title: Structural basis for alcohol modulation of a pentameric ligand-gated ion channel.
abstract: Despite its long history of use and abuse in human culture, the molecular basis for alcohol action in the brain is poorly understood. The recent determination of the atomic-scale structure of GLIC, a prokaryotic member of the pentameric ligand-gated ion channel (pLGIC) family, provides a unique opportunity to characterize the structural basis for modulation of these channels, many of which are alcohol targets in brain. We observed that GLIC recapitulates bimodal modulation by n-alcohols, similar to some eukaryotic pLGICs: methanol and ethanol weakly potentiated proton-activated currents in GLIC, whereas n-alcohols larger than ethanol inhibited them. Mapping of residues important to alcohol modulation of ionotropic receptors for glycine, γ-aminobutyric acid, and acetylcholine onto GLIC revealed their proximity to transmembrane cavities that may accommodate one or more alcohol molecules. Site-directed mutations in the pore-lining M2 helix allowed the identification of four residues that influence alcohol potentiation, with the direction of their effects reflecting α-helical structure. At one of the potentiation-enhancing residues, decreased side chain volume converted GLIC into a highly ethanol-sensitive channel, comparable to its eukaryotic relatives. Covalent labeling of M2 positions with an alcohol analog, a methanethiosulfonate reagent, further implicated residues at the extracellular end of the helix in alcohol binding. Molecular dynamics simulations elucidated the structural consequences of a potentiation-enhancing mutation and suggested a structural mechanism for alcohol potentiation via interaction with a transmembrane cavity previously termed the "linking tunnel." These results provide a unique structural model for independent potentiating and inhibitory interactions of n-alcohols with a pLGIC family member.
authors: Waggoner Center for Alcohol and Addiction Research, University of Texas at Austin, Austin, TX 78712, USA. reba@mail.utexas.edu
authors: Rebecca J
authors: RJ
authors: Howard
authors: Samuel
authors: S
authors: Murail
authors: Kathryn E
authors: KE
authors: Ondricek
authors: Pierre-Jean
authors: PJ
authors: Corringer
authors: Erik
authors: E
authors: Lindahl
authors: James R
authors: JR
authors: Trudell
authors: R Adron
authors: RA
authors: Harris
mesh_terms: D000438:Alcohols / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics*; D004357:Drug Synergism; D058446:Ligand-Gated Ion Channels / Q000235:genetics* / Q000378:metabolism*; D008698:Mesylates; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000378:metabolism; D011487:Protein Conformation; D016415:Sequence Alignment; D014982:Xenopus laevis
chemical_list: D000438:Alcohols; D001426:Bacterial Proteins; D058446:Ligand-Gated Ion Channels; D008698:Mesylates; C074502:methanethiosulfonate