The Implication of the First Agonist Bound Activated GPCR X-ray Structure on GPCR in Silico Modeling

The very recently published first X-ray structure of the β2 adrenergic receptor in its active state hosting a small molecule (PDB ID: 3P0G) reveals a lot of information about the G-protein-coupled receptor (GPCR) activation process from a structural point of view. When compared to the inactive state crystal structure of β2, large differences are seen in the GPCR helical structure at the cytoplasmatic side, whereas very subtle changes occur at the ligand binding site. The observation that there are hardly any differences in the binding site of agonists and inverse agonists implies that in silico predictions of the efficacy of ligands will be very hard. This is illustrated by the example of an already published binding mode of a β2 agonist, which has been modeled into the inactive state X-ray structure of the β2 receptor. When comparing the modeled structure to the new activated X-ray structure, quantitative agreement of the binding mode is found, implying that the subtle changes between agonist binding to the activated state and inverse agonist binding to the inactive state can currently not be captured by standard in silico modeling methods.