The solution structure and activation of visual arrestin studied by smallâangle Xâray scattering
2002
Shilton, Brian H. | McDowell, J Hugh | Smith, W Clay | Hargrave, Paul A.
Visual arrestin is converted from a ‘basal’ state to an ‘activated’ state by interaction with the phosphorylated Câterminus of photoactivated rhodopsin (R*), but the conformational changes in arrestin that lead to activation are unknown. Smallâangle Xâray scattering (SAXS) was used to investigate the solution structure of arrestin and characterize changes attendant upon activation. Wildâtype arrestin forms dimers with a dissociation constant of 60âµm. Small conformational changes, consistent with local movements of loops or the mobile Nâ or Câtermini of arrestin, were observed in the presence of a phosphopeptide corresponding to the Câterminus 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,â257–269], we have identified a model for the arrestin dimer that is consistent with our SAXS data. In this model, dimerization is mediated by the Câterminal domain of arrestin, leaving the Nâterminal domains free for interaction with phosphorylated R*.
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