Mechanistic insights into allosteric regulation of the A2A adenosine G protein-coupled receptor by physiological cations

Abstract

Cations play key roles in regulating G-protein-coupled receptors (GPCRs), although their mechanisms are poorly understood. Here, 19F NMR is used to delineate the effects of cations on functional states of the adenosine A2A GPCR. While Na+ reinforces an inactive ensemble and a partial-agonist stabilized state, Ca2+ and Mg2+ shift the equilibrium toward active states. Positive allosteric effects of divalent cations are more pronounced with agonist and a G-protein-derived peptide. In cell membranes, divalent cations enhance both the affinity and fraction of the high affinity agonist-bound state. Molecular dynamics simulations suggest high concentrations of divalent cations bridge specific extracellular acidic residues, bringing TM5 and TM6 together at the extracellular surface and allosterically driving open the G-protein-binding cleft as shown by rigidity-transmission allostery theory. An understanding of cation allostery should enable the design of allosteric agents and enhance our understanding of GPCR regulation in the cellular milieu.

Mechanism of µ-Opioid Receptor-Magnesium Interaction and Positive Allosteric Modulation

“…Based on the RDF shown in Fig. S1, and in agreement with published work (18), the closest minimum distances were min = 2.9 Å and min = 4.8 Å for Na + and Mg 2+ cations, respectively, suggesting that unlike Na + , Mg 2+ binds to the protein through water molecules only. This is reasonable given that the Mg 2+ hydration free-energy is known to be five times larger than the one of the Na + cations (36).…”

“…While the monovalent Na + cation can decrease agonist affinity at the MOP receptor (8), most likely though stabilization of the inactive conformational state of the receptor (e.g., see (9,10)), the divalent Mg 2+ cation has the opposite effect (e.g., see (11)), suggesting it stabilizes an active-like conformation of the receptor. Notably, similar conclusions were drawn for other GPCRs based on inferences from biochemical and pharmacological studies (12)(13)(14)(15)(16)(17)(18).…”

“…While various high-resolution X-ray crystal structures of inactive forms of GPCRs have revealed the atomic details of Na + binding (19)(20)(21)(22), and several MD simulation studies have supported the stabilization of inactive conformations of the receptor by this monovalent cation (e.g., see (9,10,23,24)), limited information exists to date about the preferred binding site(s) of Mg 2+ and the molecular mechanism underlying the potential positive allosteric effect of this divalent cation. A recent interdisciplinary study combining the results of 19 F-NMR and MD simulations on another prototypic GPCR, the adenosine A2A receptor (18), provided further support to the negative allosteric modulation of receptors by Na + and their positive allosteric modulation by Ca 2+ and Mg 2+ . Not only did this work allow to quantify the effects of these cations on the conformational ensemble of the adenosine A2A receptor, but it also suggested important molecular determinants involved in the allosteric activation of this receptor in the presence of physiological cations.…”

Allosteric modulation of G protein‐coupled receptors by amiloride and its derivatives. Perspectives for drug discovery?

“…In a later study by the same team, the effects of NaCl were analyzed, leading to the conclusion that sodium ions reinforce an inactive ensemble of states (S 1‐2 ), as well as the partial‐agonist, stabilized state (S 3 ). HMA competed with the sodium ions, reflected in its effects on both line broadening and chemical shift perturbations in the 23 Na NMR binding isotherm …”

Allosteric regulation of Glutamate dehydrogenase deamination activity

“…Moreover, allosteric transmission persists of a wide range of energy cut-off indicates robust allosteric communication that means small changes in hydrogen bonding network will not significantly affect the allosteric transmission. (Kim et al, 2017;Ye et al, 2018).…”