title: NMR structures of the human α7 nAChR transmembrane domain and associated anesthetic binding sites.
abstract: The α7 nicotinic acetylcholine receptor (nAChR), assembled as homomeric pentameric ligand-gated ion channels, is one of the most abundant nAChR subtypes in the brain. Despite its importance in memory, learning and cognition, no structure has been determined for the α7 nAChR TM domain, a target for allosteric modulators. Using solution state NMR, we determined the structure of the human α7 nAChR TM domain (PDB ID: 2MAW) and demonstrated that the α7 TM domain formed functional channels in Xenopus oocytes. We identified the associated binding sites for the anesthetics halothane and ketamine; the former cannot sensitively inhibit α7 function, but the latter can. The α7 TM domain folds into the expected four-helical bundle motif, but the intra-subunit cavity at the extracellular end of the α7 TM domain is smaller than the equivalent cavity in the α4β2 nAChRs (PDB IDs: 2LLY; 2LM2). Neither drug binds to the extracellular end of the α7 TM domain, but two halothane molecules or one ketamine molecule binds to the intracellular end of the α7 TM domain. Halothane and ketamine binding sites are partially overlapped. Ketamine, but not halothane, perturbed the α7 channel-gate residue L9'. Furthermore, halothane did not induce profound dynamics changes in the α7 channel as observed in α4β2. The study offers a novel high-resolution structure for the human α7 nAChR TM domain that is invaluable for developing α7-specific therapeutics. It also provides evidence to support the hypothesis: only when anesthetic binding perturbs the channel pore or alters the channel motion, can binding generate functional consequences.
authors.affiliation: Department of Anesthesiology, University of Pittsburgh School of Medicine, USA.
authors.forename: Vasyl
authors.initials: V
authors.lastname: Bondarenko
authors.affiliation: Department of Anesthesiology, University of Pittsburgh School of Medicine, USA; Department of Computational & Systems Biology, University of Pittsburgh School of Medicine, USA.
authors.forename: David D
authors.initials: DD
authors.lastname: Mowrey
authors.affiliation: Department of Anesthesiology, University of Pittsburgh School of Medicine, USA.
authors.forename: Tommy S
authors.initials: TS
authors.lastname: Tillman
authors.affiliation: Department of Anesthesiology, University of Pittsburgh School of Medicine, USA.
authors.forename: Edom
authors.initials: E
authors.lastname: Seyoum
authors.affiliation: Department of Anesthesiology, University of Pittsburgh School of Medicine, USA; Department of Structural Biology, University of Pittsburgh School of Medicine, USA; Department of Pharmacology & Chemical Biology, University of Pittsburgh School of Medicine, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Department of Anesthesiology, University of Pittsburgh School of Medicine, USA; Department of Computational & Systems Biology, University of Pittsburgh School of Medicine, USA; Department of Pharmacology & Chemical Biology, University of Pittsburgh School of Medicine, USA. Electronic address: tangp@upmc.edu.
authors.forename: Pei
authors.initials: P
authors.lastname: Tang
mesh_terms: D000777:Anesthetics / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D006221:Halothane / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D007649:Ketamine / Q000737:chemistry / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D013816:Thermodynamics; D014981:Xenopus; D064569:alpha7 Nicotinic Acetylcholine Receptor / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000777:Anesthetics; D008565:Membrane Proteins; D064569:alpha7 Nicotinic Acetylcholine Receptor; D007649:Ketamine; D006221:Halothane
keywords: General anesthetics; Halothane; Ketamine; NMR; Protein dynamics; α7 nAChR structure