The G‐Protein‐Coupled Neuropeptide Y Receptor Type 2 is Highly Dynamic in Lipid Membranes as Revealed by Solid‐State NMR Spectroscopy

In spite of the recent success in crystallizing several G‐protein‐coupled receptors (GPCRs), a comprehensive biophysical characterization of these molecules under physiological conditions also requires the study of the molecular dynamics of these proteins. The molecular mobility of the human neuropeptide Y receptor type 2 reconstituted into dimyristoylphosphatidylcholine (DMPC) membranes was investigated by means of solid‐state NMR spectroscopy. Static 15 N NMR spectra show that the receptor performs axially symmetric motions in the membrane, and several residues undergo large amplitude fluctuations. This was confirmed by quantitative measurements of the motional 1 H, 13 C order parameter of the CH, CH 2 , and CH 3 groups. In directly polarized 13 C NMR experiments, these order parameters showed astonishingly low values of S CH =0.55, S   CH   2=0.33, and S   CH   3=0.17, which corresponds to segmental amplitudes of approximately 50° in the backbone and approximately 50–60° in the side chain. At physiological temperature, 2 H NMR spectra of the deuterated receptor showed a narrow component that is indicative of molecular order parameters of S ≤0.3 superimposed with a very broad spectrum that could stem from the transmembrane α‐helices. These results suggest that the crystal structures of GPCRs only represent a static snapshot of these highly mobile molecules, which undergo significant structural fluctuations with relatively large amplitudes in a liquid‐crystalline membrane at physiological temperature.