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On the Molecular Basis of Ion Permeation in the Epithelial Na(+) Channel
The epithelial Na(+) channel (ENaC) is highly selective for Na(+) and Li(+) over K(+) and is blocked by the diuretic amiloride. ENaC is a heterotetramer made of two α, one β, and one γ homologous subunits, each subunit comprising two transmembrane segments. Amino acid residues involved in binding of...
Autores principales: | , , , , |
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Formato: | Texto |
Lenguaje: | English |
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The Rockefeller University Press
1999
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2229642/ https://www.ncbi.nlm.nih.gov/pubmed/10398689 |
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author | Kellenberger, Stephan Hoffmann-Pochon, Nicole Gautschi, Ivan Schneeberger, Estelle Schild, Laurent |
author_facet | Kellenberger, Stephan Hoffmann-Pochon, Nicole Gautschi, Ivan Schneeberger, Estelle Schild, Laurent |
author_sort | Kellenberger, Stephan |
collection | PubMed |
description | The epithelial Na(+) channel (ENaC) is highly selective for Na(+) and Li(+) over K(+) and is blocked by the diuretic amiloride. ENaC is a heterotetramer made of two α, one β, and one γ homologous subunits, each subunit comprising two transmembrane segments. Amino acid residues involved in binding of the pore blocker amiloride are located in the pre-M2 segment of β and γ subunits, which precedes the second putative transmembrane α helix (M2). A residue in the α subunit (αS589) at the NH(2) terminus of M2 is critical for the molecular sieving properties of ENaC. ENaC is more permeable to Li(+) than Na(+) ions. The concentration of half-maximal unitary conductance is 38 mM for Na(+) and 118 mM for Li(+), a kinetic property that can account for the differences in Li(+) and Na(+) permeability. We show here that mutation of amino acid residues at homologous positions in the pre-M2 segment of α, β, and γ subunits (αG587, βG529, γS541) decreases the Li(+)/Na(+) selectivity by changing the apparent channel affinity for Li(+) and Na(+). Fitting single-channel data of the Li(+) permeation to a discrete-state model including three barriers and two binding sites revealed that these mutations increased the energy needed for the translocation of Li(+) from an outer ion binding site through the selectivity filter. Mutation of βG529 to Ser, Cys, or Asp made ENaC partially permeable to K(+) and larger ions, similar to the previously reported αS589 mutations. We conclude that the residues αG587 to αS589 and homologous residues in the β and γ subunits form the selectivity filter, which tightly accommodates Na(+) and Li(+) ions and excludes larger ions like K(+). |
format | Text |
id | pubmed-2229642 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 1999 |
publisher | The Rockefeller University Press |
record_format | MEDLINE/PubMed |
spelling | pubmed-22296422008-04-22 On the Molecular Basis of Ion Permeation in the Epithelial Na(+) Channel Kellenberger, Stephan Hoffmann-Pochon, Nicole Gautschi, Ivan Schneeberger, Estelle Schild, Laurent J Gen Physiol Original Article The epithelial Na(+) channel (ENaC) is highly selective for Na(+) and Li(+) over K(+) and is blocked by the diuretic amiloride. ENaC is a heterotetramer made of two α, one β, and one γ homologous subunits, each subunit comprising two transmembrane segments. Amino acid residues involved in binding of the pore blocker amiloride are located in the pre-M2 segment of β and γ subunits, which precedes the second putative transmembrane α helix (M2). A residue in the α subunit (αS589) at the NH(2) terminus of M2 is critical for the molecular sieving properties of ENaC. ENaC is more permeable to Li(+) than Na(+) ions. The concentration of half-maximal unitary conductance is 38 mM for Na(+) and 118 mM for Li(+), a kinetic property that can account for the differences in Li(+) and Na(+) permeability. We show here that mutation of amino acid residues at homologous positions in the pre-M2 segment of α, β, and γ subunits (αG587, βG529, γS541) decreases the Li(+)/Na(+) selectivity by changing the apparent channel affinity for Li(+) and Na(+). Fitting single-channel data of the Li(+) permeation to a discrete-state model including three barriers and two binding sites revealed that these mutations increased the energy needed for the translocation of Li(+) from an outer ion binding site through the selectivity filter. Mutation of βG529 to Ser, Cys, or Asp made ENaC partially permeable to K(+) and larger ions, similar to the previously reported αS589 mutations. We conclude that the residues αG587 to αS589 and homologous residues in the β and γ subunits form the selectivity filter, which tightly accommodates Na(+) and Li(+) ions and excludes larger ions like K(+). The Rockefeller University Press 1999-07-01 /pmc/articles/PMC2229642/ /pubmed/10398689 Text en © 1999 The Rockefeller University Press This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/4.0/). |
spellingShingle | Original Article Kellenberger, Stephan Hoffmann-Pochon, Nicole Gautschi, Ivan Schneeberger, Estelle Schild, Laurent On the Molecular Basis of Ion Permeation in the Epithelial Na(+) Channel |
title | On the Molecular Basis of Ion Permeation in the Epithelial Na(+) Channel |
title_full | On the Molecular Basis of Ion Permeation in the Epithelial Na(+) Channel |
title_fullStr | On the Molecular Basis of Ion Permeation in the Epithelial Na(+) Channel |
title_full_unstemmed | On the Molecular Basis of Ion Permeation in the Epithelial Na(+) Channel |
title_short | On the Molecular Basis of Ion Permeation in the Epithelial Na(+) Channel |
title_sort | on the molecular basis of ion permeation in the epithelial na(+) channel |
topic | Original Article |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2229642/ https://www.ncbi.nlm.nih.gov/pubmed/10398689 |
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