A high-resolution description of β 1 -adrenergic receptor functional dynamics and allosteric coupling from backbone NMR

Signal transmission and regulation of G-protein-coupled receptors (GPCRs) by extra- and intracellular ligands occurs via modulation of complex conformational equilibria, but their exact kinetic details and underlying atomic mechanisms are unknown. Here we quantified these dynamic equilibria in the β -adrenergic receptor in its apo form and seven ligand complexes using H/ N NMR spectroscopy. We observe three major exchanging conformations: an inactive conformation (C ), a preactive conformation (C ) and an active conformation (C ), which becomes fully populated in a ternary complex with a G protein mimicking nanobody. The C ↔ C exchange occurs on the microsecond scale, the C ↔ C exchange is slower than ~5 ms and only occurs in the presence of two highly conserved tyrosines (Y , Y ), which stabilize the active conformation of TM6. The C →C chemical shift changes indicate a pivoting motion of the entire TM6 that couples the effector site to the orthosteric ligand pocket.