Scott Hall, and Ursula Wilden[4] and in the β-adrenergic system by Martin J. Lohse and co-workers.[5][6]