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Open structure of the Ca2+ gating ring in the high-conductance Ca2+-activated K+ channel


High-conductance voltage- and Ca2+-activated K+ channels function in many physiological processes that link cell membrane voltage and intracellular Ca2+ concentration, including neuronal electrical activity, skeletal and smooth muscle contraction, and hair cell tuning1,2,3,4,5,6,7,8. Like other voltage-dependent K+ channels, Ca2+-activated K+ channels open when the cell membrane depolarizes, but in contrast to other voltage-dependent K+ channels, they also open when intracellular Ca2+ concentrations rise. Channel opening by Ca2+ is made possible by a structure called the gating ring, which is located in the cytoplasm. Recent structural studies have defined the Ca2+-free, closed, conformation of the gating ring, but the Ca2+-bound, open, conformation is not yet known9. Here we present the Ca2+-bound conformation of the gating ring. This structure shows how one layer of the gating ring, in response to the binding of Ca2+, opens like the petals of a flower. The degree to which it opens explains how Ca2+ binding can open the transmembrane pore. These findings present a molecular basis for Ca2+ activation of K+ channels and suggest new possibilities for targeting the gating ring to treat conditions such as asthma and hypertension.

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Figure 1: The BK channel and the gating ring.
Figure 2: The flexible interface and the assembly interface.
Figure 3: A Ca 2+ -gating model for the BK channel.

Accession codes

Primary accessions

Protein Data Bank

Data deposits

Atomic coordinates and structure factors for the reported crystal structure have been deposited into the Protein Data Bank under accession code 3U6N.


  1. 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 

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

    Article  CAS  Google Scholar 

  3. Nelson, M. T. et al. Relaxation of arterial smooth muscle by calcium sparks. Science 270, 633–637 (1995)

    Article  ADS  CAS  Google Scholar 

  4. 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 

  5. Petkov, G. V. et al. β1-subunit of the Ca2+-activated K+ channel regulates contractile activity of mouse urinary bladder smooth muscle. J. Physiol. (Lond.) 537, 443–452 (2001)

    Article  CAS  Google Scholar 

  6. Lee, U. S. & Cui, J. BK channel activation: structural and functional insights. Trends Neurosci. 33, 415–423 (2010)

    Article  CAS  Google Scholar 

  7. Kaczorowski, G. J., Knaus, H. G., Leonard, R. J., McManus, O. B. & Garcia, M. L. High-conductance calcium-activated potassium channels; structure, pharmacology, and function. J. Bioenerg. Biomembr. 28, 255–267 (1996)

    Article  CAS  Google Scholar 

  8. Salkoff, L., Butler, A., Ferreira, G., Santi, C. & Wei, A. High-conductance potassium channels of the SLO family. Nature Rev. Neurosci. 7, 921–931 (2006)

    Article  CAS  Google Scholar 

  9. Wu, Y., Yang, Y., Ye, S. & Jiang, Y. Structure of the gating ring from the human large-conductance Ca2+-gated K+ channel. Nature 466, 393–397 (2010)

    Article  ADS  CAS  Google Scholar 

  10. 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 

  11. Albright, R. A., Ibar, J. L., Kim, C. U., Gruner, S. M. & Morais-Cabral, J. H. The RCK domain of the KtrAB K+ transporter: multiple conformations of an octameric ring. Cell 126, 1147–1159 (2006)

    Article  CAS  Google Scholar 

  12. Ye, S., Li, Y., Chen, L. & Jiang, Y. Crystal structures of a ligand-free MthK gating ring: insights into the ligand gating mechanism of K+ channels. Cell 126, 1161–1173 (2006)

    Article  CAS  Google Scholar 

  13. Bakker, E. P., Booth, I. R., Dinnbier, U., Epstein, W. & Gajewska, A. Evidence for multiple K+ export systems in Escherichia coli . J. Bacteriol. 169, 3743–3749 (1987)

