GDP Release from the Open Conformation of Gα Requires Allosteric Signaling from the Agonist-Bound Human β₂ Adrenergic Receptor

Abstract

G-protein-coupled receptors (GPCRs) transmit signals into the cell in response to ligand binding at its extracellular domain, which is characterized by the coupling of agonist-induced receptor conformational change to guanine nucleotide (GDP) exchange with guanosine triphosphate on a heterotrimeric (αβγ) guanine nucleotide-binding protein (G-protein), leading to the activation of the G-protein. The signal transduction mechanisms have been widely researched in vivo and in silico. However, coordinated communication from stimulating ligands to the bound GDP still remains elusive. In the present study, we used microsecond (μS) molecular dynamic (MD) simulations to directly probe the communication from the β 2 adrenergic receptor (β 2 AR) with an agonist or an antagonist or no ligand to GDP bound to the open conformation of the Gα protein. Molecular mechanism-general Born surface area calculation results indicated either the agonist or the antagonist destabilized the binding between the receptor and the G-protein but the agonist caused a higher level of destabilization than the antagonist. This is consistent with the role of agonist in the activation of the G-protein. Interestingly, while GDP remained bound with the Gα-protein for the two inactive systems (antagonist-bound and apo form), GDP dissociated from the open conformation of the Gα protein for the agonist activated system. Data obtained from MD simulations indicated that the receptor and the Gα subunit play a big role in coordinated communication and nucleotide exchange. Based on residue interaction network analysis, we observed that engagement of agonist-bound β 2 AR with an α5 helix of G α is essential for the GDP release and the residues in the phosphate-binding loop, α1 helix, and α5 helix play very important roles in the GDP release. The insights on GPCR−G-protein communication will facilitate the rational design of agonists and antagonists that target both active and inactive GPCR binding pockets, leading to more precise drugs.

The nuclear receptor LRH-1 discriminates between ligands using distinct allosteric signaling circuits

“…Activating ligands induce coordinated, productive motions with residues in helix 7 and AFB, attenuating signaling to the AF-H. Tif2 communicates via coordinated motions or destabilizing fluctuations depending on ligand status. Both types of allosteric communication have been reported in other systems (30)(31)(32)(33)(34)(35).…”

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

“…29,30 However, previous MD works 29,30 on GPCRs have mainly studied binary complexes composed of the receptor and the ligand, not involving the downstream transducers due to paucity of the crystal structures of the ternary complex. With several crystal structures of the ternary complexes recently resolved, some MD research [31][32][33][34][35] began to study them, yet most of this focused on the ternary complex only coupled with one transducer (mainly for G-protein and less for b-arrestin). These studies provide valuable information for understanding one specific biased activation, but lack important information regarding the differences between the G-protein and b-arrestin activation.…”

Biased Signaling in Mutated Variants of β2-Adrenergic Receptor: Insights from Molecular Dynamics Simulations

“…In particular, simulation results show the role of critical residues and structural motifs responsible for transmitting allosteric signals from the agonist to the transducer-binding regions; TM3 and TM7 residues act as allosteric communication hubs in GRK/β-arrestin selective signaling, whereas TM5 residues favor G protein signaling. The residues and allosteric functional regions in β 2 AR, identified in the present study, can be targeted to design novel biased drugs, as information about functional hotspots in β-adrenergic receptors has been demonstrated to assist in delineating the mechanism of agonist-induced activation and biased signaling. ,,,,− …”