Bondarenko_2014_Biochim.Biophys.Acta_1838_1389

The alpha7 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 alpha7 nAChR TM domain, a target for allosteric modulators. Using solution state NMR, we determined the structure of the human alpha7 nAChR TM domain (PDB ID: 2MAW) and demonstrated that the alpha7 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 alpha7 function, but the latter can. The alpha7 TM domain folds into the expected four-helical bundle motif, but the intra-subunit cavity at the extracellular end of the alpha7 TM domain is smaller than the equivalent cavity in the alpha4beta2 nAChRs (PDB IDs: 2LLY; 2LM2). Neither drug binds to the extracellular end of the alpha7 TM domain, but two halothane molecules or one ketamine molecule binds to the intracellular end of the alpha7 TM domain. Halothane and ketamine binding sites are partially overlapped. Ketamine, but not halothane, perturbed the alpha7 channel-gate residue L9'. Furthermore, halothane did not induce profound dynamics changes in the alpha7 channel as observed in alpha4beta2. The study offers a novel high-resolution structure for the human alpha7 nAChR TM domain that is invaluable for developing alpha7-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.