G protein-coupled receptors (GPCRs) are critical eukaryotic signal transduction gatekeepers and represent the largest protein family in the human proteome, with more than 800 members. In recent years, X-ray crystallography has yielded many G protein-coupled receptor structures but the mechanism of allosteric signaling remains unknown. X-ray crystallography of GPCRs requires multiple forms of receptor stabilization that, subsequently, limit conformational dynamics.
Directed evolution of GPCRs enables milligram quantities of functional, isotopically-labeled protein to be produced from prokaryotic expression systems. This technology opens the field for NMR studies of GPCRs with various ligands and in complex with G proteins and arrestins. Focusing on the neurotensin receptor, We use NMR spectroscopy to probe the structure and conformational dynamics of GPCR activation in solution.