Cannabinoid CB(1) receptor ligand binding and function examined through mutagenesis studies of F200 and S383

GPCR Signaling: A Study of the Interplay Between Structure, Energy, and Function

G protein-coupled receptors (GPCRs) exemplify sophisticated allosteric communication, transducing extracellular signals through ligand-induced structural rearrangements that resonate through the molecular scaffold. Despite extensive study, the biophysical underpinnings of how conformational changes spread remain unclear. This work employs a novel physics-based framework to characterize the role of energy dissipation in directing intramolecular signaling pathways. By modeling each residue as a network of coupled oscillators, we generate a localization landscape depicting the vibrational energy distribution throughout the protein scaffold. Quantifying directional energy flux between residues reveals distinct pathways for energy and information transfer, illuminating sequences of allosteric communication. Our analysis of CB1 and CCR5 crystal structures unveils an anisotropic pattern of energy dissipation aligning with key functional dynamics, such as activation-related conformational changes. These anisotropic patterns of vibrational energy flow constitute pre-configured channels for allosteric signaling. Elucidating the relationship between structural topology and energy dissipation patterns provides key insights into the thermodynamic drivers of conformational signaling. This methodology significantly advances our mechanistic understanding of allostery in GPCRs and presents a broadly applicable approach for rationally dissecting allosteric communication pathways, with potential implications for structure-based drug design targeting these critical receptors.

Characterization of binding kinetics and intracellular signaling of new psychoactive substances targeting cannabinoid receptor using transition-based reweighting method

New psychoactive substances (NPS) targeting cannabinoid receptor 1 pose a significant threat to society as recreational abusive drugs that have pronounced physiological side effects. These greater adverse effects compared to classical cannabinoids have been linked to the higher downstream β-arrestin signaling. Thus, understanding the mechanism of differential signaling will reveal important structure-activity relationship essential for identifying and potentially regulating NPS molecules. In this study, we simulate the slow (un)binding process of NPS MDMB-Fubinaca and classical cannabinoid HU-210 from CB1 using multi-ensemble simulation to decipher the effects of ligand binding dynamics on downstream signaling. The transition-based reweighing method is used for the estimation of transition rates and underlying thermodynamics of (un)binding processes of ligands with nanomolar affinities. Our analyses reveal major interaction differences with transmembrane TM7 between NPS and classical cannabinoids. A variational autoencoder-based approach, neural relational inference (NRI), is applied to assess the allosteric effects on intracellular regions attributable to variations in binding pocket interactions. NRI analysis indicate a heightened level of allosteric control of NPxxY motif for NPS-bound receptors, which contributes to the higher probability of formation of a crucial triad interaction (Y7.53-Y5.58-T3.46) necessary for stronger β-arrestin signaling. Hence, in this work, MD simulation, data-driven statistical methods, and deep learning point out the structural basis for the heightened physiological side effects associated with NPS, contributing to efforts aimed at mitigating their public health impact.

Structural and functional insights into the G protein-coupled receptors: CB1 and CB2

The cannabinoid receptors CB1 and CB2 mediate a variety of physiological processes and continue to be explored as desirable drug targets. Both receptors are activated by the endogenous endocannabinoids and the psychoactive components of marijuana. Over the years, many efforts have been made to make selective ligands; however, the high degree of homology between cannabinoid receptor subtypes introduces challenges in studying either receptor in isolation. Recent advancements in structure biology have resulted in a surge of high-resolution structures, enriching our knowledge and understanding of receptor structure and function. In this review, of recent cannabinoid receptor structures, key features of the inactive and active state CB1 and CB2 are presented. These structures will provide additional insight into the modulation and signaling mechanism of cannabinoid receptors CB1 and CB2 and aid in the development of future therapeutics.

Synthetic cannabinoid receptor agonists: Analytical profiles and development of QMPSB, QMMSB, QMPCB, 2F-QMPSB, QMiPSB, and SGT-233

A diverse assortment of molecules designed to explore the cannabinoid receptor system and considered new psychoactive substances (NPS) have become known as synthetic cannabinoid receptor agonists (SCRAs). One group of SCRAs that has received little attention involves those exhibiting sulfamoyl benzoate, sulfamoyl benzamide, and N-benzoylpiperidine based structures. In this study, quinolin-8-yl 4-methyl-3-(piperidine-1-sulfonyl)benzoate (QMPSB), quinolin-8-yl 4-methyl-3-(morpholine-4-sulfonyl)benzoate (QMMSB), quinolin-8-yl 4-methyl-3-(piperidine-1-carbonyl)benzoate (QMPCB, SGT-11), quinolin-8-yl 3-(4,4-difluoropiperidine-1-sulfonyl)-4-methylbenzoate (2F-QMPSB, QMDFPSB, SGT-13), quinolin-8-yl 4-methyl-3-[(propan-2-yl)sulfamoyl]benzoate (QMiPSB, SGT-46), and 3-(4,4-difluoropiperidine-1-sulfonyl)-4-methyl-N-(2-phenylpropan-2-yl)benzamide (SGT-233) were extensively characterized (including data on impurities). The analytical profiles may be useful to researchers and scientists who deal with the emergence of NPS during forensic and clinical investigations. The detection of QMPSB was first published in 2016 but it is worth noting that Stargate International, a company originally formed to develop harm reduction solutions, were involved in the investigation and development of these six compounds for potential release between 2011 and early 2014. Whilst information on the prevalence of use of these particular compounds at the present time is limited, one of the key outcomes of the research performed by Stargate International reviewed here was to set the stage for the quinolin-8-yl ester head group that ultimately led to hybridization with an N-alkyl-1H-indole core to give SGT-21 and SGT-32, which became later known as PB-22 (QMPSB/JWH-018 hybrid) and BB-22, respectively, thus, opening the door to a range of SCRAs carrying the quinolin-8-yl head group from about 2012 onwards.

