Muscarinic Acetylcholine Receptor Phosphorylation Assays

Muscarinic acetylcholine receptors (M1-M5) are activated by the endogenous agonist acetylcholine. All five M receptors have a widespread tissue distribution and are involved in the control of numerous central and peripheral physiological responses, as well as being a major drug target in human disease. Classically these receptors are sub-divided into two broad groups based on their primary coupling efficiency to G-proteins. M1, M3, and M5 preferentially couple to Gq/11 proteins, whilst M2 and M4 predominantly couple to pertusiss toxin-sensitive Gi/o proteins. Both agonists and antagonists of mAChRs are clinically approved drugs, including pilocarpine for the treatment of elevated intra-ocular pressure and glaucoma, and atropine for the treatment of bradycardia and poisoning by muscarinic agents such as organophosphates. Nevertheless, the orthosteric binding pocket of the muscarinic receptor family is highly conserved, making the development of subtype-specific agonists and antagonists very difficult. Attempts to generate novel muscarinic ligands have more recently centred on the development of allosteric regulators that act at non-conserved sites and therefore offer the prospect of subtype selectivity.