Activation and Signaling Mechanism Revealed by Cannabinoid Receptor-Gi Complex Structures

Human endocannabinoid systems modulate multiple physiological processes mainly through the activation of cannabinoid receptors CB1 and CB2. Their high sequence similarity, low agonist selectivity, and lack of activation and G protein-coupling knowledge have hindered the development of therapeutic applications. Importantly, missing structural information has significantly held back the development of promising CB2-selective agonist drugs for treating inflammatory and neuropathic pain without the psychoactivity of CB1. Here, we report the cryoelectron microscopy structures of synthetic cannabinoid-bound CB2 and CB1 in complex with Gi, as well as agonist-bound CB2 crystal structure. Of important scientific and therapeutic benefit, our results reveal a diverse activation and signaling mechanism, the structural basis of CB2-selective agonists design, and the unexpected interaction of cholesterol with CB1, suggestive of its endogenous allosteric modulating role. [Display omitted] •3D structures of CB2-AM12033-Gi, CB1-AM841-Gi, and CB2-AM12033 are determined•Structural evidence of G protein selectivity by CB1 and CB2 is identified•MD simulations reveal the distinct binding behavior of HU308 in CB2 and CB1•Cholesterol molecule as an endogenous allosteric modulator of CB1 is uncovered Structure and simulations of cannabinoid receptors CB2 and CB1 in their inactive, active-like, and activated signaling states reveal residue differences that may provide G protein selectivity, the distinct binding behavior of CB2 agonists in CB2 and CB1, as well as evidence for modulation of CB1 by cholesterol binding.