High-resolution crystal structure of the human CB1 cannabinoid receptor

The human cannabinoid G-protein-coupled receptors (GPCRs) CB1 and CB2 mediate the functional responses to the endocannabinoids anandamide and 2-arachidonyl glycerol (2-AG) and to the widely consumed plant phytocannabinoid Δ9-tetrahydrocannabinol (THC). The cannabinoid receptors have been the targets of intensive drug discovery efforts, because modulation of these receptors has therapeutic potential to control pain, epilepsy, obesity, and other disorders. Although much progress in understanding the biophysical properties of GPCRs has recently been made, investigations of the molecular mechanisms of the cannabinoids and their receptors have lacked high-resolution structural data. Here we report the use of GPCR engineering and lipidic cubic phase crystallization to determine the structure of the human CB1 receptor bound to the inhibitor taranabant at 2.6-Å resolution. We found that the extracellular surface of CB1, including the highly conserved membrane-proximal N-terminal region, is distinct from those of other lipid-activated GPCRs, forming a critical part of the ligand-binding pocket. Docking studies further demonstrate how this same pocket may accommodate the cannabinoid agonist THC. Our CB1 structure provides an atomic framework for studying cannabinoid receptor function and will aid the design and optimization of therapeutic modulators of the endocannabinoid system.

Computational Prediction and Biochemical Analyses of New Inverse Agonists for the CB1 Receptor

Human cannabinoid type 1 (CB1) G-protein coupled receptor is a potential therapeutic target for obesity. The previously predicted and experimentally validated ensemble of ligand-free conformations of CB1 [Scott, C. E. et al. Protein Sci. 2013 , 22 , 101 - 113 ; Ahn, K. H. et al. Proteins 2013 , 81 , 1304 - 1317] are used here to predict the binding sites for known CB1-selective inverse agonists including rimonabant and its seven known derivatives. This binding pocket, which differs significantly from previously published models, is used to identify 16 novel compounds expected to be CB1 inverse agonists by exploiting potential new interactions. We show experimentally that two of these compounds exhibit inverse agonist properties including inhibition of basal and agonist-induced G-protein coupling activity, as well as an enhanced level of CB1 cell surface localization. This demonstrates the utility of using the predicted binding sites for an ensemble of CB1 receptor structures for designing new CB1 inverse agonists.

Structural Basis of Species-Dependent Differential Affinity of 6-Alkoxy-5-Aryl-3-Pyridinecarboxamide Cannabinoid-1 Receptor Antagonists

6-Alkoxy-5-aryl-3-pyridincarboxamides, including the brain-penetrant compound 14G: [5-(4-chlorophenyl)-6-(cyclopropylmethoxy)-N-[(1R,2R)-2-hydroxy-cyclohexyl]-3-pyridinecarboxamide] and its peripherally restricted analog 14H: [5-(4-chlorophenyl)-N-[(1R,2R)-2-hydroxycyclohexyl]-6-(2-methoxyethoxy)-3-pyridinecarboxamide], have been recently introduced as selective, high-affinity antagonists of the human cannabinoid-1 receptor (hCB1R). Binding analyses revealed two orders of magnitude lower affinity of these compounds for mouse and rat versus human CB1R, whereas the affinity of rimonabant is comparable for all three CB1Rs. Modeling of ligand binding to CB1R and binding assays with native and mutant (Ile105Met) hCB1Rs indicate that the Ile105 to Met mutation in rodent CB1Rs accounts for the species-dependent affinity of 14G: and 14H: . Our work identifies Ile105 as a new pharmacophore component for developing better hCB1R antagonists and invalidates rodent models for assessing the antiobesity efficacy of 14G: and 14H: .

Ligand-specific homology modeling of human cannabinoid (CB1) receptor

Cannabinoid (CB1) receptor is a therapeutic drug target, and its structure and conformational changes after ligand binding are of great interest. To study the protein conformations in ligand bound state and assist in drug discovery, CB1 receptor homology models are needed for computer-based ligand screening. The known CB1 ligands are highly diverse structurally, so CB1 receptor may undergo considerable conformational changes to accept different ligands, which is challenging for molecular docking methods. To account for the flexibility of CB1 receptor, we constructed four CB1 receptor models based on four structurally distinct ligands, HU-210, ACEA, WIN55212-2 and SR141716A, using the newest X-ray crystal structures of human β₂ adrenergic receptor and adenosine A(2A) receptor as templates. The conformations of these four CB1-ligand complexes were optimized by molecular dynamics (MD) simulations. The models revealed interactions between CB1 receptor and known binders suggested by experiments and could successfully discriminate known ligands and non-binders in our docking assays. MD simulations were used to study the most flexible ligand, ACEA, in its free and bound states to investigate structural mobility achieved by the rearrangement of the fatty acid chain. Our models may capture important conformational changes of CB1 receptor to help improve accuracy in future CB1 drug screening.