Structure of the human M2 muscarinic acetylcholine receptor bound to an antagonist

Abstract

The parasympathetic limb of the autonomic nervous system regulates the activity of multiple organ systems. Muscarinic receptors are G protein coupled receptors (GPCRs) that mediate the response to acetylcholine released from parasympathetic nerves.1–5 Their role in the unconscious regulation of organ and central nervous system function makes them potential therapeutic targets for a broad spectrum of diseases. The M2 muscarinic acetylcholine receptor (M2 receptor) is essential for the physiologic control of cardiovascular function through activation of G protein-coupled inwardly-rectifying potassium channels, and is of particular interest because of its extensive pharmacological characterization with both orthosteric and allosteric ligands. Here we report the structure of antagonist-bound M2 receptor, the first human acetylcholine receptor to be characterized structurally. The antagonist QNB binds in the middle of a long aqueous channel extending approximately two-thirds through the membrane. The orthosteric binding pocket is formed by amino acids that are identical in all 5 muscarinic receptor subtypes, and shares structural homology with other functionally unrelated acetylcholine binding proteins from different species. A layer of tyrosine residues forms an aromatic cap restricting dissociation of the bound ligand. A binding site for allosteric ligands has been mapped to residues at the entrance to the binding pocket near this aromatic cap. The M2 receptor structure provides insights into the challenges of developing subtype-selective ligands for muscarinic receptors and their propensity for allosteric regulation.

Development of M1 mAChR Allosteric and Bitopic Ligands: Prospective Therapeutics for the Treatment of Cognitive Deficits

“…62 However, recent publication of the inactive human M 2 and the rat M 3 mAChR crystal structures 63,64 will undoubtedly provide unparalleled insight into the structures of the other muscarinic receptor subtypes going forward.…”

Molecular Mechanisms of Methoctramine Binding and Selectivity at Muscarinic Acetylcholine Receptors

“…The structure of methoctramine (CID 4108) was downloaded from the PubChem database (pubchem.ncbi.nlm.nih.gov) and processed with Schrödinger's (Schrödinger LLC, New Portland, OR) LigPrep. Crystal structures of M 2 (Haga et al, 2012) (PDB code 3UON) and M 3 ) (PDB code 4DAJ) receptors were downloaded from the RCSB Protein Data Bank (www. rcsb.org), and were preprocessed with Schrödinger's Protein Preparation Wizard to remove nonreceptor parts, fill missing side chains, and energy minimize structures in the OPLSA 2005 force field.…”

Opioid receptors revealed

“…Now, it seems the flood is approaching. Stevens's and Kobilka's groups each have another structure ready to go, on top of the five GPCRs they have already published this year [4][5][6] . Stevens predicts several more from his lab by the end of the year.…”