Membrane mimetic systems modulate GPCR energy landscapes

Arka Prabha Ray¹, Naveen Thakur¹, Beining Jin¹, Nessa P. Afsharian¹, Zhan-Guo Gao², Kenneth A. Jacobson², Matthew T. Eddy¹

1Department of Chemistry, University of Florida, Gainesville, FL, 32611, USA
2Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institute of Health, Bethesda, MD, 20892, USA

G protein-coupled receptors (GPCRs) are sensory membrane proteins that control numerous physiological processes and are targeted by 35% of all FDA approved drugs. Previous NMR studies reported that the function-related conformational dynamics of GPCRs are modulated not only by small molecule ligands but also by lipids, including phospholipids and cholesterol.^1-5 To investigate the impact of the employed membrane mimetic system on GPCR structural plasticity, we utilized ¹⁹F-NMR with detergent micelle and lipid nanodisc preparations of the human A2A adenosine receptor (A_2AAR), a class A GPCR. As receptor function and dynamics are temperature dependent, our study compared A_2AAR conformational dynamics in different membrane mimetics across a range of temperatures, ranging from lower temperatures typically employed in ¹⁹F-NMR experiments (e.g., 273 K) to physiological temperature.

With increasing temperature, lipid nanodisc samples containing A_2AAR complexes with partially activating (partial agonists) and fully activating (agonists) drugs exhibited large increases in the population of a fully active conformation. This effect was particularly pronounced for A_2AAR-complexes with partial agonists, where the population of active A_2AAR was nearly undetectable at lower temperature but became evident at physiological temperature. Our data also show that the temperature-dependent response for complexes with either full or partial agonists exhibited a pronounced sensitivity to the specific membrane mimetic employed. In contrast to observations with lipid nanodiscs, in detergent micelles the active state population exhibited different temperature-dependent behavior for both full and partial agonists complexes. For complexes with partial agonists, the receptor adopted an inactive conformation in detergent micelle preparations even at physiological temperature. Measurements of cellular signaling correlated with the temperature-dependent conformational equilibria of A_2AAR in lipid nanodiscs but not in detergents, underscoring the importance of the membrane environment in studies of GPCR function. The presented data provide clear evidence of the influence of the membrane environment on GPCR conformational dynamics, underscoring the significant influence of the properties of membrane environments on receptor function.

Acknowledgements:

This work was supported by NIH Grant R35GM138291 and NSF DMR1644779.

References:

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