The 2.8 angstrom crystal structure of visual arrestin: A model for arrestin's regulation

G protein-coupled signaling is utilized by a wide variety of eukaryotes for communicating information from the extracellular environment. Signal termi nation is achieved by the action of the arrestins, which bind to activated, phosphorylated G protein-coupled receptors. We describe here crystallograp hic studies of visual arrestin in its basal conformation. The salient featu res of the structure are a bipartite molecule with an unusual polar core. T his core is stabilized in part by an extended carboxy-terminal tail that lo cks the molecule into an inactive state. In addition, arrestin is found to be a dimer of two asymmetric molecules, suggesting an intrinsic conformatio nal plasticity. In conjunction with biochemical and mutagenesis data, we pr opose a molecular mechanism by which arrestin is activated for receptor bin ding.