A high-resolution description of β1-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 beta(1)-adrenergic receptor in its apo form and seven ligand complexes using H-1/N-15 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 similar to 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.