title: Structure of the human M2 muscarinic acetylcholine receptor bound to an antagonist.
abstract: The parasympathetic branch of the autonomic nervous system regulates the activity of multiple organ systems. Muscarinic receptors are G-protein-coupled receptors that mediate the response to acetylcholine released from parasympathetic nerves. 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 physiological 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 the antagonist-bound human M2 receptor, the first human acetylcholine receptor to be characterized structurally, to our knowledge. The antagonist 3-quinuclidinyl-benzilate 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 five 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 structure of the M2 receptor provides insights into the challenges of developing subtype-selective ligands for muscarinic receptors and their propensity for allosteric regulation.
authors.affiliation: Department of Life Science, Faculty of Science, Gakushuin University, Mejiro 1-5-1, Tokyo 171-8588, Japan.
authors.forename: Kazuko
authors.initials: K
authors.lastname: Haga
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Kruse
authors.forename: Hidetsugu
authors.initials: H
authors.lastname: Asada
authors.forename: Takami
authors.initials: T
authors.lastname: Yurugi-Kobayashi
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Shiroishi
authors.forename: Cheng
authors.initials: C
authors.lastname: Zhang
authors.forename: William I
authors.initials: WI
authors.lastname: Weis
authors.forename: Tetsuji
authors.initials: T
authors.lastname: Okada
authors.forename: Brian K
authors.initials: BK
authors.lastname: Kobilka
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Haga
authors.forename: Takuya
authors.initials: T
authors.lastname: Kobayashi
mesh_terms: D000109:Acetylcholine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D000110:Acetylcholinesterase / Q000737:chemistry / Q000378:metabolism; D000494:Allosteric Regulation; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism; D018680:Cholinergic Antagonists / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D018360:Crystallography, X-Ray; D019143:Evolution, Molecular; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D011487:Protein Conformation; D011813:Quinuclidinyl Benzilate / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology*; D043585:Receptor, Muscarinic M2 / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014443:Tyrosine / Q000737:chemistry / Q000378:metabolism
chemical_list: C428944:AChBP protein, Lymnaea; D002352:Carrier Proteins; D018680:Cholinergic Antagonists; D008024:Ligands; D043585:Receptor, Muscarinic M2; D014443:Tyrosine; D011813:Quinuclidinyl Benzilate; D000110:Acetylcholinesterase; D000109:Acetylcholine