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Common mechanism of pore opening shared by five different potassium channels.

ABSTRACT: A fundamental question associated with the function of ion channels is the conformational changes that allow for reversibly opening/occluding the pore through which the cations permeate. The recently elucidated crystal structures of potassium channels reveal similar structural motifs at their pore-forming regions, suggesting that they share a common gating mechanism. The validity of this hypothesis is explored by analyzing the collective dynamics of five known K(+) channel structures. Normal-mode analysis using the Gaussian network model strikingly reveals that all five structures display the same intrinsic motions at their pore-forming region despite the differences in their sequences, structures, and activation mechanisms. Superposition of the most cooperative mode profiles shows that the identified common mechanism is a global corkscrew-like counterrotation of the extracellular and cytoplasmic (CP) regions, leading to the opening of the CP end of the pore. A second cooperative mode shared by all five K(+) channels is the extension of the extracellular and/or CP ends via alternating anticorrelated fluctuations of pairs of diagonally opposite monomers. Residues acting as hinges/anchors in both modes are highly conserved across the members of the family of K(+) channel proteins, consistent with their presently disclosed critical mechanical role in pore gating.

SUBMITTER: Shrivastava IH

PROVIDER: S-EPMC1459499 | biostudies-literature | 2006 Jun

REPOSITORIES: biostudies-literature

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Common mechanism of pore opening shared by five different potassium channels.

Shrivastava Indira H IH Bahar Ivet I

Biophysical journal 20060313 11

A fundamental question associated with the function of ion channels is the conformational changes that allow for reversibly opening/occluding the pore through which the cations permeate. The recently elucidated crystal structures of potassium channels reveal similar structural motifs at their pore-forming regions, suggesting that they share a common gating mechanism. The validity of this hypothesis is explored by analyzing the collective dynamics of five known K(+) channel structures. Normal-mod ...[more]

PMID: 16533848

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Project description:The TWIK-related acid-sensitive potassium channel 3 (TASK-3; KCNK9) tandem pore potassium channel function is activated by halogenated anesthetics through binding at a putative anesthetic-binding cavity. To understand the pharmacologic requirements for TASK-3 activation, we studied the concentration-response of TASK-3 to several anesthetics (isoflurane, desflurane, sevoflurane, halothane, α-chloralose, 2,2,2-trichloroethanol [TCE], and chloral hydrate), to ethanol, and to a panel of halogenated methanes and alcohols. We used mutagenesis to probe the anesthetic-binding cavity as observed in a TASK-3 homology model. TASK-3 activation was quantified by Ussing chamber voltage clamp analysis. We mutagenized the residue Val-136, which lines the anesthetic-binding cavity, its flanking residues (132 to 140), and Leu-122, a pore-gating residue. The 2-halogenated ethanols activate wild-type TASK-3 with the following rank order efficacy (normalized current [95% confidence interval]): 2,2,2-tribromo-(267% [240-294]) > 2,2,2-trichloro-(215% [196-234]) > chloral hydrate (165% [161-176]) > 2,2-dichloro- > 2-chloro ≈ 2,2,2-trifluoroethanol > ethanol. Similarly, carbon tetrabromide (296% [245-346]), carbon tetrachloride (180% [163-196]), and 1,1,1,3,3,3-hexafluoropropanol (200% [194-206]) activate TASK-3, whereas the larger carbon tetraiodide and α-chloralose inhibit. Clinical agents activate TASK-3 with the following rank order efficacy: halothane (207% [202-212]) > isoflurane (169% [161-176]) > sevoflurane (164% [150-177]) > desflurane (119% [109-129]). Mutations at and near residue-136 modify TCE activation of TASK-3, and interestingly M159W, V136E, and L122D were resistant to both isoflurane and TCE activation. TASK-3 function is activated by a multiple agents and requires a halogenated substituent between ∼30 and 232 cm3/mol volume with potency increased by halogen polarizeability. Val-136 and adjacent residues may mediate anesthetic binding and stabilize an open state regulated by pore residue Leu-122. Isoflurane and TCE likely share commonalities in their mechanism of TASK-3 activation.

Project description:BackgroundHypoxia-ischemia predisposes to atrial arrhythmia. Atrial ATP-sensitive potassium channel (KATP) modulation during hypoxia has not been explored. We investigated the effects of hypoxia on atrial electrophysiology in mice with global deletion of KATP pore-forming subunits.MethodsWhole heart KATP RNA expression was probed. Whole-cell KATP current and action potentials were recorded in isolated wild-type (WT), Kir6.1 global knockout (6.1-gKO), and Kir6.2 global knockout (6.2-gKO) murine atrial myocytes. Langendorff-perfused hearts were assessed for atrial effective refractory period (ERP), conduction velocity, wavefront path length (WFPL), and arrhymogenicity under normoxia/hypoxia using a microelectrode array and programmed electrical stimulation. Heart histology was assessed.ResultsExpression patterns were essentially identical for all KATP subunit RNA across human heart, whereas in mouse, Kir6.1 and SUR2 (sulphonylurea receptor subunit) were higher in ventricle than atrium, and Kir6.2 and SUR1 were higher in atrium. Compared with WT, 6.2-gKO atrial myocytes had reduced tolbutamide-sensitive current and action potentials were more depolarized with slower upstroke and reduced peak amplitude. Action potential duration was prolonged in 6.1-gKO atrial myocytes, absent of changes in other ion channel gene expression or atrial myocyte hypertrophy. In Langendorff-perfused hearts, baseline atrial ERP was prolonged and conduction velocity reduced in both KATP knockout mice compared with WT, without histological fibrosis. Compared with baseline, hypoxia led to conduction velocity slowing, stable ERP, and WFPL shortening in WT and 6.1-gKO hearts, whereas WFPL was stable in 6.2-gKO hearts due to ERP prolongation with conduction velocity slowing. Tolbutamide reversed hypoxia-induced WFPL shortening in WT and 6.1-gKO hearts through ERP prolongation. Atrial tachyarrhythmias inducible with programmed electrical stimulation during hypoxia in WT and 6.1-gKO mice correlated with WFPL shortening. Spontaneous arrhythmia was not seen.ConclusionsKATP block/absence leads to cellular and tissue level atrial electrophysiological modification. Kir6.2 global knockout prevents hypoxia-induced atrial WFPL shortening and atrial arrhythmogenicity to programmed electrical stimulation. This mechanism could be explored translationally to treat ischemically driven atrial arrhythmia.

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Common mechanism of pore opening shared by five different potassium channels.

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Common mechanism of pore opening shared by five different potassium channels.

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