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Mechanism of magnesium activation of calcium-activated potassium channels


Large-conductance (BK type) Ca2+-dependent K+ channels are essential for modulating muscle contraction and neuronal activities such as synaptic transmission and hearing1,2,3,4,5. BK channels are activated by membrane depolarization and intracellular Ca2+ and Mg2+ (refs 6–10). The energy provided by voltage, Ca2+ and Mg2+ binding are additive in activating the channel, suggesting that these signals open the activation gate through independent pathways9,11. Here we report a molecular investigation of a Mg2+-dependent activation mechanism. Using a combined site-directed mutagenesis and structural analysis, we demonstrate that a structurally new Mg2+-binding site in the RCK/Rossman fold domain—an intracellular structural motif that immediately follows the activation gate S6 helix12,13,14,15—is responsible for Mg2+-dependent activation. Mutations that impair or abolish Mg2+ sensitivity do not affect Ca2+ sensitivity, and vice versa. These results indicate distinct structural pathways for Mg2+- and Ca2+-dependent activation and suggest a possible mechanism for the coupling between Mg2+ binding and channel opening.

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Figure 1: Results of chimaeric channels.
Figure 2: Results of site-directed mutations.
Figure 3: Structure of the Mg2+-binding site.
Figure 4: Results of site-directed mutations that affect channel gating.


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The mSlo1 and mSlo3 clones were provided by L. Salkoff. We thank S. Chen, S. W. Jones and R. Aldrich for comments on the manuscript. This work was supported by grants from the NIH (to J.Q. and J.C.), the American Heart Association and the Whitaker Foundation (to J.C.).

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Correspondence to Jianmin Cui.

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Shi, J., Krishnamoorthy, G., Yang, Y. et al. Mechanism of magnesium activation of calcium-activated potassium channels. Nature 418, 876–880 (2002).

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