The High-Resolution Structure of Activated Opsin Reveals a Conserved Solvent Network in the Transmembrane Region Essential for Activation

Abstract

Rhodopsin, a light-activated G protein coupled receptor (GPCR), has been the subject of numerous biochemical and structural investigations, serving as a model receptor for GPCRs and their activation. Herein we present the 2.3 Å resolution structure of native-source rhodopsin stabilized in a conformation competent for G protein binding. An extensive water-mediated hydrogen bond network linking the chromophore binding site to the site of G protein binding is observed, providing connections to conserved motifs essential for GPCR activation. Comparison of this extensive solvent mediated hydrogen-bonding network to the positions of ordered solvent in earlier crystallographic structures of rhodopsin photointermediates reveals both static structural and dynamic functional water-protein interactions present during the activation process. When taken with observations that solvent occupies similar positions in the structures of other GPCRs, these analyses strongly support an integral role for this dynamic ordered water network in both rhodopsin and GPCR activation.

Structural basis of ligand interaction with atypical chemokine receptor 3

“…The path of ACKR3 residues with agonist-induced increases in oxidation rates is in striking agreement with solvent networks identified in active states of both rhodopsin and opioid receptors (Fig. 8b)4143. Previous radiolytic footprinting studies of GPCRs have shown that higher oxidation rates of residues lining this path correlate with an increased population of active receptor conformations both for rhodopsin (photoactivated and transducin-bound (Rho*−G t )>photoactivated (Rho*)>ground state (Rho)) and the serotonin type 4 (5-HT4) receptor (apo>inverse agonist bound)2324 (Fig.…”

“…Many of these residues are buried in the TM domain of the receptor and cannot possibly be exposed to bulk solvent; therefore, their changes in oxidation are due to rearrangement of structured water molecules within the TM domain. Such water molecules are consistently found in several 7TM receptors by X-ray crystallography or structure-based MS experiments233839, and their positions appear to be affected by receptor activation, leading to restructuring of water-mediated polar residue networks404142. The path of ACKR3 residues with agonist-induced increases in oxidation rates is in striking agreement with solvent networks identified in active states of both rhodopsin and opioid receptors (Fig.…”

“…However, the structural basis of biased agonism remains poorly understood, partly because the available crystal structures of G-protein- and β-arrestin complexed GPCRs414647 do not show any pronounced conformational differences in the receptors when compared with each other. The present study adds to the growing body of evidence supporting the similarity of receptor conformational changes that lead to activation of G-protein- versus β-arrestin-mediated pathways.…”

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“…the reorientation of W265 6.48 is consistent with a conformational transition, and the increased solvent accessibility of the intracellular region with opening of a binding cleft to accommodate intracellular effectors (60, 108). Furthermore, the results corroborate the hypothesis of activation being mediated by an extensive water-mediated intramolecular polar network in GPCRs (8, 55). Taken together, these results suggest that although ACKR3 exclusively activates β-arrestin dependent pathways, its active conformation is similar to that of canonical GPCRs.…”

“…3e). Finally, R134 3.50 and L226 were identified as critical by the screen and likely represent G protein interaction hotspots as their coupling role is conserved across several GPCRs (8, 108) (Fig. 3f).…”