NMR structures of the human α7 nAChR transmembrane domain and associated anesthetic binding sites

https://doi.org/10.1016/j.bbamem.2013.12.018Get rights and content
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Highlights

  • The NMR structure of the human α7 nAChR TM domain (TMD) was determined.

  • Intra-subunit anesthetic binding sites were found at the IC end of the TMD by NMR.

  • Ketamine but not halothane binding perturbed the channel gate residue L9′.

  • Whether binding perturbs the channel gate correlates with the functional effect.

  • The α7 structure is invaluable for designing α7-specific therapeutics.

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.

Keywords

α7 nAChR structure
Halothane
Ketamine
General anesthetics
NMR
Protein dynamics

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