Conformational plasticity of ligand-bound and ternary GPCR complexes studied by 19 F NMR of the β 1 -adrenergic receptor

• Published in: Nature communications 2020-02, Vol.11 (1), p.669
• Main Authors: Frei, J Niclas, Broadhurst, Richard W, Bostock, Mark J, Solt, Andras, Jones, Andrew J Y, Gabriel, Florian, Tandale, Aditi, Shrestha, Binesh, Nietlispach, Daniel
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Cell Membrane - metabolism; Fluorine-19 Magnetic Resonance Imaging; Humans; Ligands; Membrane Proteins - chemistry; Models, Molecular; Protein Conformation; Receptors, Adrenergic, beta-1 - chemistry; Receptors, Adrenergic, beta-1 - isolation & purification; Receptors, Adrenergic, beta-1 - metabolism; Receptors, G-Protein-Coupled - chemistry; Receptors, G-Protein-Coupled - metabolism
• ISSN: 2041-1723

G-protein-coupled receptors (GPCRs) are allosteric signaling proteins that transmit an extracellular stimulus across the cell membrane. Using F NMR and site-specific labelling, we investigate the response of the cytoplasmic region of transmembrane helices 6 and 7 of the β -adrenergic receptor to agonist stimulation and coupling to a G -protein-mimetic nanobody. Agonist binding shows the receptor in equilibrium between two inactive states and a pre-active form, increasingly populated with higher ligand efficacy. Nanobody coupling leads to a fully active ternary receptor complex present in amounts correlating directly with agonist efficacy, consistent with partial agonism. While for different agonists the helix 6 environment in the active-state ternary complexes resides in a well-defined conformation, showing little conformational mobility, the environment of the highly conserved NPxxY motif on helix 7 remains dynamic adopting diverse, agonist-specific conformations, implying a further role of this region in receptor function. An inactive nanobody-coupled ternary receptor form is also observed.