title: Architecture of the neuronal nicotinic acetylcholine receptor ion channel at the binding site of bis-ammonium blockers.
abstract: Structure-activity relationships of 56 pentamethylenbis-ammonium compounds, the blockers of the neuronal nicotinic acetylcholine receptor (nAChR) ion channel, have been studied to estimate the cross-sectional dimensions of the channel pore. The cat superior cervical sympathetic ganglion in situ and isolated guinea pig ileum were used to evaluate the potency of the compounds to block ganglionic transmission. Minimum-energy conformations of each compound were calculated by the molecular mechanics method. A topographic model of the binding site of the blockers was proposed. It incorporates two narrowings, a large and a small one. The small narrowing is located between the large one and the cytoplasmic end of the pore. The cross-sectional dimensions of the large and small narrowings estimated from the dimensions of the blockers are 6.1 x 8.3 A and 5.5 x 6.4 A, respectively, the distance between the narrowings along the pore being approximately 7 A. Most potent blockers would occlude the pore via binding to the channel at the levels of both narrowings. Less potent blockers are either too large or too small to bind to both narrowings simultaneously: large blockers would occlude the pore at the level of large narrowing, while small blockers would pass the large narrowing and occlude the pore at the level of small narrowing only. A comparison of the topographic model with a molecular five-helix bundle model of nAChR pore predicts Serine and Threonine rings to be the most probable candidates for the large and small narrowings, respectively.
authors.affiliation: Schenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, Thorez pr-44, St. Petersburg 194223, Russia.
authors.forename: N B
authors.initials: NB
authors.lastname: Brovtsyna
authors.forename: D B
authors.initials: DB
authors.lastname: Tikhonov
authors.forename: O B
authors.initials: OB
authors.lastname: Gorbunova
authors.forename: V E
authors.initials: VE
authors.lastname: Gmiro
authors.forename: S E
authors.initials: SE
authors.lastname: Serduk
authors.forename: N Y
authors.initials: NY
authors.lastname: Lukomskaya
authors.forename: L G
authors.initials: LG
authors.lastname: Magazanik
authors.forename: B S
authors.initials: BS
authors.lastname: Zhorov
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D008725:Bis-Trimethylammonium Compounds / Q000378:metabolism / Q000494:pharmacology*; D002415:Cats; D002645:Chickens; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects; D007473:Ion Channels / Q000737:chemistry* / Q000187:drug effects; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000187:drug effects; D011487:Protein Conformation; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000187:drug effects; D012694:Serine / Q000737:chemistry; D013329:Structure-Activity Relationship; D017783:Superior Cervical Ganglion / Q000187:drug effects; D013912:Threonine / Q000737:chemistry; D014101:Torpedo
chemical_list: D008725:Bis-Trimethylammonium Compounds; D007473:Ion Channels; D009419:Nerve Tissue Proteins; D000644:Quaternary Ammonium Compounds; D011978:Receptors, Nicotinic; D013912:Threonine; D012694:Serine; C014147:pentamethonium