title: Critical Molecular Determinants of α7 Nicotinic Acetylcholine Receptor Allosteric Activation: SEPARATION OF DIRECT ALLOSTERIC ACTIVATION AND POSITIVE ALLOSTERIC MODULATION.
abstract: The α7 nicotinic acetylcholine receptors (nAChRs) are uniquely sensitive to selective positive allosteric modulators (PAMs), which increase the efficiency of channel activation to a level greater than that of other nAChRs. Although PAMs must work in concert with "orthosteric" agonists, compounds such as GAT107 ((3aR,4S,9bS)-4-(4-bromophenyl)-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinoline-8-sulfonamide) have the combined properties of agonists and PAMs (ago-PAM) and produce very effective channel activation (direct allosteric activation (DAA)) by operating at two distinct sites in the absence of added agonist. One site is likely to be the same transmembrane site where PAMs like PNU-120596 function. We show that the other site, required for direct activation, is likely to be solvent-accessible at the extracellular domain vestibule. We identify key attributes of molecules in this family that are able to act at the DAA site through variation at the aryl ring substituent of the tetrahydroquinoline ring system and with two different classes of competitive antagonists of DAA. Analyses of molecular features of effective allosteric agonists allow us to propose a binding model for the DAA site, featuring a largely non-polar pocket accessed from the extracellular vestibule with an important role for Asp-101. This hypothesis is supported with data from site-directed mutants. Future refinement of the model and the characterization of specific GAT107 analogs will allow us to define critical structural elements that can be mapped onto the receptor surface for an improved understanding of this novel way to target α7 nAChR therapeutically.
authors.affiliation: From the Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200.
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Horenstein
authors.affiliation: the Department of Pharmacology and Therapeutics, University of Florida, Gainesville, Florida 32610-0267, and.
authors.forename: Roger L
authors.initials: RL
authors.lastname: Papke
authors.affiliation: the Department of Pharmaceutical Sciences, School of Pharmacy, Bouvé College of Health Sciences, Northeastern University, Boston, Massachusetts 02115.
authors.forename: Abhijit R
authors.initials: AR
authors.lastname: Kulkarni
authors.affiliation: the Department of Pharmaceutical Sciences, School of Pharmacy, Bouvé College of Health Sciences, Northeastern University, Boston, Massachusetts 02115.
authors.forename: Ganesh U
authors.initials: GU
authors.lastname: Chaturbhuj
authors.affiliation: the Department of Pharmacology and Therapeutics, University of Florida, Gainesville, Florida 32610-0267, and.
authors.forename: Clare
authors.initials: C
authors.lastname: Stokes
authors.affiliation: the Department of Pharmacology and Therapeutics, University of Florida, Gainesville, Florida 32610-0267, and.
authors.forename: Khan
authors.initials: K
authors.lastname: Manther
authors.affiliation: the Department of Pharmaceutical Sciences, School of Pharmacy, Bouvé College of Health Sciences, Northeastern University, Boston, Massachusetts 02115 g.thakur@neu.edu.
authors.forename: Ganesh A
authors.initials: GA
authors.lastname: Thakur
mesh_terms: D000494:Allosteric Regulation; D000495:Allosteric Site; D000595:Amino Acid Sequence; D000818:Animals; D006801:Humans; D007555:Isoxazoles / Q000494:pharmacology; D062105:Molecular Docking Simulation; D008969:Molecular Sequence Data; D018722:Nicotinic Agonists / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D010671:Phenylurea Compounds / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D013449:Sulfonamides / Q000494:pharmacology; D014981:Xenopus; D064569:alpha7 Nicotinic Acetylcholine Receptor / Q000819:agonists / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: C508388:1-(5-chloro-2,4-dimethoxyphenyl)-3-(5-methylisoxazol-3-yl)urea; C578201:4-(4-bromophenyl)-3a,4,5,9b-tetrahydro-3H-cyclopenta(c)quinoline-8-sulfonamide; D007555:Isoxazoles; D018722:Nicotinic Agonists; D010671:Phenylurea Compounds; D011804:Quinolines; D013449:Sulfonamides; D064569:alpha7 Nicotinic Acetylcholine Receptor
keywords: Xenopus; allosteric regulation; ion channel; nicotinic acetylcholine receptors (nAChR); receptor desensitization