Jules Stein Eye Institute, Department of Ophthalmology, University of California, Los Angeles, CA 90095, USA.
Proc Natl Acad Sci U S A. 2012 Nov 6;109(45):18407-12. doi: 10.1073/pnas.1216304109. Epub 2012 Oct 22.
Arrestin-1 (visual arrestin) binds to light-activated phosphorylated rhodopsin (P-Rh*) to terminate G-protein signaling. To map conformational changes upon binding to the receptor, pairs of spin labels were introduced in arrestin-1 and double electron-electron resonance was used to monitor interspin distance changes upon P-Rh* binding. The results indicate that the relative position of the N and C domains remains largely unchanged, contrary to expectations of a "clam-shell" model. A loop implicated in P-Rh* binding that connects β-strands V and VI (the "finger loop," residues 67-79) moves toward the expected location of P-Rh* in the complex, but does not assume a fully extended conformation. A striking and unexpected movement of a loop containing residue 139 away from the adjacent finger loop is observed, which appears to facilitate P-Rh* binding. This change is accompanied by smaller movements of distal loops containing residues 157 and 344 at the tips of the N and C domains, which correspond to "plastic" regions of arrestin-1 that have distinct conformations in monomers of the crystal tetramer. Remarkably, the loops containing residues 139, 157, and 344 appear to have high flexibility in both free arrestin-1 and the P-Rh*complex.
视蛋白相关蛋白-1（视觉 arrestin）与光激活的磷酸化视紫红质（P-Rh*）结合，以终止 G 蛋白信号转导。为了绘制与受体结合时的构象变化图谱，在 arrestin-1 中引入了一对自旋标记，并使用双电子-电子共振监测 P-Rh结合时的自旋间距离变化。结果表明，N 结构域和 C 结构域的相对位置基本保持不变，这与“蛤壳”模型的预期相反。连接β-链 V 和 VI 的一个与 P-Rh结合有关的环（“指环”，残基 67-79）向复合物中 P-Rh的预期位置移动，但不采用完全伸展的构象。观察到一个包含残基 139 的环远离相邻指环的惊人且意外的运动，这似乎促进了 P-Rh的结合。这种变化伴随着 N 结构域和 C 结构域末端包含残基 157 和 344 的远端环的较小运动，这与 arrestin-1 的“塑性”区域相对应，在晶体四聚体的单体中具有独特的构象。值得注意的是，在游离 arrestin-1 和 P-Rh*复合物中，包含残基 139、157 和 344 的环似乎具有很高的灵活性。
