Differentially altered Ca2+ regulation and Ca2+ permeability in Cx26 hemichannels formed by the A40V and G45E mutations that cause keratitis ichthyosis deafness syndrome

Helmuth A. Sánchez, Gülistan Meşe, Miduturu Srinivas, Thomas W. White, Vytautas Verselis

Research output: Contribution to journalArticle

101 Citations (Scopus)

Abstract

Mutations in GJB2, which, encodes Cx26, are one of the most common causes of inherited deafness in humans. More than 100 mutations have been identified scattered throughout the Cx26 protein, most of which cause nonsyndromic sensorineural deafness. In a subset of mutations, deafness is accompanied by hyperkeratotic skin disorders, which are typically severe and sometimes fatal. Many of these syndromic deafness mutations localize to the amino-terminal and first extracellular loop (El) domains. Here, we examined two such mutations, A40V and G45E, which are positioned near the TMl/El boundary and are associated with keratitis ichthyosis deafness (KID) syndrome. Both of these mutants have been reported to form hemichannels that open aberrantly, leading to "leaky" cell membranes. Here, we quantified the Ca2+ sensitivities and examined the biophysical properties of these mutants at macroscopic and single-channel levels. We find that A40V hemichannels show significantly impaired regulation by extracellular Ca2+, increasing the likelihood of aberrant hemichannel opening as previously suggested. However, G45E hemichannels show only modest impairment in regulation by Ca2+ and instead exhibit a substantial increase in permeability to Ca2+. Using cysteine substitution and examination of accessibility to thiolmodifying reagents, we demonstrate that G45, but not A40, is a pore-lining residue. Both mutants function as cellcell channels. The data suggest that G45E and A40V are hemichannel gain-of-function mutants that produce similar phenotypes, but by different; underlying mechanisms. A40V produces leaky hemichannels, whereas G45E provides a route for excessive entry of Ca2+. These aberrant, properties, alone or in combination, can severely compromise cell integrity and lead to increased cell death.

Original languageEnglish (US)
Pages (from-to)47-62
Number of pages16
JournalJournal of General Physiology
Volume136
Issue number1
DOIs
StatePublished - Jul 2010

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Permeability
Deafness
Mutation
Cysteine
Cell Death
Cell Membrane
Keratitis-Ichthyosis-Deafness Syndrome
Phenotype
Skin
Proteins

ASJC Scopus subject areas

  • Physiology
  • Medicine(all)

Cite this

Differentially altered Ca2+ regulation and Ca2+ permeability in Cx26 hemichannels formed by the A40V and G45E mutations that cause keratitis ichthyosis deafness syndrome. / Sánchez, Helmuth A.; Meşe, Gülistan; Srinivas, Miduturu; White, Thomas W.; Verselis, Vytautas.

In: Journal of General Physiology, Vol. 136, No. 1, 07.2010, p. 47-62.

Research output: Contribution to journalArticle

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abstract = "Mutations in GJB2, which, encodes Cx26, are one of the most common causes of inherited deafness in humans. More than 100 mutations have been identified scattered throughout the Cx26 protein, most of which cause nonsyndromic sensorineural deafness. In a subset of mutations, deafness is accompanied by hyperkeratotic skin disorders, which are typically severe and sometimes fatal. Many of these syndromic deafness mutations localize to the amino-terminal and first extracellular loop (El) domains. Here, we examined two such mutations, A40V and G45E, which are positioned near the TMl/El boundary and are associated with keratitis ichthyosis deafness (KID) syndrome. Both of these mutants have been reported to form hemichannels that open aberrantly, leading to {"}leaky{"} cell membranes. Here, we quantified the Ca2+ sensitivities and examined the biophysical properties of these mutants at macroscopic and single-channel levels. We find that A40V hemichannels show significantly impaired regulation by extracellular Ca2+, increasing the likelihood of aberrant hemichannel opening as previously suggested. However, G45E hemichannels show only modest impairment in regulation by Ca2+ and instead exhibit a substantial increase in permeability to Ca2+. Using cysteine substitution and examination of accessibility to thiolmodifying reagents, we demonstrate that G45, but not A40, is a pore-lining residue. Both mutants function as cellcell channels. The data suggest that G45E and A40V are hemichannel gain-of-function mutants that produce similar phenotypes, but by different; underlying mechanisms. A40V produces leaky hemichannels, whereas G45E provides a route for excessive entry of Ca2+. These aberrant, properties, alone or in combination, can severely compromise cell integrity and lead to increased cell death.",
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