Structure and self-association of Arrestin-1

Arrestins halt cell signaling by binding to phosphorylated activated G protein-coupled receptors. Arrestin-1 binds to rhodopsin, arrestin-4 binds to cone opsins, and arrestins-2,3 bind to the rest of GPCRs. In addition, it has been reported that arrestin-1 is functionally expressed in mouse cone photoreceptors. The structural characterization of arrestins was spearheaded by the elucidation of the crystal structure of bovine arrestin-1. Further progress in arrestin structural biology showed that the general fold of the four vertebrate arrestin subtypes is conserved and that self-association seems to play important physiological roles. In solution, mammalian arrestin-1 has been proposed to exist in a species-dependent equilibrium between monomers, dimers, and tetramers, the activated monomer being the form that binds to photo-activated phosphorylated rhodopsin. However, the nature and function of the oligomers of the different arrestin subtypes are still under debate. This article reviews several structural aspects of arrestin-1 in light of two recent crystal structures of Xenopus arrestin-1, which have provided insights on the structure, self-association, activation, and evolution of arrestins in general, and of arrestin-1 in particular.