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

Haga K, Kruse AC, Asada H, Yurugi-Kobayashi T, Shiroishi M, Zhang C, Weis WI, Okada T, Kobilka BK, Haga T, Kobayashi T - Nature (2012)

Bottom Line: 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 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Science, Faculty of Science, Gakushuin University, Mejiro 1-5-1, Tokyo 171-8588, Japan.

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.

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The M2 receptor (blue ribbon) with bound QNB (orange spheres). a, M2 receptor in profile. b, Cytoplasmic surface showing conserved DRY residues in TM3. c, Extracellular view into QNB binding pocket. d, Extracellular view with solvent-accessible surface rendering shows a funnel-shaped vestibule and a nearly buried QNB binding pocket. e, Aqueous channel (green) extending from the extracellular surface into the transmembrane core is interrupted by a layer of three hydrophobic residues (blue spheres). Well-ordered water molecules are shown as red dots.
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Figure 1: The M2 receptor (blue ribbon) with bound QNB (orange spheres). a, M2 receptor in profile. b, Cytoplasmic surface showing conserved DRY residues in TM3. c, Extracellular view into QNB binding pocket. d, Extracellular view with solvent-accessible surface rendering shows a funnel-shaped vestibule and a nearly buried QNB binding pocket. e, Aqueous channel (green) extending from the extracellular surface into the transmembrane core is interrupted by a layer of three hydrophobic residues (blue spheres). Well-ordered water molecules are shown as red dots.

Mentions: The overall structure of the M2 receptor (Fig. 1a) is similar to that of rhodopsin and other recently crystallized inactive GPCR structures (compared in Supplementary Figure 3). The cytoplasmic surface of the M2 receptor is in an inactive conformation, but as with most other GPCR structures, there is no interaction involving Arg1213.50 in the conserved E/DRY sequence in TM3 and Glu3826.30 in TM6 (Fig. 1b). Instead, the Arg1213.50 side chain forms a salt bridge only with Asp1203.49. In rhodopsin, the homologous residues form part of a charge-charge interaction that stabilizes the cytoplasmic ends of TM3 and TM6 in an inactive state17. The second intracellular loop shows a helical conformation similar to that first seen for the turkey β1 adrenergic receptor18.


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

Haga K, Kruse AC, Asada H, Yurugi-Kobayashi T, Shiroishi M, Zhang C, Weis WI, Okada T, Kobilka BK, Haga T, Kobayashi T - Nature (2012)

The M2 receptor (blue ribbon) with bound QNB (orange spheres). a, M2 receptor in profile. b, Cytoplasmic surface showing conserved DRY residues in TM3. c, Extracellular view into QNB binding pocket. d, Extracellular view with solvent-accessible surface rendering shows a funnel-shaped vestibule and a nearly buried QNB binding pocket. e, Aqueous channel (green) extending from the extracellular surface into the transmembrane core is interrupted by a layer of three hydrophobic residues (blue spheres). Well-ordered water molecules are shown as red dots.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3345277&req=5

Figure 1: The M2 receptor (blue ribbon) with bound QNB (orange spheres). a, M2 receptor in profile. b, Cytoplasmic surface showing conserved DRY residues in TM3. c, Extracellular view into QNB binding pocket. d, Extracellular view with solvent-accessible surface rendering shows a funnel-shaped vestibule and a nearly buried QNB binding pocket. e, Aqueous channel (green) extending from the extracellular surface into the transmembrane core is interrupted by a layer of three hydrophobic residues (blue spheres). Well-ordered water molecules are shown as red dots.
Mentions: The overall structure of the M2 receptor (Fig. 1a) is similar to that of rhodopsin and other recently crystallized inactive GPCR structures (compared in Supplementary Figure 3). The cytoplasmic surface of the M2 receptor is in an inactive conformation, but as with most other GPCR structures, there is no interaction involving Arg1213.50 in the conserved E/DRY sequence in TM3 and Glu3826.30 in TM6 (Fig. 1b). Instead, the Arg1213.50 side chain forms a salt bridge only with Asp1203.49. In rhodopsin, the homologous residues form part of a charge-charge interaction that stabilizes the cytoplasmic ends of TM3 and TM6 in an inactive state17. The second intracellular loop shows a helical conformation similar to that first seen for the turkey β1 adrenergic receptor18.

Bottom Line: 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 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Life Science, Faculty of Science, Gakushuin University, Mejiro 1-5-1, Tokyo 171-8588, Japan.

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.

Show MeSH
Related in: MedlinePlus