Insight into partial agonism by observing multiple equilibria for ligand-bound and Gs-mimetic nanobody-bound β1-adrenergic receptor

• Published in: Nature communications 2017-11, Vol.8 (1), p.1-12, Article 1795
• Main Authors: Solt, Andras S., Bostock, Mark J., Shrestha, Binesh, Kumar, Prashant, Warne, Tony, Tate, Christopher G., Nietlispach, Daniel
• Format: Article
• Language: English
• Subjects: 631/45/612/194; 631/535/878/1263; Adrenergic receptors; Arrestin; Coordination compounds; G protein-coupled receptors; Humanities and Social Sciences; Intracellular signalling; Ligands; Methionine; multidisciplinary; Nanobodies; NMR; Nuclear magnetic resonance; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-017-02008-y

A complex conformational energy landscape determines G-protein-coupled receptor (GPCR) signalling via intracellular binding partners (IBPs), e.g., G s and β-arrestin. Using 13 C methyl methionine NMR for the β 1 -adrenergic receptor, we identify ligand efficacy-dependent equilibria between an inactive and pre-active state and, in complex with G s -mimetic nanobody, between more and less active ternary complexes. Formation of a basal activity complex through ligand-free nanobody–receptor interaction reveals structural differences on the cytoplasmic receptor side compared to the full agonist-bound nanobody-coupled form, suggesting that ligand-induced variations in G-protein interaction underpin partial agonism. Significant differences in receptor dynamics are observed ranging from rigid nanobody-coupled states to extensive μs-to-ms timescale dynamics when bound to a full agonist. We suggest that the mobility of the full agonist-bound form primes the GPCR to couple to IBPs. On formation of the ternary complex, ligand efficacy determines the quality of the interaction between the rigidified receptor and an IBP and consequently the signalling level. β 1 -adrenergic receptors are expressed in cardiac tissue and stimulated by the sympathetic nervous system. Here, the authors use NMR spectroscopy to unravel the conformational diversity upon β 1 -adrenergic receptor activation and provide structural insights into partial agonism and basal activity.