Arrestins (abbreviated Arr) are a small family of proteins important for regulating signal transduction at G protein-coupled receptors.

[7][8][9][10][6] In addition to GPCRs, arrestins bind to other classes of cell surface receptors and a variety of other signaling proteins.

The proto-chordate Ciona intestinalis (sea squirt) has only one arrestin, which serves as visual in its mobile larva with highly developed eyes, and becomes generic non-visual in the blind sessile adult.

Subsequently, the receptor could be either directed to degradation compartments (lysosomes) or recycled back to the plasma membrane where it can again signal.

Arrestins also bind microtubules (part of the cellular skeleton), where they assume yet another conformation, different from both free and receptor-bound form.

Their nuclear functions are not fully understood, but it was shown that all four mammalian arrestin subtypes remove some of their partners, such as protein kinase JNK3 or the ubiquitin ligase Mdm2, from the nucleus.

Important serine (Ser) and threonine (Thr) residues in rhodopsin's tail, particularly Thr-340 and Ser-343, are phosphorylated by enzymes called GRKs.

These phosphorylated residues strongly attract arrestin, helping it bind tightly and effectively shut down rhodopsin’s signaling[15].

This interaction, clearly seen in the crystal structure (PDB ID: 4ZWJ), shows how arrestin fits precisely onto activated and phosphorylated rhodopsin, efficiently stopping the visual signal [16].