GPCRs through the keyhole: the role of protein flexibility in ligand binding to ?-adrenoceptors

Emtage, Abigail L.; Mistry, Shailesh N.; Fischer, Peter M.; Kellam, Barrie; Laughton, Charles A.

Abstract

© 2016 Informa UK Limited, trading as Taylor & Francis Group. G protein-coupled receptors (GPCRs) are proteins of pharmaceutical importance, with over 30% of all drugs in clinical use targeting them. Increasing numbers of X-ray crystal (XRC) structures of GPCRs offer a wealth of data relating to ligand binding. For the β-adrenoceptors (β-ARs), XRC structures are available for human β2- and turkey β1-subtypes, in complexes with a range of ligands. While these structures provide insight into the origins of ligand structure-activity relationships (SARs), questions remain. The ligands in all published complexed XRC structures lack extensive substitution, with no obvious way the ligand-binding site can accommodate β1-AR-selective antagonists with extended side-chains para- to the common aryloxypropanolamine pharmacophore. Using standard computational docking tools with such ligands generally returns poses that fail to explain known SARs. Application of our Active Site Pressurisation modelling method to β-AR XRC structures and homology models, however, reveals a dynamic area in the ligand-binding pocket that, through minor changes in amino acid side chain orientations, opens a fissure between transmembrane helices H4 and H5, exposing intra-membrane space. This fissure, which we term the “keyhole”, is ideally located to accommodate extended moieties present in many high-affinity β1-AR-selective ligands, allowing the rest of the ligand structure to adopt a canonical pose in the orthosteric binding site. We propose the keyhole may be a feature of both β1- and β2-ARs, but that subtle structural differences exist between the two, contributing to subtype-selectivity. This has consequences for the rational design of future generations of subtype-selective ligands for these therapeutically important targets.

Citation

Emtage, A. L., Mistry, S. N., Fischer, P. M., Kellam, B., & Laughton, C. A. (2017). GPCRs through the keyhole: the role of protein flexibility in ligand binding to ?-adrenoceptors. Journal of Biomolecular Structure and Dynamics, 35(12), 2604-2619. https://doi.org/10.1080/07391102.2016.1226197

• Journal Article Type: Article
• Acceptance Date: Aug 15, 2016
• Online Publication Date: Aug 17, 2016
• Publication Date: Sep 10, 2017
• Deposit Date: Nov 10, 2016
• Publicly Available Date: Nov 10, 2016
• Journal: Journal of Biomolecular Structure and Dynamics
• Print ISSN: 0739-1102
• Electronic ISSN: 1538-0254
• Publisher: Taylor & Francis Open
• Peer Reviewed: Peer Reviewed
• Volume: 35
• Issue: 12
• Pages: 2604-2619
• DOI: https://doi.org/10.1080/07391102.2016.1226197
• Keywords: GPCRs, beta adrenergic receptor, modelling, docking, active site pressurisation, molecular dynamics, protein flexibility
• Public URL: https://nottingham-repository.worktribe.com/output/805343
• Publisher URL: http://www.tandfonline.com/doi/full/10.1080/07391102.2016.1226197
• Additional Information: This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of Biomolecular Structure and Dynamics on 17/08/2016, available online: http://www.tandfonline.com/10.1080/07391102.2016.1226197