Membrane Mimetic-Dependence of GPCR Energy Landscapes

Protein function strongly depends on temperature, which is related to temperature-dependent changes in the equilibria of protein conformational states. We leveraged variable-temperature ¹⁹ F-NMR spectroscopy to interrogate the temperature dependence of the conformational landscape of the human A _2A adenosine receptor (A _2A AR), a class A GPCR. Temperature-induced changes in the conformational equilibria of A _2A AR in lipid nanodiscs were markedly dependent on the efficacy of bound drugs. While antagonist complexes displayed only modest changes as the temperature rose, both full and partial agonist complexes exhibited substantial increases in the active state population. Importantly, the temperature-dependent response of complexes with both full and partial agonists exhibited a pronounced sensitivity to the specific membrane mimetic employed. In striking contrast to observations within lipid nanodiscs, in detergent micelles the active state population exhibited different behavior for A _2A AR complexes with both full and partial agonists. This underscores the importance of the protein environment in understanding the thermodynamics of GPCR activation.