The cannabinoid receptor 1 (CB1) is the most abundantly expressed G-protein-coupled-receptor (GPCR) in the brain1. CB1 is activated by THC, the major psychoactive component of Cannabis. More recently synthetic cannabinoids (SCs) have been designed to target CB1. Both plant-based and SCs piggyback their pharmacology on a collection of endogenous molecules known as the endocannabinoids. Endocannabinoid signalling has proven to play important roles in memory, mood, sleep, appetite, inflammation and pain sensation2. Owing to their involvement in regulating a slew of physiological process, CB1 has been an attractive target for therapeutic development.
Similar to other GPCRs, CB1 elicits its physiological response through heterotrimeric G-proteins with CB1 signalling primarily through the adenylyl-cyclase inhibitory family of G-proteins (Gi/o). Activating CB1 has shown to have anxiolytic, analgesia, neuroprotective and antinausea effects3. However, THC and to a much greater extent SCs induce side-effects which include dependence, seizures, convulsions and psychoses4. Fubinacas, a class of potent synthetic agonists infused in illicit herbal mixes such as “K2” and “Spice”, have been named “zombie drugs” due to their association with users in semi-comatose state5. Although these side-effects and potential lethality limit therapeutic use, such compounds represent important tools to dissect mechanistic questions regarding CB1 activation in order to design drugs with improved properties.
To gain structural insights into the binding and activation of CB1 by SCs, we determined the cryo-EM structure of a Fubinaca-activated full-length CB1-Gi signalling complex. The structure, complemented by molecular dynamics and docking, provides a snapshot into the ligand binding properties, activation of CB1, and the structural basis of G-protein coupling. This study sets the framework to integrate a large body of structure-activity relationship (SAR) studies towards understanding cannabinoid receptor activation by different classes of ligands, and also provides insights into the promiscuous coupling of CB1 to other G-proteins.