Molecular insights into the allosteric coupling mechanism between an agonist and two different transducers for μ-opioid receptors

G protein-coupled receptors (GPCRs) as the most important class of pharmacological targets regulate G-protein and beta-arrestin-mediated signaling through allosteric interplay, which are responsible for different biochemical and physiological actions like therapeutic efficacy and side effects. However, the allosteric mechanism underlying preferentially recruiting one transducer versus the other has been poorly understood, limiting drug design. Motivated by this issue, we utilize accelerated molecular dynamics simulation coupled with potential of mean force (PMF), molecular mechanics Poisson Boltzmann surface area (MM/PBSA) and protein structure network (PSN) to study two ternary complex systems of a representative class A GPCR (mu-opioid receptor (mu OR)) bound by an agonist and one specific transducer (G-protein and beta-arrestin). The results show that no significant difference exists in the whole structure of mu OR between two transducer couplings, but displays transducer-dependent changes in the intracellular binding region of mu OR, where the beta-arrestin coupling results in a narrower crevice with TM7 inward movement compared with the G-protein. In addition, both the G-protein and beta-arrestin coupling can increase the binding affinity of the agonist to the receptor. However, the interactions between the agonist and mu OR also exhibit transducer-specific changes, in particular for the interaction with ECL2 that plays an important role in recruiting beta-arrestin. The allosteric network analysis further indicates that Y148(3.33), F152(3.37), F156(3.41), N191(4.49), T160(3.45), Y106(2.42), W293(6.48), F289(6.44), I248(5.54) and Y252(5.58) play important roles in equally activating G-protein and beta-arrestin. In contrast, M161(3.46) and R165(3.50) devote important contributions to preferentially recruit G-protein while D164(3.49) and R179(ICL2) are revealed to be important for selectively activating beta-arrestin. The observations provide useful information for understanding the biased activation mechanism.

Automated summary

This study investigates the allosteric mechanism of G protein-coupled receptors (GPCRs) in recruiting different transducers. The results show that the intracellular binding region of the receptor undergoes transducer-dependent changes, leading to differences in the activation of G-protein and beta-arrestin. The study also reveals specific interactions between the agonist and the receptor that are important for recruiting beta-arrestin. The findings provide valuable insights into biased activation mechanisms.