Click here to close
Hello! We notice that you are using Internet Explorer, which is not supported by Xenbase and may cause the site to display incorrectly.
We suggest using a current version of Chrome,
FireFox, or Safari.
In glycine and GABA(A) channels, different subunits contribute asymmetrically to channel conductance via residues in the extracellular domain.
Moroni M, Meyer JO, Lahmann C, Sivilotti LG.
???displayArticle.abstract???
Single-channel conductance in Cys-loop channels is controlled by the nature of the amino acids in the narrowest parts of the ion conduction pathway, namely the second transmembrane domain (M2) and the intracellular helix. In cationic channels, such as Torpedo ACh nicotinic receptors, conductance is increased by negatively charged residues exposed to the extracellular vestibule. We now show that positively charged residues at the same loop 5 position boost also the conductance of anionic Cys-loop channels, such as glycine (α1 and α1β) and GABA(A) (α1β2γ2) receptors. Charge reversal mutations here produce a greater decrease on outward conductance, but their effect strongly depends on which subunit carries the mutation. In the glycine α1β receptor, replacing Lys with Glu in α1 reduces single-channel conductance by 41%, but has no effect in the β subunit. By expressing concatameric receptors with constrained stoichiometry, we show that this asymmetry is not explained by the subunit copy number. A similar pattern is observed in the α1β2γ2 GABA(A) receptor, where only mutations in α1 or β2 decreased conductance (to different extents). In both glycine and GABA receptors, the effect of mutations in different subunits does not sum linearly: mutations that had no detectable effect in isolation did enhance the effect of mutations carried by other subunits. As in the nicotinic receptor, charged residues in the extracellular vestibule of anionic Cys-loop channels influence elementary conductance. The size of this effect strongly depends on the direction of the ion flow and, unexpectedly, on the nature of the subunit that carries the residue.
Béhé,
Determination of NMDA NR1 subunit copy number in recombinant NMDA receptors.
1995, Pubmed,
Xenbase
Béhé,
Determination of NMDA NR1 subunit copy number in recombinant NMDA receptors.
1995,
Pubmed
,
Xenbase Bocquet,
X-ray structure of a pentameric ligand-gated ion channel in an apparently open conformation.
2009,
Pubmed Bormann,
Mechanism of anion permeation through channels gated by glycine and gamma-aminobutyric acid in mouse cultured spinal neurones.
1987,
Pubmed Bormann,
Residues within transmembrane segment M2 determine chloride conductance of glycine receptor homo- and hetero-oligomers.
1993,
Pubmed Brams,
Crystal structures of a cysteine-modified mutant in loop D of acetylcholine-binding protein.
2011,
Pubmed Burzomato,
Stoichiometry of recombinant heteromeric glycine receptors revealed by a pore-lining region point mutation.
2003,
Pubmed Carland,
Characterization of the effects of charged residues in the intracellular loop on ion permeation in alpha1 glycine receptor channels.
2009,
Pubmed Chang,
Stoichiometry of a recombinant GABAA receptor.
1996,
Pubmed
,
Xenbase Cooper,
Pentameric structure and subunit stoichiometry of a neuronal nicotinic acetylcholine receptor.
1991,
Pubmed Dalziel,
Mutating the highly conserved second membrane-spanning region 9' leucine residue in the alpha(1) or beta(1) subunit produces subunit-specific changes in the function of human alpha(1)beta(1) gamma-aminobutyric Acid(A) receptors.
2000,
Pubmed Dellisanti,
Crystal structure of the extracellular domain of nAChR alpha1 bound to alpha-bungarotoxin at 1.94 A resolution.
2007,
Pubmed Gonzales,
Stoichiometric analysis of the TM2 6' phenylalanine mutation on desensitization in alpha1beta2 and alpha1beta2gamma2 GABA A receptors.
2008,
Pubmed Groot-Kormelink,
Incomplete incorporation of tandem subunits in recombinant neuronal nicotinic receptors.
