Molecular basis for high affinity agonist binding in GPCRs
By Andrew Doré | May 9, 2019
G protein-coupled receptors (GPCRs) in the G protein-coupled active state have higher affinity for agonists compared to when they are in the inactive state, but the molecular basis for this is unclear. We have determined four active-state structures of the β1-adrenoceptor (β1AR) bound to conformation-specific nanobodies in the presence of agonists of varying efficacy. Comparison with inactive-state structures of β1AR bound to the identical ligands showed a 24-42% reduction in the volume of the orthosteric binding site. Potential hydrogen bonds were also shorter, and there was up to a 30% increase in the number of atomic contacts between the receptor and ligand. This explains the increase in agonist affinity of GPCRs in the active state for a wide range of structurally distinct agonists.