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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
.
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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.
Bocquet,
X-ray structure of a pentameric ligand-gated ion channel in an apparently open conformation.
2009, Pubmed
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
Béhé,
Determination of NMDA NR1 subunit copy number in recombinant NMDA receptors.
1995,
Pubmed
,
Xenbase
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,
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
Groot-Kormelink,
Incomplete incorporation of tandem subunits in recombinant neuronal nicotinic receptors.
2004,
Pubmed
,
Xenbase
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
