Dibasic protein kinase A sites regulate bursting rate and nucleotide sensitivity of the cystic fibrosis transmembrane conductance regulator chloride channel

Ceri J. Mathews, Joseph A. Tabcharani, Xiu-Bao D Chang, Timothy J. Jensen, John R. Riordan, John W. Hanrahan

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Abstract

1. The relationship between phosphorylation of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel and its gating by nucleotides was examined using the patch clamp technique by comparing strongly phosphorylated wild-type (WT) channels with weakly phosphorylated mutant channels lacking four (4SA) or all ten (10SA) dibasic consensus sequences for phosphorylation by protein kinase A (PKA). 2. The open probability (P(o)) of strongly phosphorylated WT channels in excised patches was about twice that of 4SA and 10SA channels, after correcting for tile number of functional channels per patch by addition of adenylylimidodiphosphate (AMP-PNP). The mean burst durations of WT and mutant channels were similar, and therefore the elevated P(o) of WT was due to its higher bursting rate. 3. The ATP dependence of the 10SA mutant was shifted to higher nucleotide concentrations compared with WT channels. The relationship between P(o) and [ATP] was noticeably sigmoid for 10SA channels (Hill coefficient, 1.8), consistent with positive co-operativity between two sites. Increasing ATP concentration to 10 mM caused the P(o) of both WT and 10SA channels to decline. 4. Wild-type and mutant CFTR channels became locked in open bursts when exposed to mixtures of ATP and the non-hydrolysable analogue AMP-PNP. The rate at which the low phosphorylation mutants became locked open was about half that of WT channels, consistent with P(o) being the principal determinant of locking rate in WT and mutant channels. 5. We conclude that phosphorylation at 'weak' PKA sites is sufficient to sustain the interactions between the ATP binding domains that mediate locking by AMP-PNP. Phosphorylation of the strong dibasic PKA sites controls the bursting rate and P(o) of WT channels by increasing the apparent affinity of CFTR for ATP.

Original languageEnglish (US)
Pages (from-to)365-377
Number of pages13
JournalJournal of Physiology
Volume508
Issue number2
DOIs
StatePublished - Apr 15 1998

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Cystic Fibrosis Transmembrane Conductance Regulator
Chloride Channels
Cyclic AMP-Dependent Protein Kinases
Adenylyl Imidodiphosphate
Nucleotides
Adenosine Triphosphate
Phosphorylation
Consensus Sequence
Patch-Clamp Techniques
Sigmoid Colon

ASJC Scopus subject areas

  • Physiology

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Dibasic protein kinase A sites regulate bursting rate and nucleotide sensitivity of the cystic fibrosis transmembrane conductance regulator chloride channel. / Mathews, Ceri J.; Tabcharani, Joseph A.; Chang, Xiu-Bao D; Jensen, Timothy J.; Riordan, John R.; Hanrahan, John W.

In: Journal of Physiology, Vol. 508, No. 2, 15.04.1998, p. 365-377.

Research output: Contribution to journalArticle

Mathews, Ceri J. ; Tabcharani, Joseph A. ; Chang, Xiu-Bao D ; Jensen, Timothy J. ; Riordan, John R. ; Hanrahan, John W. / Dibasic protein kinase A sites regulate bursting rate and nucleotide sensitivity of the cystic fibrosis transmembrane conductance regulator chloride channel. In: Journal of Physiology. 1998 ; Vol. 508, No. 2. pp. 365-377.
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N2 - 1. The relationship between phosphorylation of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel and its gating by nucleotides was examined using the patch clamp technique by comparing strongly phosphorylated wild-type (WT) channels with weakly phosphorylated mutant channels lacking four (4SA) or all ten (10SA) dibasic consensus sequences for phosphorylation by protein kinase A (PKA). 2. The open probability (P(o)) of strongly phosphorylated WT channels in excised patches was about twice that of 4SA and 10SA channels, after correcting for tile number of functional channels per patch by addition of adenylylimidodiphosphate (AMP-PNP). The mean burst durations of WT and mutant channels were similar, and therefore the elevated P(o) of WT was due to its higher bursting rate. 3. The ATP dependence of the 10SA mutant was shifted to higher nucleotide concentrations compared with WT channels. The relationship between P(o) and [ATP] was noticeably sigmoid for 10SA channels (Hill coefficient, 1.8), consistent with positive co-operativity between two sites. Increasing ATP concentration to 10 mM caused the P(o) of both WT and 10SA channels to decline. 4. Wild-type and mutant CFTR channels became locked in open bursts when exposed to mixtures of ATP and the non-hydrolysable analogue AMP-PNP. The rate at which the low phosphorylation mutants became locked open was about half that of WT channels, consistent with P(o) being the principal determinant of locking rate in WT and mutant channels. 5. We conclude that phosphorylation at 'weak' PKA sites is sufficient to sustain the interactions between the ATP binding domains that mediate locking by AMP-PNP. Phosphorylation of the strong dibasic PKA sites controls the bursting rate and P(o) of WT channels by increasing the apparent affinity of CFTR for ATP.

AB - 1. The relationship between phosphorylation of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel and its gating by nucleotides was examined using the patch clamp technique by comparing strongly phosphorylated wild-type (WT) channels with weakly phosphorylated mutant channels lacking four (4SA) or all ten (10SA) dibasic consensus sequences for phosphorylation by protein kinase A (PKA). 2. The open probability (P(o)) of strongly phosphorylated WT channels in excised patches was about twice that of 4SA and 10SA channels, after correcting for tile number of functional channels per patch by addition of adenylylimidodiphosphate (AMP-PNP). The mean burst durations of WT and mutant channels were similar, and therefore the elevated P(o) of WT was due to its higher bursting rate. 3. The ATP dependence of the 10SA mutant was shifted to higher nucleotide concentrations compared with WT channels. The relationship between P(o) and [ATP] was noticeably sigmoid for 10SA channels (Hill coefficient, 1.8), consistent with positive co-operativity between two sites. Increasing ATP concentration to 10 mM caused the P(o) of both WT and 10SA channels to decline. 4. Wild-type and mutant CFTR channels became locked in open bursts when exposed to mixtures of ATP and the non-hydrolysable analogue AMP-PNP. The rate at which the low phosphorylation mutants became locked open was about half that of WT channels, consistent with P(o) being the principal determinant of locking rate in WT and mutant channels. 5. We conclude that phosphorylation at 'weak' PKA sites is sufficient to sustain the interactions between the ATP binding domains that mediate locking by AMP-PNP. Phosphorylation of the strong dibasic PKA sites controls the bursting rate and P(o) of WT channels by increasing the apparent affinity of CFTR for ATP.

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