title: Binding of N-methylscopolamine to the extracellular domain of muscarinic acetylcholine receptors.
abstract: Interaction of orthosteric ligands with extracellular domain was described at several aminergic G protein-coupled receptors, including muscarinic acetylcholine receptors. The orthosteric antagonists quinuclidinyl benzilate (QNB) and N-methylscopolamine (NMS) bind to the binding pocket of the muscarinic acetylcholine receptor formed by transmembrane α-helices. We show that high concentrations of either QNB or NMS slow down dissociation of their radiolabeled species from all five subtypes of muscarinic acetylcholine receptors, suggesting allosteric binding. The affinity of NMS at the allosteric site is in the micromolar range for all receptor subtypes. Using molecular modelling of the M2receptor we found that E172 and E175 in the second extracellular loop and N419 in the third extracellular loop are involved in allosteric binding of NMS. Mutation of these amino acids to alanine decreased affinity of NMS for the allosteric binding site confirming results of molecular modelling. The allosteric binding site of NMS overlaps with the binding site of some allosteric, ectopic and bitopic ligands. Understanding of interactions of NMS at the allosteric binding site is essential for correct analysis of binding and action of these ligands.
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 14220 Prague, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Jakubík
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 14220 Prague, Czech Republic.
authors.forename: Alena
authors.initials: A
authors.lastname: Randáková
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 14220 Prague, Czech Republic.
authors.forename: Pavel
authors.initials: P
authors.lastname: Zimčík
authors.affiliation: Department of Experimental and Clinical Pharmacology, University of Minnesota College of Pharmacy, Minneapolis, MN 55455, USA (EEE).
authors.forename: Esam E
authors.initials: EE
authors.lastname: El-Fakahany
authors.affiliation: Institute of Physiology, Czech Academy of Sciences, 14220 Prague, Czech Republic.
authors.forename: Vladimír
authors.initials: V
authors.lastname: Doležal
mesh_terms: D000054:Acceleration; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D007700:Kinetics; D008024:Ligands; D008954:Models, Biological; D056004:Molecular Dynamics Simulation; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D019832:N-Methylscopolamine / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D000072417:Protein Domains; D017433:Protein Structure, Secondary; D011976:Receptors, Muscarinic / Q000737:chemistry* / Q000378:metabolism*; D014316:Tritium / Q000378:metabolism
chemical_list: D008024:Ligands; D050505:Mutant Proteins; D011976:Receptors, Muscarinic; D014316:Tritium; D019832:N-Methylscopolamine