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Role of Charged Residues in the S1–S4 Voltage Sensor of BK Channels

The activation of large conductance Ca(2+)-activated (BK) potassium channels is weakly voltage dependent compared to Shaker and other voltage-gated K(+) (K(V)) channels. Yet BK and K(V) channels share many conserved charged residues in transmembrane segments S1–S4. We mutated these residues individu...

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Autores principales: Ma, Zhongming, Lou, Xing Jian, Horrigan, Frank T.
Formato: Texto
Lenguaje:English
Publicado: The Rockefeller University Press 2006
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2151507/
https://www.ncbi.nlm.nih.gov/pubmed/16505150
http://dx.doi.org/10.1085/jgp.200509421
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author Ma, Zhongming
Lou, Xing Jian
Horrigan, Frank T.
author_facet Ma, Zhongming
Lou, Xing Jian
Horrigan, Frank T.
author_sort Ma, Zhongming
collection PubMed
description The activation of large conductance Ca(2+)-activated (BK) potassium channels is weakly voltage dependent compared to Shaker and other voltage-gated K(+) (K(V)) channels. Yet BK and K(V) channels share many conserved charged residues in transmembrane segments S1–S4. We mutated these residues individually in mSlo1 BK channels to determine their role in voltage gating, and characterized the voltage dependence of steady-state activation (P(o)) and I(K) kinetics (τ(I(K))) over an extended voltage range in 0–50 μM [Ca(2+)](i). mSlo1 contains several positively charged arginines in S4, but only one (R213) together with residues in S2 (D153, R167) and S3 (D186) are potentially voltage sensing based on the ability of charge-altering mutations to reduce the maximal voltage dependence of P(O). The voltage dependence of P(O) and τ(I(K)) at extreme negative potentials was also reduced, implying that the closed–open conformational change and voltage sensor activation share a common source of gating charge. Although the position of charged residues in the BK and K(V) channel sequence appears conserved, the distribution of voltage-sensing residues is not. Thus the weak voltage dependence of BK channel activation does not merely reflect a lack of charge but likely differences with respect to K(V) channels in the position and movement of charged residues within the electric field. Although mutation of most sites in S1–S4 did not reduce gating charge, they often altered the equilibrium constant for voltage sensor activation. In particular, neutralization of R207 or R210 in S4 stabilizes the activated state by 3–7 kcal mol(−1), indicating a strong contribution of non–voltage-sensing residues to channel function, consistent with their participation in state-dependent salt bridge interactions. Mutations in S4 and S3 (R210E, D186A, and E180A) also unexpectedly weakened the allosteric coupling of voltage sensor activation to channel opening. The implications of our findings for BK channel voltage gating and general mechanisms of voltage sensor activation are discussed.
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spelling pubmed-21515072008-01-17 Role of Charged Residues in the S1–S4 Voltage Sensor of BK Channels Ma, Zhongming Lou, Xing Jian Horrigan, Frank T. J Gen Physiol Articles The activation of large conductance Ca(2+)-activated (BK) potassium channels is weakly voltage dependent compared to Shaker and other voltage-gated K(+) (K(V)) channels. Yet BK and K(V) channels share many conserved charged residues in transmembrane segments S1–S4. We mutated these residues individually in mSlo1 BK channels to determine their role in voltage gating, and characterized the voltage dependence of steady-state activation (P(o)) and I(K) kinetics (τ(I(K))) over an extended voltage range in 0–50 μM [Ca(2+)](i). mSlo1 contains several positively charged arginines in S4, but only one (R213) together with residues in S2 (D153, R167) and S3 (D186) are potentially voltage sensing based on the ability of charge-altering mutations to reduce the maximal voltage dependence of P(O). The voltage dependence of P(O) and τ(I(K)) at extreme negative potentials was also reduced, implying that the closed–open conformational change and voltage sensor activation share a common source of gating charge. Although the position of charged residues in the BK and K(V) channel sequence appears conserved, the distribution of voltage-sensing residues is not. Thus the weak voltage dependence of BK channel activation does not merely reflect a lack of charge but likely differences with respect to K(V) channels in the position and movement of charged residues within the electric field. Although mutation of most sites in S1–S4 did not reduce gating charge, they often altered the equilibrium constant for voltage sensor activation. In particular, neutralization of R207 or R210 in S4 stabilizes the activated state by 3–7 kcal mol(−1), indicating a strong contribution of non–voltage-sensing residues to channel function, consistent with their participation in state-dependent salt bridge interactions. Mutations in S4 and S3 (R210E, D186A, and E180A) also unexpectedly weakened the allosteric coupling of voltage sensor activation to channel opening. The implications of our findings for BK channel voltage gating and general mechanisms of voltage sensor activation are discussed. The Rockefeller University Press 2006-03 /pmc/articles/PMC2151507/ /pubmed/16505150 http://dx.doi.org/10.1085/jgp.200509421 Text en Copyright © 2006, 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 Articles
Ma, Zhongming
Lou, Xing Jian
Horrigan, Frank T.
Role of Charged Residues in the S1–S4 Voltage Sensor of BK Channels
title Role of Charged Residues in the S1–S4 Voltage Sensor of BK Channels
title_full Role of Charged Residues in the S1–S4 Voltage Sensor of BK Channels
title_fullStr Role of Charged Residues in the S1–S4 Voltage Sensor of BK Channels
title_full_unstemmed Role of Charged Residues in the S1–S4 Voltage Sensor of BK Channels
title_short Role of Charged Residues in the S1–S4 Voltage Sensor of BK Channels
title_sort role of charged residues in the s1–s4 voltage sensor of bk channels
topic Articles
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2151507/
https://www.ncbi.nlm.nih.gov/pubmed/16505150
http://dx.doi.org/10.1085/jgp.200509421
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