Voltage-dependent dynamics of the BK channel cytosolic gating ring are coupled to the membrane-embedded voltage sensor

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Abstract

In human large conductance voltage- and calcium-dependent potassium (BK) channels are regulated allosterically by transmembrane voltage and intracellular Ca²⁺. Divalent cation binding sites reside within the gating ring formed by two Regulator of Conductance of Potassium (RCK) domains per subunit. Using patch-clamp fluorometry, we show that Ca²⁺ binding to the RCK1 domain triggers gating ring rearrangements that depend on transmembrane voltage. Because the gating ring is outside the electric field, this voltage sensitivity must originate from coupling to the voltage-dependent channel opening, the voltage sensor or both. Here we demonstrate that alterations of the voltage sensor, either by mutagenesis or regulation by auxiliary subunits, are paralleled by changes in the voltage dependence of the gating ring movements, whereas modifications of the relative open probability are not. These results strongly suggest that conformational changes of RCK1 domains are specifically coupled to the voltage sensor function during allosteric modulation of BK channels.

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All data generated and analysed during this study are included in the manuscript.

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Pablo Miranda

National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States

For correspondence
pablo.mirandafernandez2@nih.gov

Competing interests
The authors declare that no competing interests exist.
Miguel Holmgren

National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States

Competing interests
The authors declare that no competing interests exist.
Teresa Giraldez

Basic Medical Sciences, Universidad de La Laguna, La Laguna, Spain

For correspondence
giraldez@ull.edu.es

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0002-4096-810X

Funding

National Institutes of Health

Miguel Holmgren

H2020 European Research Council (ERC-CoG-2014-648936)

Teresa Giraldez

Ministerio de Economía y Competitividad (SAF2013-50085-EXP)

Teresa Giraldez

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Copyright

This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.