Understanding the role of the CB1 toggle switch in interaction networks using molecular dynamics simulation

Abstract

The cannabinoid receptor 1 (CB1) is a class A G-protein coupled receptor (GPCR) that can exert various effects on the human body through the endocannabinoid system. Understanding CB1 activation has many benefits for the medical use of cannabinoids. A previous study reported that CB1 has two notable residues referred to as the toggle switch, F3.36 and W6.48, which are important for its activation mechanism. We performed a molecular dynamics simulation with a mutation in the toggle switch to examine its role in active and inactive states. We also examined structural changes, the residue–residue interaction network, and the interaction network among helices and loops of wildtype and mutant CB1 for both activation states. As a result, we found that the energetic changes in the hydrogen-bond network of the Na+ pocket, extracellular N-terminus–TM2–ECL1–TM3 interface including D2.63–K3.28 salt-bridge, and extracellular ECL2–TM5–ECL3–TM6 interface directly linked to the toggle switch contribute to the stability of CB1 by the broken aromatic interaction of the toggle switch. It makes the conformation of inactive CB1 receptor to be unstable. Our study explained the role of the toggle switch regarding the energetic interactions related to the Na+ pocket and extracellular loop interfaces, which could contribute to a better understanding of the activation mechanism of CB1.

Synthesis and Functional Evaluation of Synthetic Cannabinoid Receptor Agonists Related to ADB-HEXINACA

“…The indole, indazole, and 7-azaindole core of each ligand was stabilized by edge-to-face π–π interactions with Phe200 and Phe268. The Phe200 interaction is particularly important in CB 1 activation, as it makes up one-half of the CB 1 “toggle switch” along with Trp356 . As Phe200 rotates to interact with the ligand, it allows Trp356 to also rotate, which results in an outward translation of the cytoplasmic end of TM6, allowing the receptor to adopt an active conformation.…”

“…The Phe200 interaction is particularly important in CB 1 activation, as it makes up one-half of the CB 1 "toggle switch" along with Trp356. 58 As Phe200 rotates to interact with the ligand, it allows Trp356 to also rotate, which results in an outward translation of the cytoplasmic end of TM6, allowing the receptor to adopt an active conformation. The hexyl and 5hexenyl tail groups of the docked compounds occupy the hydrophobic pocket of the orthosteric side between TM3 and TM5, stabilized by lipophilic interactions with the residues Ile271, Tyr275, Leu276, Phe268, and Trp279.…”

Electrostatics in Computational Biophysics and Its Implications for Disease Effects

“…It was shown that if SB1 is broken, the mechanical stability of ubiquitin increases slightly, but when SB2 is broken, the stability reduces significantly [ 65 ]. Stability and activity are typically related, and thus a study on a particular G-protein coupled receptor (GPCR), the cannabinoid receptor 1 (CB1), indicated that the switching mechanism involves a salt bridge, the D263–K328 salt-bridge, that contributes to the stability of CB1 [ 66 ]. Salt-bridge involvement in the activation mechanism of calcium-dependent protein kinase-1 further elucidates the role of short-range interactions in molecular biology.…”

“…Recent work focused on calcium-dependent protein kinase-1 of Plasmodium falciparum (PfCDPK1) and explored the possibility of allosteric inhibition of this kinase. It showed how the truncation of CAD in PfCDPK1 disrupts a conserved salt-bridge required for stabilizing the kinase domain in an active state, and the kinase domain adopts an inactive conformation [ 66 ]. Similarly, the role of a salt bridge, His59–Asp103, in human granzyme B (hGzmB) was studied.…”

Differential Behavior of Conformational Dynamics in Active and Inactive States of Cannabinoid Receptor 1

“…4,5,[37][38][39] Recent studies have shown that some GPCRs exhibit increased flexibility in the inactive state compared to the active state in apo form, contrary to the traditional understanding. 4,[39][40][41] For example, microsecond-timescale MD simulations of the β2-adrenergic receptor revealed greater conformational heterogeneity in the inactive state, while displaying active-like conformational elements. 42 CB1 is a Class A GPCR that binds endogenous cannabinoids as well as exogenous ligands such as tetrahydrocannabinol (THC), 43 the primary psychoactive constituent of cannabis.…”