Difference and Influence of Inactive and Active States of Cannabinoid Receptor Subtype CB2: From Conformation to Drug Discovery

Abstract

Cannabinoid receptor 2 (CB2), a G protein-coupled receptor (GPCR), is a promising target for the treatment of neuropathic pain, osteoporosis, immune system, cancer, and drug abuse. The lack of an experimental three-dimensional CB2 structure has hindered not only the development of studies of conformational differences between the inactive and active CB2 but also the rational discovery of novel functional compounds targeting CB2. In this work, we constructed models of both inactive and active CB2 by homology modeling. Then we conducted two comparative 100 ns molecular dynamics (MD) simulations on the two systems—the active CB2 bound with both the agonist and G protein and the inactive CB2 bound with inverse agonist—to analyze the conformational difference of CB2 proteins and the key residues involved in molecular recognition. Our results showed that the inactive CB2 and the inverse agonist remained stable during the MD simulation. However, during the MD simulations, we observed dynamical details about the breakdown of the “ionic lock” between R1313.50 and D2406.30 as well as the outward/inward movements of transmembrane domains of the active CB2 that bind with G proteins and agonist (TM5, TM6, and TM7). All of these results are congruent with the experimental data and recent reports. Moreover, our results indicate that W2586.48 in TM6 and residues in TM4 (V1644.56–L1694.61) contribute greatly to the binding of the agonist on the basis of the binding energy decomposition, while residues S180–F183 in extracellular loop 2 (ECL2) may be of importance in recognition of the inverse agonist. Furthermore, pharmacophore modeling and virtual screening were carried out for the inactive and active CB2 models in parallel. Among all 10 hits, two compounds exhibited novel scaffolds and can be used as novel chemical probes for future studies of CB2. Importantly, our studies show that the hits obtained from the inactive CB2 model mainly act as inverse agonist(s) or neutral antagonist(s) at low concentration. Moreover, the hit from the active CB2 model also behaves as a neutral antagonist at low concentration. Our studies provide new insight leading to a better understanding of the structural and conformational differences between two states of CB2 and illuminate the effects of structure on virtual screening and drug design.

Selective Cannabinoid 2 Receptor Stimulation Reduces Tubular Epithelial Cell Damage after Renal Ischemia-Reperfusion Injury

“…No experimental CB2 structures are currently available from methods such as X-ray or nuclear magnetic resonance spectroscopy. However, there is a long history of use of protein models for study of the CB2 receptor and its interactions with ligands (Cichero et al, 2011;Brents et al, 2012;Kusakabe et al, 2013;Feng et al, 2014;Dore et al, 2016;Hu et al, 2016). As is typical for GPCRs, full agonists and partial agonists bind to and/or stabilize the active state of the CB2 receptor.…”

Structural insight into the serotonin (5-HT) receptor family by molecular docking, molecular dynamics simulation and systems pharmacology analysis

“…Additionally, the energies of each residue were decomposed into the backbone and side-chain atoms. The energy decomposition can be analyzed to determine the contributions of the key residues to the binding [50].…”

Understanding the common themes and diverse roles of the second extracellular loop (ECL2) of the GPCR super-family

“…Residues in the C-terminus of the cannabinoid receptor 1 (CB1) ECL2 were important for agonist binding but not inverse agonist binding (Ahn et al, 2009). Modelling also implicated ECL2 in inverse agonist binding in the cannabinoid receptor subtype CB2 (Hu et al, 2016). Analysis of the crystal structures of β1AR and serotonin receptor crystal structures found ECL2 to be involved in the binding to different ligands to the same receptor (β1AR) or an altered docking of the same ligand to different receptors (5-HT1B and 5-HT2B) (Shukla et al, 2014).…”