Direct effect of membrane environment on the activation of mGluR2 revealed by single-molecule FRET.

The microenvironment of membrane receptors controls their mobility, structure, interactions, and dynamics, but a systematic understanding of how it modulates receptor function is often lacking. Using single-molecule Förster resonance energy transfer (smFRET), we characterized how detergents and cholesterol modulate the conformational dynamics of metabotropic glutamate receptor 2 (mGluR2), a class C G protein-coupled receptor (GPCR). We found that, within the resolution of our measurements, all tested detergents stabilize the same overall active and inactive structure of different domains of mGluR2. However, the degree of stabilization and the equilibrium between active and inactive conformations depended on the detergent. Detergents with a single hydrophobic tail increased the active state occupancy compared to those with long, branched tails. Adding cholesterol to micelles with branched hydrophobic tails shifted the equilibrium toward the inactive state. Mutagenesis identified residues potentially involved in cholesterol interaction with mGluR2. Targeting the cholesterol-binding site with synthetic molecules could be a viable therapeutic approach.