RT Journal Article SR Electronic T1 A New Molecular Mechanism To Engineer Protean Agonism at a G Protein–Coupled Receptor JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 348 OP 356 DO 10.1124/mol.116.107276 VO 91 IS 4 A1 De Min, Anna A1 Matera, Carlo A1 Bock, Andreas A1 Holze, Janine A1 Kloeckner, Jessica A1 Muth, Mathias A1 Traenkle, Christian A1 De Amici, Marco A1 Kenakin, Terry A1 Holzgrabe, Ulrike A1 Dallanoce, Clelia A1 Kostenis, Evi A1 Mohr, Klaus A1 Schrage, Ramona YR 2017 UL http://molpharm.aspetjournals.org/content/91/4/348.abstract AB Protean agonists are of great pharmacological interest as their behavior may change in magnitude and direction depending on the constitutive activity of a receptor. Yet, this intriguing phenomenon has been poorly described and understood, due to the lack of stable experimental systems and design strategies. In this study, we overcome both limitations: First, we demonstrate that modulation of the ionic strength in a defined experimental set-up allows for analysis of G protein–coupled receptor activation in the absence and presence of a specific amount of spontaneous receptor activity using the muscarinic M2 acetylcholine receptor as a model. Second, we employ this assay system to show that a dualsteric design principle, that is, molecular probes, carrying two pharmacophores to simultaneously adopt orthosteric and allosteric topography within a G protein–coupled receptor, may represent a novel approach to achieve protean agonism. We pinpoint three molecular requirements within dualsteric compounds that elicit protean agonism at the muscarinic M2 acetylcholine receptor. Using radioligand-binding and functional assays, we posit that dynamic ligand binding may be the mechanism underlying protean agonism of dualsteric ligands. Our findings provide both new mechanistic insights into the still enigmatic phenomenon of protean agonism and a rationale for the design of such compounds for a G protein–coupled receptor.