title: A highly conserved aspartic acid residue in the signature disulfide loop of the alpha 1 subunit is a determinant of gating in the glycine receptor.
abstract: Ligand-gated ion channels (LGICs) mediate rapid chemical neurotransmission. This gene superfamily includes the nicotinic acetylcholine, GABAA/C, 5-hydroxytryptamine type 3, and glycine receptors. A signature disulfide loop (Cys loop) in the extracellular domain is a structural motif common to all LGIC member subunits. Here we report that a highly conserved aspartic acid residue within the Cys loop at position 148 (Asp-148) of the glycine receptor alpha1 subunit is critical in the process of receptor activation. Mutation of this acidic residue to the basic amino acid lysine produces a large decrease in the potency of glycine, produces a decrease in the Hill slope, and converts taurine from a full agonist to a partial agonist; these data are consistent with a molecular defect in the receptor gating mechanism. Additional mutation of Asp-148 shows that alterations in the EC50 for agonists are dependent upon the charge of the side chain at this position and not molecular volume, polarity, or hydropathy. This study implicates negative charge at position Asp-148 as a critical component of the process in which agonist binding is coupled to channel gating. This finding adds to an emerging body of evidence supporting the involvement of the Cys loop in the gating mechanism of the LGICs.
authors.affiliation: Graduate Program in Neuroscience, Weill Medical College of Cornell University, New York, New York 10021, USA. cms2002@med.cornell.edu
authors.forename: Claude M
authors.initials: CM
authors.lastname: Schofield
authors.forename: Andrew
authors.initials: A
authors.lastname: Jenkins
authors.forename: Neil L
authors.initials: NL
authors.lastname: Harrison
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001224:Aspartic Acid / Q000737:chemistry*; D002460:Cell Line; D002713:Chlorine / Q000494:pharmacology; D003545:Cysteine / Q000737:chemistry; D018076:DNA, Complementary / Q000378:metabolism; D004220:Disulfides; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005822:Genetic Vectors; D005998:Glycine / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels; D008239:Lysine / Q000737:chemistry; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D017434:Protein Structure, Tertiary; D018009:Receptors, Glycine / Q000737:chemistry*; D013654:Taurine / Q000737:chemistry
chemical_list: D018076:DNA, Complementary; D004220:Disulfides; D007473:Ion Channels; D018009:Receptors, Glycine; D013654:Taurine; D001224:Aspartic Acid; D002713:Chlorine; D008239:Lysine; D003545:Cysteine; D005998:Glycine