title: Comparative surface accessibility of a pore-lining threonine residue (T6') in the glycine and GABA(A) receptors.
abstract: The substituted cysteine accessibility method was used to probe the surface exposure of a pore-lining threonine residue (T6') common to both the glycine receptor (GlyR) and gamma-aminobutyric acid, type A receptor (GABA(A)R) chloride channels. This residue lies close to the channel activation gate, the ionic selectivity filter, and the main pore blocker binding site. Despite their high amino acid sequence homologies and common role in conducting chloride ions, recent studies have suggested that the GlyRs and GABA(A)Rs have divergent open state pore structures at the 6' position. When both the human alpha1(T6'C) homomeric GlyR and the rat alpha1(T6'C)beta1(T6'C) heteromeric GABA(A)R were expressed in human embryonic kidney 293 cells, their 6' residue surface accessibilities differed significantly in the closed state. However, when a soluble cysteine-modifying compound was applied in the presence of saturating agonist concentrations, both receptors were locked into the open state. This action was not induced by oxidizing agents in either receptor. These results provide evidence for a conserved pore opening mechanism in anion-selective members of the ligand-gated ion channel family. The results also indicate that the GABA(A)R pore structure at the 6' level may vary between different expression systems.
authors.affiliation: Department of Physiology and Pharmacology, School of Biomedical Sciences, University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Shan
authors.forename: Justine L
authors.initials: JL
authors.lastname: Haddrill
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Lynch
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D003300:Copper / Q000737:chemistry / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism*; D004220:Disulfides / Q000378:metabolism; D004229:Dithiothreitol / Q000737:chemistry / Q000378:metabolism; D005020:Ethyl Methanesulfonate / Q000031:analogs & derivatives* / Q000378:metabolism; D018756:GABA Antagonists / Q000378:metabolism; D005998:Glycine / Q000378:metabolism; D006801:Humans; D007202:Indicators and Reagents / Q000378:metabolism; D008698:Mesylates / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D010618:Phenanthrolines / Q000737:chemistry / Q000378:metabolism; D010852:Picrotoxin / Q000378:metabolism; D021122:Protein Subunits; D051381:Rats; D011963:Receptors, GABA-A / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018009:Receptors, Glycine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D013223:Statistics as Topic; D013439:Sulfhydryl Reagents / Q000378:metabolism; D013912:Threonine / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D003300:Copper; D003545:Cysteine; D004220:Disulfides; D004229:Dithiothreitol; D005020:Ethyl Methanesulfonate; D018756:GABA Antagonists; D005998:Glycine; D007202:Indicators and Reagents; D008698:Mesylates; D010618:Phenanthrolines; D010852:Picrotoxin; D021122:Protein Subunits; D011963:Receptors, GABA-A; D018009:Receptors, Glycine; D013439:Sulfhydryl Reagents; D013912:Threonine; C093171:methanethiosulfonate ethylammonium; C109154:(2-(trimethylammonium)ethyl)methanethiosulfonate