    Article  CAS  Google Scholar 

  14. Roosild, T. P., Miller, S., Booth, I. R. & Choe, S. A mechanism of regulating transmembrane potassium flux through a ligand-mediated conformational switch. Cell 109, 781–791 (2002)

    Article  CAS  Google Scholar 

  15. Jiang, Y. et al. Crystal structure and mechanism of a calcium-gated potassium channel. Nature 417, 515–522 (2002)

    Article  ADS  CAS  Google Scholar 

  16. Bellamacina, C. R. The nicotinamide dinucleotide binding motif: a comparison of nucleotide binding proteins. FASEB J. 10, 1257–1269 (1996)

    Article  CAS  Google Scholar 

  17. Dong, J., Shi, N., Berke, I., Chen, L. & Jiang, Y. Structures of the MthK RCK domain and the effect of Ca2+ on gating ring stability. J. Biol. Chem. 280, 41716–41724 (2005)

    Article  CAS  Google Scholar 

  18. Yuan, P., Leonetti, M. D., Pico, A. R., Hsiung, Y. & MacKinnon, R. Structure of the human BK channel Ca2+-activation apparatus at 3.0 Å resolution. Science 329, 182–186 (2010)

    Article  ADS  CAS  Google Scholar 

  19. Pico, A. R. RCK Domain Model of Calcium Activation in BK Channels 43–46. PhD thesis, Rockefeller Univ. (2003)

  20. Niu, X., Qian, X. & Magleby, K. L. Linker-gating ring complex as passive spring and Ca2+-dependent machine for a voltage- and Ca2+-activated potassium channel. Neuron 42, 745–756 (2004)

    Article  CAS  Google Scholar 

  21. Zhou, Y., Morais-Cabral, J. H., Kaufman, A. & MacKinnon, R. Chemistry of ion coordination and hydration revealed by a K+ channel–Fab complex at 2.0 Å resolution. Nature 414, 43–48 (2001)

    Article  ADS  CAS  Google Scholar 

  22. Wilkens, C. M. & Aldrich, R. W. State-independent block of BK channels by an intracellular quaternary ammonium. J. Gen. Physiol. 128, 347–364 (2006)

    Article  CAS  Google Scholar 

  23. Li, W. & Aldrich, R. W. State-dependent block of BK channels by synthesized shaker ball peptides. J. Gen. Physiol. 128, 423–441 (2006)

    Article  CAS  Google Scholar 

  24. Zhou, Y., Xia, X. M. & Lingle, C. J. Cysteine scanning and modification reveal major differences between BK channels and Kv channels in the inner pore region. Proc. Natl Acad. Sci. USA 108, 12161–12166 (2011)

    Article  ADS  CAS  Google Scholar 

  25. Tang, Q. Y., Zeng, X. H. & Lingle, C. J. Closed-channel block of BK potassium channels by bbTBA requires partial activation. J. Gen. Physiol. 134, 409–436 (2009)

    Article  CAS  Google Scholar 

  26. Li, W. & Aldrich, R. W. Unique inner pore properties of BK channels revealed by quaternary ammonium block. J. Gen. Physiol. 124, 43–57 (2004)

    Article  CAS  Google Scholar 

  27. Wu, R. S. & Marx, S. O. The BK potassium channel in the vascular smooth muscle and kidney: α- and β-subunits. Kidney Int. 78, 963–974 (2010)

    Article  CAS  Google Scholar 

  28. Ghatta, S., Nimmagadda, D., Xu, X. & O’Rourke, S. T. Large-conductance, calcium-activated potassium channels: structural and functional implications. Pharmacol. Ther. 110, 103–116 (2006)

    Article  CAS  Google Scholar 

  29. Miura, M., Belvisi, M. G., Stretton, C. D., Yacoub, M. H. & Barnes, P. J. Role of potassium channels in bronchodilator responses in human airways. Am. Rev. Respir. Dis. 146, 132–136 (1992)

