title: The solution structure and activation of visual arrestin studied by small-angle X-ray scattering.
abstract: Visual arrestin is converted from a 'basal' state to an 'activated' state by interaction with the phosphorylated C-terminus of photoactivated rhodopsin (R*), but the conformational changes in arrestin that lead to activation are unknown. Small-angle X-ray scattering (SAXS) was used to investigate the solution structure of arrestin and characterize changes attendant upon activation. Wild-type arrestin forms dimers with a dissociation constant of 60 micro m. Small conformational changes, consistent with local movements of loops or the mobile N- or C-termini of arrestin, were observed in the presence of a phosphopeptide corresponding to the C-terminus of rhodopsin, and with an R175Q mutant. Because both the phosphopeptide and the R175Q mutation promote binding to unphosphorylated R*, we conclude that arrestin is activated by subtle conformational changes. Most of the arrestin will be in a dimeric state in vivo. Using the arrestin structure as a guide [Hirsch, J.A., Schubert, C., Gurevich, V.V. & Sigler, P.B. (1999) Cell 97, 257-269], we have identified a model for the arrestin dimer that is consistent with our SAXS data. In this model, dimerization is mediated by the C-terminal domain of arrestin, leaving the N-terminal domains free for interaction with phosphorylated R*.
authors.affiliation: Department of Biochemistry, University of Western Ontario, London, Ontario, Canada. bshilton@uwo.ca
authors.forename: Brian H
authors.initials: BH
authors.lastname: Shilton
authors.forename: J Hugh
authors.initials: JH
authors.lastname: McDowell
authors.forename: W Clay
authors.initials: WC
authors.lastname: Smith
authors.forename: Paul A
authors.initials: PA
authors.lastname: Hargrave
mesh_terms: D000595:Amino Acid Sequence; D019393:Arrestin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019281:Dimerization; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D011487:Protein Conformation; D012243:Rhodopsin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012542:Scattering, Radiation; D012996:Solutions; D014965:X-Rays
chemical_list: D019393:Arrestin; D010446:Peptide Fragments; D010750:Phosphoproteins; D012996:Solutions; D012243:Rhodopsin