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Proc Natl Acad Sci U S A. 2011 Oct 25;108(43):17684-9. doi: 10.1073/pnas.1107229108. Epub 2011 Oct 12.

Structure and function of multiple Ca2+-binding sites in a K+ channel regulator of K+ conductance (RCK) domain.

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Department of Biochemistry, Temple University School of Medicine, 3400 North Broad Street, Philadelphia, PA 19140, USA.


Regulator of K(+) conductance (RCK) domains control the activity of a variety of K(+) transporters and channels, including the human large conductance Ca(2+)-activated K(+) channel that is important for blood pressure regulation and control of neuronal firing, and MthK, a prokaryotic Ca(2+)-gated K(+) channel that has yielded structural insight toward mechanisms of RCK domain-controlled channel gating. In MthK, a gating ring of eight RCK domains regulates channel activation by Ca(2+). Here, using electrophysiology and X-ray crystallography, we show that each RCK domain contributes to three different regulatory Ca(2+)-binding sites, two of which are located at the interfaces between adjacent RCK domains. The additional Ca(2+)-binding sites, resulting in a stoichiometry of 24 Ca(2+) ions per channel, is consistent with the steep relation between [Ca(2+)] and MthK channel activity. Comparison of Ca(2+)-bound and unliganded RCK domains suggests a physical mechanism for Ca(2+)-dependent conformational changes that underlie gating in this class of channels.

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