Ligand-Specific Interactions Modulate Kinetic, Energetic, and Mechanical Properties of the Human β2 Adrenergic Receptor

G protein-coupled receptors (GPCRs) are a class of versatile proteins that transduce signals across membranes. Extracellular stimuli induce inter- and intramolecular interactions that change the functional state of GPCRs and activate intracellular messenger molecules. How these interactions are established and how they modulate the functional state of GPCRs remain to be understood. We used dynamic single-molecule force spectroscopy to investigate how ligand binding modulates the energy landscape of the human beta(2) adrenergic receptor (beta(2)AR). Five different ligands representing either agonists, inverse agonists or neutral antagonists established a complex network of interactions that tuned the kinetic, energetic, and mechanical properties of functionally important structural regions of beta(2)AR. These interactions were specific to the efficacy profile of the ligands investigated and suggest that the functional modulation of GPCRs follows structurally well-defined interaction patterns.