Crystal Structure of the Human Cannabinoid Receptor CB1

Abstract

SUMMARY Cannabinoid receptor 1 (CB1) is the principal target of Δ9-tetrahydrocannabinol (THC), a psychoactive chemical from Cannabis sativa with a wide range of therapeutic applications and a long history of recreational use. CB1 is activated by endocannabinoids, and is a promising therapeutic target for pain management, inflammation, obesity and substance abuse disorders. Here, we present the 2.8 Å crystal structure of human CB1 in complex with AM6538, a stabilizing antagonist, synthesized and characterized for this structural study. The structure of the CB1-AM6538 complex reveals key features of the receptor and critical interactions for antagonist binding. In combination with functional studies and molecular modeling, the structure provides insight into the binding mode of naturally occurring CB1 ligands, such as THC, and synthetic cannabinoids. This enhances our understanding of the molecular basis for the physiological functions of CB1 and provides new opportunities for the design of next-generation CB1-targeting pharmaceuticals.

Crystal structures of agonist-bound human cannabinoid receptor CB1

“…5j) adopt a C-shaped conformation and their long tails extend into the long channel. In comparison with other lipid receptors, such as sphingosine-1-phosphate receptor 1 (S1P 1 ), the alkyl chain of AM11542 and AM841 occupies a similar position as in ‘arm 2’ of the antagonist AM6538 2 , as well as the alkyl chain of ML056 in the S1P 1 receptor 15 (Fig. 3b), indicating that this could be a conserved binding pocket for alkyl chains within lipid-binding receptors.…”

“…Here we report two agonist-bound crystal structures of human CB 1 in complex with a tetrahydrocannabinol (AM11542) and a hexahydrocannabinol (AM841) at 2.80 Å and 2.95 Å resolution, respectively. The two CB 1 –agonist complexes reveal important conformational changes in the overall structure, relative to the antagonist-bound state 2 , including a 53% reduction in the volume of the ligand-binding pocket and an increase in the surface area of the G-protein-binding region. In addition, a ‘twin toggle switch’ of Phe200 3.36 and Trp356 6.48 (superscripts denote Ballesteros–Weinstein numbering 3 ) is experimentally observed and appears to be essential for receptor activation.…”

“…The principal Cannabis constituent, Δ 9 -THC, exerts its psychotropic effects by activating CB 1 , which is also the primary target of the endocannabinoids, anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) 1,6 . Structural examination of CB 1 in complex with the antagonist AM6538 2 and taranabant 7 provides molecular insights into the inactive state of the receptor, yet does not inform us as to how CB 1 elicits its diverse physiological effects.…”

“…The two agonist-bound CB 1 structures were determined using a thermostabilizing construct as previously described 2 for CB 1 –AM6538 (Extended Data Fig. 2, Extended Data Table 1).…”

“…This is the largest structural change, especially within the extracellular portion, observed in the solved agonist/antagonist-bound pairs of class A G-protein-coupled receptors (GPCRs) (Extended Data Table 3). Consequently, owing to the inward shifts of helices I/II, and the subsequent inward rotation of the side chains of Phe170 2.57 and Phe174 2.61 that occupy the gap pocket 2 (Fig. 3b), the volume of the ligand-binding pocket shrinks from 822 Å 3 in the antagonist-bound structure to 384 Å 3 in the agonist-bound complex, representing a 53% reduction (Fig.…”