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Mechanism of magnesium activation of calcium-activated potassium channels

Abstract

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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References

  1. Brenner, R. et al. Vasoregulation by the β1 subunit of the calcium-activated potassium channel. Nature 407, 870–876 (2000)

    Article  ADS  CAS  Google Scholar 

  2. Robitaille, R., Garcia, M. L., Kaczorowski, G. J. & Charlton, M. P. Functional colocalization of calcium and calcium-gated potassium channels in control of transmitter release. Neuron 11, 645–655 (1993)

    Article  CAS  Google Scholar 

  3. Isaacson, J. S. & Murphy, G. J. Glutamate-mediated extrasynaptic inhibition: direct coupling of NMDA receptors to Ca(2 + )-activated K+ channels. Neuron 31, 1027–1034 (2001)

    Article  CAS  Google Scholar 

  4. Fettiplace, R. & Fuchs, P. A. Mechanisms of hair cell tuning. Annu. Rev. Physiol. 61, 809–834 (1999)

    Article  CAS  Google Scholar 

  5. Rosenblatt, K. P., Sun, Z. P., Heller, S. & Hudspeth, A. J. Distribution of Ca2+-activated K+ channel isoforms along the tonotopic gradient of the chicken's cochlea. Neuron 19, 1061–1075 (1997)

    Article  CAS  Google Scholar 

  6. Pallotta, B. S., Magleby, K. L. & Barrett, J. N. Single channel recordings of Ca2+-activated K+ currents in rat muscle cell culture. Nature 293, 471–474 (1981)

    Article  ADS  CAS  Google Scholar 

  7. Marty, A. Ca-dependent K channels with large unitary conductance in chromaffin cell membranes. Nature 291, 497–500 (1981)

    Article  ADS  CAS  Google Scholar 

  8. Cui, J., Cox, D. H. & Aldrich, R. W. Intrinsic voltage dependence and Ca2+ regulation of mslo large conductance Ca-activated K+ channels. J. Gen. Physiol. 109, 647–673 (1997)

    Article  CAS  Google Scholar 

  9. Shi, J. & Cui, J. Intracellular Mg(2 + ) enhances the function of BK-type Ca(2 + )-activated K(+ ) channels. J. Gen. Physiol. 118, 589–606 (2001)

    Article  ADS  CAS  Google Scholar 

  10. Zhang, X., Solaro, C. R. & Lingle, C. J. Allosteric regulation of BK channel gating by Ca(2 + ) and Mg(2 + ) through a nonselective, low affinity divalent cation site. J. Gen. Physiol. 118, 607–636 (2001)

    Article  CAS  Google Scholar 

  11. Cui, J. & Aldrich, R. W. Allosteric linkage between voltage and Ca(2 + )-dependent activation of BK-type mslo1 K(+ ) channels. Biochemistry 39, 15612–15619 (2000)

    Article  CAS  Google Scholar 

  12. Jiang, Y., Pico, A., Cadene, M., Chait, B. T. & MacKinnon, R. Structure of the RCK domain from the E. coli K+ channel and demonstration of its presence in the human BK channel. Neuron 29, 593–601 (2001)

    Article  CAS  Google Scholar 

  13. Yellen, G. The moving parts of voltage-gated ion channels. Q. Rev. Biophys. 31, 239–295 (1998)

    Article  CAS  Google Scholar 

  14. Perozo, E., Cortes, D. M. & Cuello, L. G. Structural rearrangements underlying K+-channel activation gating. Science 285, 73–78 (1999)

    Article  CAS  Google Scholar 

  15. Johnson, J. P. Jr & Zagotta, W. N. Rotational movement during cyclic nucleotide-gated channel opening. Nature 412, 917–921 (2001)

    Article  ADS  CAS  Google Scholar 

  16. Butler, A., Tsunoda, S., McCobb, D. P., Wei, A. & Salkoff, L. mSlo, a complex mouse gene encoding ‘maxi’ calcium-activated potassium channels. Science 261, 221–224 (1993)

    Article  ADS  CAS  Google Scholar 

  17. Wei, A., Solaro, C., Lingle, C. & Salkoff, L. Calcium sensitivity of BK-type KCa channels determined by a separable domain. Neuron 13, 671–681 (1994)

    Article  CAS  Google Scholar 

  18. Schreiber, M., Yuan, A. & Salkoff, L. Transplantable sites confer calcium sensitivity to BK channels. Nature Neurosci. 2, 416–421 (1999)

    Article  CAS  Google Scholar 

  19. Bian, S., Favre, I. & Moczydlowski, E. Ca2+-binding activity of a COOH-terminal fragment of the Drosophila BK channel involved in Ca2+-dependent activation. Proc. Natl Acad. Sci. USA 98, 4776–4781 (2001)

    Article  ADS  CAS  Google Scholar 

  20. Schreiber, M. et al. Slo3, a novel pH-sensitive K+ channel from mammalian spermatocytes. J. Biol. Chem. 273, 3509–3516 (1998)

    Article  CAS  Google Scholar 

  21. Adelman, J. P. et al. Calcium-activated potassium channels expressed from cloned complementary DNAs. Neuron 9, 209–216 (1992)

    Article  CAS  Google Scholar 

  22. Milkman, R. An Escherichia coli homologue of eukaryotic potassium channel proteins. Proc. Natl Acad. Sci. USA 91, 3510–3514 (1994)

    Article  ADS  CAS  Google Scholar 

  23. Stock, J. B., Surette, M. G., McCleary, W. R. & Stock, A. M. Signal transduction in bacterial chemotaxis. J. Biol. Chem. 267, 19753–19756 (1992)

    CAS  PubMed  Google Scholar 

  24. Lee, J. O., Rieu, P., Arnaout, M. A. & Liddington, R. Crystal structure of the A domain from the alpha subunit of integrin CR3 (CD11b/CD18). Cell 80, 631–638 (1995)

    Article  CAS  Google Scholar 

  25. Brandeen, C. I. Relation between structure and function of alpha/beta-proteins. Q. Rev. Biophys. 13, 317–338 (1980)

    Article  CAS  Google Scholar 

  26. Needham, J. V., Chen, T. Y. & Falke, J. J. Novel ion specificity of a carboxylate cluster Mg(II) binding site: strong charge selectivity and weak size selectivity. Biochemistry 32, 3363–3367 (1993)

    Article  CAS  Google Scholar 

  27. Flatman, P. W. Mechanisms of magnesium transport. Annu. Rev. Physiol. 53, 259–271 (1991)

    Article  CAS  Google Scholar 

  28. Horovitz, A. & Fersht, A. R. Strategy for analysing the co-operativity of intramolecular interactions in peptides and proteins. J. Mol. Biol. 214, 613–617 (1990)

    Article  CAS  Google Scholar 

  29. Koradi, R., Billeter, M. & Wuthrich, K. MOLMOL: a program for display and analysis of macromolecular structures. J. Mol. Graph. 14, 51–55 (1996)

    Article  CAS  Google Scholar 

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Acknowledgements

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). https://doi.org/10.1038/nature00941

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