Vibrational spectroscopy analysis of ligand efficacy in human M2 muscarinic acetylcholine receptor (M2R)
Kota Katayama, Kohei Suzuki, Ryoji Suno, Ryoji Kise, Hirokazu Tsujimoto, So Iwata, Asuka Inoue, Takuya Kobayashi, Hideki Kandori
Abstract
Abstract The intrinsic efficacy of ligand binding to G protein-coupled receptors (GPCRs) reflects the ability of the ligand to differentially activate its receptor to cause a physiological effect. Here we use attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy to examine the ligand-dependent conformational changes in the human M 2 muscarinic acetylcholine receptor (M 2 R). We show that different ligands affect conformational alteration appearing at the C=O stretch of amide-I band in M 2 R. Notably, ATR-FTIR signals strongly correlated with G-protein activation levels in cells. Together, we propose that amide-I band serves as an infrared probe to distinguish the ligand efficacy in M 2 R and paves the path to rationally design ligands with varied efficacy towards the target GPCR.