Conserved Binding Mode of Human β2 Adrenergic Receptor Inverse Agonists and Antagonist Revealed by X-ray Crystallography

Abstract

G protein-coupled receptors (GPCRs) represent a large fraction of current pharmaceutical targets, and of the GPCRs, the β₂ adrenergic receptor (β₂AR) is one of the most extensively studied. Previously, the X-ray crystal structure of β₂AR has been determined in complex with two partial inverse agonists, but the global impact of additional ligands on the structure or local impacts on the binding site are not well-understood. To assess the extent of such ligand-induced conformational differences, we determined the crystal structures of a previously described engineered β₂AR construct in complex with two inverse agonists: ICI 118,551 (2.8 Å), a recently described compound (2.8 Å) (Kolb et al, 2009), and the antagonist alprenolol (3.1 Å). The structures show the same overall fold observed for the previous β₂AR structures and demonstrate that the ligand binding site can accommodate compounds of different chemical and pharmacological properties with only minor local structural rearrangements. All three compounds contain a hydroxy-amine motif that establishes a conserved hydrogen bond network with the receptor and chemically diverse aromatic moieties that form distinct interactions with β₂AR. Furthermore, receptor ligand cross-docking experiments revealed that a single β₂AR complex can be suitable for docking of a range of antagonists and inverse agonists but also indicate that additional ligand−receptor structures may be useful to further improve performance for in-silico docking or lead-optimization in drug design.