    Article  CAS  Google Scholar 

  30. Jones, T. R., Charette, L., Garcia, M. L. & Kaczorowski, G. J. Interaction of iberiotoxin with β-adrenoceptor agonists and sodium nitroprusside on guinea pig trachea. J. Appl. Physiol. 74, 1879–1884 (1993)

    Article  CAS  Google Scholar 

  31. Otwinowski, Z. & Minor, W. Processing of X-ray diffraction data collected in oscillation mode. Methods Enzymol. 276, 307–326 (1997)

    Article  CAS  Google Scholar 

  32. Strong, M. et al. Toward the structural genomics of complexes: crystal structure of a PE/PPE protein complex from Mycobacterium tuberculosis . Proc. Natl Acad. Sci. USA 103, 8060–8065 (2006)

    Article  ADS  CAS  Google Scholar 

  33. Potterton, E., Briggs, P., Turkenburg, M. & Dodson, E. A graphical user interface to the CCP4 program suite. Acta Crystallogr. D 59, 1131–1137 (2003)

    Article  Google Scholar 

  34. Emsley, P. & Cowtan, K. Coot: model-building tools for molecular graphics. Acta Crystallogr. D 60, 2126–2132 (2004)

    Article  Google Scholar 

  35. Brunger, A. T. Version 1.2 of the crystallography and NMR system. Nature Protocols 2, 2728–2733 (2007)

    Article  CAS  Google Scholar 

  36. Murshudov, G. N., Vagin, A. A. & Dodson, E. J. Refinement of macromolecular structures by the maximum-likelihood method. Acta Crystallogr. D 53, 240–255 (1997)

    Article  CAS  Google Scholar 

  37. Echols, N., Milburn, D. & Gerstein, M. MolMovDB: analysis and visualization of conformational change and structural flexibility. Nucleic Acids Res. 31, 478–482 (2003)

    Article  CAS  Google Scholar 

  38. Liman, E. R., Tytgat, J. & Hess, P. Subunit stoichiometry of a mammalian K+ channel determined by construction of multimeric cDNAs. Neuron 9, 861–871 (1992)

    Article  CAS  Google Scholar 

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We thank staff members at NSLS X29, Brookhaven National Laboratory, for beamline assistance, and members of the MacKinnon laboratory for discussion. We thank P. Hoff and members of the Gadsby laboratory for help with oocyte preparation. R.M. is an investigator in the Howard Hughes Medical Institute. The research is supported by the American Asthma Foundation grant 07-0127.

Author information

Authors and Affiliations



P.Y. purified and crystallized the protein, collected the X-ray diffraction data, determined the structure and conducted electrophysiology recordings. M.D.L. aided in initial crystallization and electrophysiology experiments. Y.H. provided assistance with protein expression. P.Y. and R.M. designed the research and analysed data. P.Y., M.D.L. and R.M. prepared the manuscript.

Corresponding author

Correspondence to Roderick MacKinnon.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

The file contains Supplementary Table 1 and Supplementary Figures 1-5 with legends. (PDF 3949 kb)

Supplementary Movie 1

This movie shows a morph between the Ca2+-free, closed and Ca2+-bound, open conformations of the BK channel gating ring (RCK1 in blue and RCK2 in red). At 20 seconds, a close-up view at the assembly interface around the Ca2+ bowl is started. At 30 seconds, the pore domain is shown on top of the gating ring. The modeling of the closed and the open conformations of the pore and the gating ring is described in the paper. The N-terminal residues Lys 343 from the RCK1 domains and the last residues from the inner helices are shown as black spheres. The linkers connecting the inner helices to the gating ring are illustrated as dashed lines colored in black. (MPG 16218 kb)

Supplementary Movie 2

This movie shows a morph between the closed (PDB 2FY8) and the open (PDB 1LNQ) conformations of the MthK channel gating ring. (MPG 3686 kb)

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Yuan, P., Leonetti, M., Hsiung, Y. et al. Open structure of the Ca2+ gating ring in the high-conductance Ca2+-activated K+ channel. Nature 481, 94–97 (2012).

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