Visualizing the M2 muscarinic acetylcholine receptor activation regulated by aromatic ring dynamics

A detailed molecular understanding of the G-protein coupled receptor (GPCR) activation mechanism is crucial for rational drug design. Despite the growing number of GPCR structures being resolved in the inactive and activated states, the detailed molecular mechanism of how receptors transits from the inactive towards the active one upon agonist binding remains to be further understood. Herein, we performed comprehensive atomic-level simulations of the M2 muscarinic receptor (M2R) to determine how ligand binding modulates the receptor conformational dynamics. The results reveal that aromatic residue dynamics are closely associated with receptor activation. Binding of antagonists or agonists differentially alters the interacting patterns of critical aromatic residues, stabilizing them into distinct conformations. In addition, we found that the change of interaction and dynamics of the W400 ^6.48 -F396 ^6.44 pair at the transmembrane core plays an essential role in the structural transition of M2R from the inactive state into an active-like state induced by binding of the supra-physiological agonist iperoxo. Moreover, we found that the sidechain dynamics of Y206 ^5.58 is important in modulating the conformation of the intracellular cavity. Our work highlights the role of protein conformational dynamics in M2R activation, and provides new insights for future drug designs.