G-protein-coupled receptors (GPCRs) comprise the largest family of membrane proteins in the human genome and mediate cellular responses to an extensive array of hormones, neurotransmitters and sensory stimuli. Although some crystal structures have been determined for GPCRs, most are for modified forms, showing little basal activity, and are bound to inverse agonists or antagonists. Consequently, these structures correspond to receptors in their inactive states. The visual pigment rhodopsin is the only GPCR for which structures exist that are thought to be in the active state1,2. However, these structures are for the apoprotein, or opsin, form that does not contain the agonist all-trans retinal. Here we present a crystal structure at a resolution of 3 Å for the constitutively active rhodopsin mutant Glu 113 Gln3,4,5 in complex with a peptide derived from the carboxy terminus of the α-subunit of the G protein transducin. The protein is in an active conformation that retains retinal in the binding pocket after photoactivation. Comparison with the structure of ground-state rhodopsin6 suggests how translocation of the retinal β-ionone ring leads to a rotation of transmembrane helix 6, which is the critical conformational change on activation7. A key feature of this conformational change is a reorganization of water-mediated hydrogen-bond networks between the retinal-binding pocket and three of the most conserved GPCR sequence motifs. We thus show how an agonist ligand can activate its GPCR.
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We thank X. Deupi and R. Vogel for discussions and reading of the manuscript. We thank R. Crouch for the kind gift of 11-cis retinal. P. J. Reeves we thank for providing the pACMVtetO vector and the HEK293S-GnTI− cells, and for his advice on creating stable cell lines and tetracycline-inducible expression. We also thank the staff at the macromolecular crystallography beamlines at the European Synchrotron Radiation Facility, the Diamond Light Source and the Swiss Light Source. The work was financially supported by NIH grant EY007965 (to D.D.O.), the Human Frontier Science Project programme grant RG/0052 (to D.D.O. and G.F.X.S.), the European Commission FP6 specific targeted research project LSH-2003-1.1.0-1 (to G.F.X.S.), the Marie Curie Intra European Fellowship MEIF-CT-2006-039171 (to J.S.) and the EMBO long-term fellowship ALTF 198-2006 (to J.S.).
The authors declare no competing financial interests.
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Standfuss, J., Edwards, P., D’Antona, A. et al. The structural basis of agonist-induced activation in constitutively active rhodopsin. Nature 471, 656–660 (2011). https://doi.org/10.1038/nature09795
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