2004,
Pubmed
,
Xenbase Groot-Kormelink,
Formation of functional alpha3beta4alpha5 human neuronal nicotinic receptors in Xenopus oocytes: a reporter mutation approach.
2001,
Pubmed
,
Xenbase Groot-Kormelink,
Achieving optimal expression for single channel recording: a plasmid ratio approach to the expression of alpha 1 glycine receptors in HEK293 cells.
2002,
Pubmed Grudzinska,
The beta subunit determines the ligand binding properties of synaptic glycine receptors.
2005,
Pubmed Hansen,
An ion selectivity filter in the extracellular domain of Cys-loop receptors reveals determinants for ion conductance.
2008,
Pubmed Hilf,
Structure of a potentially open state of a proton-activated pentameric ligand-gated ion channel.
2009,
Pubmed Imoto,
Rings of negatively charged amino acids determine the acetylcholine receptor channel conductance.
1988,
Pubmed
,
Xenbase Imoto,
A ring of uncharged polar amino acids as a component of channel constriction in the nicotinic acetylcholine receptor.
1991,
Pubmed
,
Xenbase Jensen,
The beta subunit determines the ion selectivity of the GABAA receptor.
2002,
Pubmed Kelley,
A cytoplasmic region determines single-channel conductance in 5-HT3 receptors.
2003,
Pubmed Keramidas,
Ligand-gated ion channels: mechanisms underlying ion selectivity.
2004,
Pubmed Kienker,
Conductance mutations of the nicotinic acetylcholine receptor do not act by a simple electrostatic mechanism.
1994,
Pubmed
,
Xenbase Konno,
Rings of anionic amino acids as structural determinants of ion selectivity in the acetylcholine receptor channel.
1991,
Pubmed
,
Xenbase Kuhse,
Assembly of the inhibitory glycine receptor: identification of amino acid sequence motifs governing subunit stoichiometry.
1993,
Pubmed
,
Xenbase Langosch,
Conserved quaternary structure of ligand-gated ion channels: the postsynaptic glycine receptor is a pentamer.
1988,
Pubmed Liu,
Subunit stoichiometry of cyclic nucleotide-gated channels and effects of subunit order on channel function.
1996,
Pubmed Meltzer,
Nicotinic acetylcholine receptor channel electrostatics determined by diffusion-enhanced luminescence energy transfer.
2006,
Pubmed Minier,
Techniques: Use of concatenated subunits for the study of ligand-gated ion channels.
2004,
Pubmed Mortensen,
Distinct activities of GABA agonists at synaptic- and extrasynaptic-type GABAA receptors.
2010,
Pubmed Premkumar,
Stoichiometry of recombinant N-methyl-D-aspartate receptor channels inferred from single-channel current patterns.
1997,
Pubmed
,
Xenbase Rayes,
Number and locations of agonist binding sites required to activate homomeric Cys-loop receptors.
2009,
Pubmed Shan,
Asymmetric contribution of alpha and beta subunits to the activation of alphabeta heteromeric glycine receptors.
2003,
Pubmed Sieghart,
Subunit composition, distribution and function of GABA(A) receptor subtypes.
2002,
Pubmed Song,
Role of acetylcholine receptor domains in ion selectivity.
2009,
Pubmed Unwin,
Refined structure of the nicotinic acetylcholine receptor at 4A resolution.
2005,
Pubmed Villarroel,
Location of a threonine residue in the alpha-subunit M2 transmembrane segment that determines the ion flow through the acetylcholine receptor channel.
1991,
Pubmed
,
Xenbase Villarroel,
Asymmetry of the rat acetylcholine receptor subunits in the narrow region of the pore.
1992,
Pubmed Wilkins,
Identification of a beta subunit TM2 residue mediating proton modulation of GABA type A receptors.
2002,
Pubmed Zhou,
Human alpha4beta2 acetylcholine receptors formed from linked subunits.
2003,
Pubmed
,
Xenbase
