The CB1 receptor mediates the central nervous system response to cannabinoids, and is a drug target for pain, anxiety and seizures. CB1 also responds to allosteric modulators, which influence cannabinoid binding and efficacy. To understand the mechanism of these compounds, we solved the crystal structure of CB1 with the negative allosteric modulator (NAM) ORG27569 and the agonist CP55940. The structure reveals that the NAM binds to an extrahelical site within the inner leaflet of the membrane, which overlaps with a conserved site of cholesterol interaction in many G protein-coupled receptors (GPCRs). The ternary structure with ORG27569 and CP55940 captures an intermediate state of the receptor, in which aromatic residues at the base of the agonist-binding pocket adopt an inactive conformation despite the large contraction of the orthosteric pocket. The structure illustrates a potential strategy for drug modulation of CB1 and other class A GPCRs.
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Structural data have been deposited in the Protein Data Bank (PDB) with coordinate accession number 6KQI. All other data generated or analyzed during this study are included in this published article (and its supplementary information files) or are available from the corresponding author on reasonable request.
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We thank the staff of the GM/CA-CAT beamline 23ID at the Advanced Photon Source for support during data collection. This project was supported by the Edward Mallinckrodt, Jr. Foundation (Scholar Award to D.M.R.), the Welch Foundation (grant no. I-1770 to D.M.R.) and the National Young Thousand Talents Program of China (to Z.S.). APS is a US Department of Energy Office of Science User Facility operated for the Department of Energy Office of Science by Argonne National Laboratory (no. DE-AC02-06CH11357).
The authors declare no competing interests.
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Shao, Z., Yan, W., Chapman, K. et al. Structure of an allosteric modulator bound to the CB1 cannabinoid receptor. Nat Chem Biol 15, 1199–1205 (2019) doi:10.1038/s41589-019-0387-2