Investigation of Muscarinic Acetylcholine Receptor M₃ Activation in Atomistic Detail: A Chemist's Viewpoint

We analyzed the precise ligand:receptor interactions required for activation of the muscarinic acetylcholine receptor M₃, a prototypical G protein-coupled receptor and potential diabetes target. Starting from literature-known compounds and docking solutions, ligands were tailored for the modulation of this receptor's activation. Several aspects of the structure-activity relationship of agonists were investigated in atomistic detail, in order to delineate how the receptor can be activated via the orthosteric site. Such exquisitely precise knowledge is instrumental for designing potent and effiacious ligands. We put this strategy into practice and acquired or synthesized and measured a diverse set of 55 ligands ranging from small fragment-like amines coordinating D^3.32 to bigger molecules extending towards helices 5 and 6 with diphenyl moieties. In the course of these investigations, we showed that the polarizability of the amine nitrogen and the rigidity and size of the moieties in the space delimited by helices 5 and 6 are the two key elements distinguishing potent and efficacious ligands from those that are not. The resulting data set will be highly useful in drug design and molecular machine learning alike.