title: A perturbed pK(a) at the binding site of the nicotinic acetylcholine receptor: implications for nicotine binding.
abstract: A series of tethered quaternary ammonium derivatives of Tyr have been incorporated into the binding site of the nicotinic acetylcholine receptor (nAChR) using the in vivo nonsense suppression method, producing constitutively active (self-gating) receptors. We have incorporated primary, secondary, and tertiary amine tethered agonists to give receptors whose constitutive activity can be modulated by pH. Lowering the pH protonates the tethered amine, giving it a positive charge and allowing it to reversibly activate the receptor. Tertiary and secondary tethered amines, TyrO3T and TyrO3S, have been successfully incorporated at alpha149 in the nAChR. Constitutive currents at pH 5.5 are 6 times those at pH 9.0. The pKa of TyrO3T in the binding site appears to be 6 or lower, differing substantially from its pKa in solution ( approximately 9.3). This local pKa perturbation has substantial implications for pharmacological research on the nAChR: of the tertiary agonists considered, noracetylcholine experiences this pKa perturbation, while nicotine does not.
authors.affiliation: Division of Chemistry and Chemical Engineering, Division of Biology, California Institute of Technology, Pasadena 91125, USA.
authors.forename: E James
authors.initials: EJ
authors.lastname: Petersson
authors.forename: Anita
authors.initials: A
authors.lastname: Choi
authors.forename: David S
authors.initials: DS
authors.lastname: Dahan
authors.forename: Henry A
authors.initials: HA
authors.lastname: Lester
authors.forename: Dennis A
authors.initials: DA
authors.lastname: Dougherty
mesh_terms: D000818:Animals; D001665:Binding Sites; D007700:Kinetics; D008958:Models, Molecular; D009538:Nicotine / Q000737:chemistry / Q000378:metabolism*; D018722:Nicotinic Agonists / Q000737:chemistry* / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000737:chemistry / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; D009538:Nicotine