title: Crystal structure of pre-activated arrestin p44.
abstract: Arrestins interact with G-protein-coupled receptors (GPCRs) to block interaction with G proteins and initiate G-protein-independent signalling. Arrestins have a bi-lobed structure that is stabilized by a long carboxy-terminal tail (C-tail), and displacement of the C-tail by receptor-attached phosphates activates arrestins for binding active GPCRs. Structures of the inactive state of arrestin are available, but it is not known how C-tail displacement activates arrestin for receptor coupling. Here we present a 3.0 Å crystal structure of the bovine arrestin-1 splice variant p44, in which the activation step is mimicked by C-tail truncation. The structure of this pre-activated arrestin is profoundly different from the basal state and gives insight into the activation mechanism. p44 displays breakage of the central polar core and other interlobe hydrogen-bond networks, leading to a ∼21° rotation of the two lobes as compared to basal arrestin-1. Rearrangements in key receptor-binding loops in the central crest region include the finger loop, loop 139 (refs 8, 10, 11) and the sequence Asp 296-Asn 305 (or gate loop), here identified as controlling the polar core. We verified the role of these conformational alterations in arrestin activation and receptor binding by site-directed fluorescence spectroscopy. The data indicate a mechanism for arrestin activation in which C-tail displacement releases critical central-crest loops from restricted to extended receptor-interacting conformations. In parallel, increased flexibility between the two lobes facilitates a proper fitting of arrestin to the active receptor surface. Our results provide a snapshot of an arrestin ready to bind the active receptor, and give an insight into the role of naturally occurring truncated arrestins in the visual system.
authors.affiliation: Institut für Medizinische Physik und Biophysik (CC2), Charité-Universitätsmedizin Berlin, Charitéplatz 1, D-10117 Berlin, Germany.
authors.forename: Yong Ju
authors.initials: YJ
authors.lastname: Kim
authors.forename: Klaus Peter
authors.initials: KP
authors.lastname: Hofmann
authors.forename: Oliver P
authors.initials: OP
authors.lastname: Ernst
authors.forename: Patrick
authors.initials: P
authors.lastname: Scheerer
authors.forename: Hui-Woog
authors.initials: HW
authors.lastname: Choe
authors.forename: Martha E
authors.initials: ME
authors.lastname: Sommer
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D019390:Arrestins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008970:Molecular Weight; D011487:Protein Conformation; D020033:Protein Isoforms / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D012399:Rotation; D017384:Sequence Deletion; D055672:Static Electricity; D000071557:beta-Arrestins
chemical_list: D019390:Arrestins; D020033:Protein Isoforms; D000071557:beta-Arrestins