Towards the Crystal Structure Determination of Muscarinic Acetylcholine Receptors

Abstract

G protein-coupled receptors (GPCRs) constitute the largest family of receptors encoded by the human genome. Activation and inhibition of GPCRs under the physiological and pathophysiological conditions is largely mediated by chemical ligands (agonists and antagonists) that bind to the orthosteric binding pocket. Orthosteric ligands are, however, often nonspecific, binding to more than one GPCR subtype. In contrast to orthosteric agonists and antagonists, allosteric ligands do not directly compete with hormones and neurotransmitters for binding to the orthosteric binding pocket. Furthermore, allosteric ligands typically occupy structurally diverse regions of receptors and therefore are more selective for specific GPCRs, regulating receptor function in the more subtle ways by either enhancing or diminishing responses to natural ligands such as hormones or neurotransmitters. Recent X-ray crystallographic studies have provided detailed structural information regarding the nature of the orthosteric muscarinic binding site and an outer receptor cavity that can bind allosteric drugs. These new findings may guide the development of selective muscarinic receptor. The procedures involved in the production, purification, and crystallization of GPCRs are introduced here and facilitate a greater understanding of the structural basis of GPCR function.