The 2.1 A Resolution Structure of Cyanopindolol-Bound Beta1- Adrenoceptor Identifies an Intramembrane Na+ Ion that Stabilises the Ligand-Free Receptor.Miller-Gallacher, J.L., Nehme, R., Warne, T., Edwards, P.C., Schertler, G.F.X., Leslie, A.G.W., Tate, C.G.
(2014) Plos One 9: 92727
- PubMed: 24663151
- DOI: 10.1371/journal.pone.0092727
- PubMed Abstract:
The β1-adrenoceptor (β1AR) is a G protein-coupled receptor (GPCR) that is activated by the endogenous agonists adrenaline and noradrenaline. We have determined the structure of an ultra-thermostable β1AR mutant bound to the weak partial agonist cyano ...
The β1-adrenoceptor (β1AR) is a G protein-coupled receptor (GPCR) that is activated by the endogenous agonists adrenaline and noradrenaline. We have determined the structure of an ultra-thermostable β1AR mutant bound to the weak partial agonist cyanopindolol to 2.1 Å resolution. High-quality crystals (100 μm plates) were grown in lipidic cubic phase without the assistance of a T4 lysozyme or BRIL fusion in cytoplasmic loop 3, which is commonly employed for GPCR crystallisation. An intramembrane Na+ ion was identified co-ordinated to Asp872.50, Ser1283.39 and 3 water molecules, which is part of a more extensive network of water molecules in a cavity formed between transmembrane helices 1, 2, 3, 6 and 7. Remarkably, this water network and Na+ ion is highly conserved between β1AR and the adenosine A2A receptor (rmsd of 0.3 Å), despite an overall rmsd of 2.4 Å for all Cα atoms and only 23% amino acid identity in the transmembrane regions. The affinity of agonist binding and nanobody Nb80 binding to β1AR is unaffected by Na+ ions, but the stability of the receptor is decreased by 7.5°C in the absence of Na+. Mutation of amino acid side chains that are involved in the co-ordination of either Na+ or water molecules in the network decreases the stability of β1AR by 5-10°C. The data suggest that the intramembrane Na+ and associated water network stabilise the ligand-free state of β1AR, but still permits the receptor to form the activated state which involves the collapse of the Na+ binding pocket on agonist binding.
Structural Studies Division, MRC Laboratory of Molecular Biology, Cambridge, Cambridgeshire, United Kingdom.