The cannabinoid receptor 1 (CB1) is the principal target of the psychoactive constituent of marijuana, the partial agonist Δ9-tetrahydrocannabinol (Δ9-THC)1. Here we report two agonist-bound crystal structures of human CB1 in complex with a tetrahydrocannabinol (AM11542) and a hexahydrocannabinol (AM841) at 2.80 Å and 2.95 Å resolution, respectively. The two CB1–agonist complexes reveal important conformational changes in the overall structure, relative to the antagonist-bound state2, 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 Phe2003.36 and Trp3566.48 (superscripts denote Ballesteros–Weinstein numbering3) is experimentally observed and appears to be essential for receptor activation. The structures reveal important insights into the activation mechanism of CB1 and provide a molecular basis for predicting the binding modes of Δ9-THC, and endogenous and synthetic cannabinoids. The plasticity of the binding pocket of CB1 seems to be a common feature among certain class A G-protein-coupled receptors. These findings should inspire the design of chemically diverse ligands with distinct pharmacological properties.

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.

Graphical AbstractHighlights d Crystal structure of human CB2 in complex with antagonist AM10257 is determined d A high degree of conformational similarity with the agonistbound CB1 is uncovered d The yin-yang relationship of CB2 and CB1 will facilitate the design of selective drugs In BriefThe structure of the human cannabinoid receptor CB2 reveals how small molecules affect CB2 differently than CB1 and point to principles that could inform rational and selective drug design. SUMMARYThe cannabinoid receptor CB2 is predominately expressed in the immune system, and selective modulation of CB2 without the psychoactivity of CB1 has therapeutic potential in inflammatory, fibrotic, and neurodegenerative diseases. Here, we report the crystal structure of human CB2 in complex with a rationally designed antagonist, AM10257, at 2.8 Å resolution. The CB2-AM10257 structure reveals a distinctly different binding pose compared with CB1. However, the extracellular portion of the antagonist-bound CB2 shares a high degree of conformational similarity with the agonist-bound CB1, which led to the discovery of AM10257's unexpected opposing functional profile of CB2 antagonism versus CB1 agonism. Further structural analysis using mutagenesis studies and molecular docking revealed the molecular basis of their function and selectivity for CB2 and CB1. Additional analyses of our designed antagonist and agonist pairs provide important insight into the activation mechanism of CB2. The present findings should facilitate rational drug design toward precise modulation of the endocannabinoid system.

Drugs frequently require interactions with multiple targets-via a process known as polypharmacology-to achieve their therapeutic actions. Currently, drugs targeting several serotonin receptors, including the 5-HT receptor, are useful for treating obesity, drug abuse, and schizophrenia. The competing challenges of developing selective 5-HT receptor ligands or creating drugs with a defined polypharmacological profile, especially aimed at G protein-coupled receptors (GPCRs), remain extremely difficult. Here, we solved two structures of the 5-HT receptor in complex with the highly promiscuous agonist ergotamine and the 5-HT receptor-selective inverse agonist ritanserin at resolutions of 3.0 Å and 2.7 Å, respectively. We analyzed their respective binding poses to provide mechanistic insights into their receptor recognition and opposing pharmacological actions. This study investigates the structural basis of polypharmacology at canonical GPCRs and illustrates how understanding characteristic patterns of ligand-receptor interaction and activation may ultimately facilitate drug design at multiple GPCRs.

Asparaginyl endopeptidase (AEP) is an endo/lysosomal cysteine endopeptidase with a preference for an asparagine residue at the P1 site and plays an important role in the maturation of toll-like receptors 3/7/9. AEP is known to undergo autoproteolytic maturation at acidic pH for catalytic activation. Here, we describe crystal structures of the AEP proenzyme and the mature forms of AEP. Structural comparisons between AEP and caspases revealed similarities in the composition of key residues and in the catalytic mechanism. Mutagenesis studies identified N44, R46, H150, E189, C191, S217/S218 and D233 as residues that are essential for the cleavage of the peptide substrate. During maturation, autoproteolytic cleavage of AEP's cap domain opens up access to the active site on the core domain. Unexpectedly, an intermediate autoproteolytic maturation stage was discovered at approximately pH 4.5 in which the partially activated AEP could be reversed back to its proenzyme form. This unique feature was confirmed by the crystal structure of AEP pH4.5 (AEP was matured at pH 4.5 and crystallized at pH 8.5), in which the broken peptide bonds were religated and the structure was transformed back to its proenzyme form. Additionally, the AEP inhibitor cystatin C could be digested by the fully activated AEP, but could not be digested by activated cathepsins. Thus, we demonstrate for the first time that cystatins may regulate the activity of AEP through substrate competition for the active site.

No abstract

Water table drawdown across peatlands increases carbon dioxide (CO 2 ) and reduces methane (CH 4 ) emissions. The net climatic effect remains unclear. Based on observations from 130 sites around the globe, we found a positive (warming) net climate effect of water table drawdown.Using a machine-learning based upscaling approach, we predict that peatland water table drawdown driven by climate drying and human activities will increase CO 2 emissions by 1.13 (95% interval: 0.88 -1.50 ) Gt yr -1 and reduce CH 4 by 0.26 (0.14 -0.52) Gt CO 2 -eq yr -1 , resulting in a net increase of greenhouse gas (GHG) of 0.86 (0.36 -1.36) Gt CO 2 -eq yr -1 by the end of the 21 st century under the RCP8.5 climate scenario. This net source drops to 0.73 (0.2 -1.2) Gt CO 2 -eq yr -1 under RCP2.6. Our results point to an urgent need to preserve pristine and rehabilitate drained peatlands to decelerate the positive (more warming) feedback among water table drawdown, increased GHG emissions and climate warming.

Impurity toroidal rotation has been observed in the center of Alcator C-Mod ohmic plasmas from the Doppler shifts of argon and molybdenum x-ray lines. The rotation is highest (~ 6 x 106 cm/s) in the early portion of the discharges, when the loop voltage is highest and the electron density is lowest, and then typically settles to values < 2 x 106 cm/s during the steady state period. The impurity rotation is in the same direction as the electron toroidal drift, opposite to the plasma current, and reverses direction when the plasma current direction is reversed. Molybdenum and argon ions rotate with the same velocity. These observations are in qualitative agreement with neo-classical theory.