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(1)-adrenergic receptor in its apo form and seven ligand complexes using (1)H/(15)N NMR spectroscopy. We observe three major exchanging conformations: an inactive conformation (C(i)), a preactive conformation (C(p)) and an active conformation (C(a)), which becomes fully populated in a ternary complex with a G protein mimicking nanobody. The C(i) ↔ C(p) exchange occurs on the microsecond scale, the C(p) ↔ C(a) exchange is slower than ~5 ms and only occurs in the presence of two highly conserved tyrosines (Y(5.58), Y(7.53)), which stabilize the active conformation of TM6. The C(p)→C(a) chemical shift changes indicate a pivoting motion of the entire TM6 that couples the effector site to the orthosteric ligand pocket.