tailieunhanh - Báo cáo Y học: The solution structure and activation of visual arrestin studied by small-angle X-ray scattering

Visual arrestin is converted from a ÔbasalÕ state to an ÔactivatedÕ 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 lM. 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 | Eur. J. Biochem. 269 3801-3809 2002 FEBS 2002 doi The solution structure and activation of visual arrestin studied by small-angle X-ray scattering Brian H. Shilton1 J. Hugh McDowell2 W. Clay Smith2 and Paul A. Hargrave2 3 1 Department of Biochemistry University of Western Ontario London Ontario Canada departments of Ophthalmology and 3Biochemistry and Molecular Biology University of Florida Gainesville Florida USA 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 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 correspondingto 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 . Schubert C. Gurevich . Sigler . 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 hhe Noei minal dominos Hee lor irnercclinn wihli phosphorylated R . Keywords visual arrestin rhodopsin G-protein coupled receptor signalling small-angle X-ray scattering solution structure. The first event in the visual cycle is activation of rhodopsin by light. Photoactivated rhodopsin R initiates a signal transduction cascade that culminates in membrane .