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Structure and function of multiple Ca 2+ -binding sites in a K + channel regulator of K + conductance (RCK) domain

2011; National Academy of Sciences; Volume: 108; Issue: 43 Linguagem: Inglês

10.1073/pnas.1107229108

1091-6490

Victor P.T. Pau, Frank J. Smith, A.B. Taylor, Liubov Parfenova, Elsie Samakai, Matthew M. Callaghan, Karin Abarca-Heidemann, P. John Hart, Brad S. Rothberg,

Neuroscience and Neuropharmacology Research

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.