Membrane mimetic-dependence of GPCR energy landscapes.

We leveraged variable-temperature F-NMR spectroscopy to compare the conformational equilibria of the human A adenosine receptor (AAR), a class A G protein-coupled receptor (GPCR), across a range of temperatures ranging from lower temperatures typically employed in F-NMR experiments to physiological temperature. AAR complexes with partial agonists and full agonists showed large increases in the population of a fully active conformation with increasing temperature. NMR data measured at physiological temperature were more in line with functional data. This was pronounced for complexes with partial agonists, where the population of active AAR was nearly undetectable at lower temperature but became evident at physiological temperature. Temperature-dependent behavior of complexes with either full or partial agonists exhibited a pronounced sensitivity to the specific membrane mimetic employed. Cellular signaling experiments correlated with the temperature-dependent conformational equilibria of AAR in lipid nanodiscs but not in some detergents, underscoring the importance of the membrane environment in studies of GPCR function.