Conformation of receptor‐bound arrestin‐1: a site‐directed spin labeling study

Arrestin‐1 binds to light‐activated phosphorylated rhodopsin (P‐Rh*) to terminate G‐protein signaling. To map conformational changes upon binding to the receptor, spin labels were introduced pairwise in arrestin and Double Electron‐Electron Resonance (DEER) was used to monitor interspin distance changes. Of particular interest was to test a “clam shell” model wherein the N and C terminal domains close upon the receptor binding. Based on global distance mapping, the following features were revealed: (1) the relative positions of the N and C domains remain largely unchanged, contrary to expectations of the clam shell model; (2) a loop implicated in the P‐Rh*‐arrestin interaction (the “finger loop”, residues 60–80) moves toward the binding cavity of P‐Rh*, but less than required to extend fully into the binding cleft on P‐Rh*; (3) a striking and unanticipated movement of a loop containing residue 139 away from the adjacent finger loop, takes place perhaps to facilitate P‐Rh* interaction with finger loop itself; (4) a loop in the C domain containing residue 344 moves toward the receptor. A model based on this data provides the first description of the active receptor‐bound state of arrestin. NIH grants EY011500, GM077561, GM081756 (VVG), EY05216 and the Jules Stein Professorship Endowment (WLH)