Interplay between Two Allosteric Sites and Their Influence on Agonist Binding in Human μ Opioid Receptor

Allostery is a widespread mechanism that allows for precise protein tuning. Its underlying mechanisms are elusive, particularly when there are multiple allosteric sites at the protein. This concerns also G-protein-coupled receptors (GPCRs), which are targets for a vast part of currently used drugs. To address this issue, we performed molecular dynamics simulations of a GPCR–human μ opioid receptor (MOR) in a native-like environment, with full agonist (R)-methadone, Na+ ions, and a positive modulator BMS986122 in various configurations. We found that MOR's seventh transmembrane helix (TM VII) is central for allosteric signal transmission, and modulators affect its bending and rotation. The PAM stabilizes favorable agonist interactions, while Na+ tends to disrupt agonist binding. We identified two residues involved in allosteric signal transmission: Trp 7.35 at the top and Tyr 7.53 at the bottom of TM VII.