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Structure of the gating ring from the human large-conductance Ca2+-gated K+ channel


Large-conductance Ca2+-gated K+ (BK) channels are essential for many biological processes such as smooth muscle contraction and neurotransmitter release1,2,3,4. This group of channels can be activated synergistically by both voltage and intracellular Ca2+, with the large carboxy-terminal intracellular portion being responsible for Ca2+ sensing5,6,7,8,9,10,11,12,13. Here we present the crystal structure of the entire cytoplasmic region of the human BK channel in a Ca2+-free state. The structure reveals four intracellular subunits, each comprising two tandem RCK domains, assembled into a gating ring similar to that seen in the MthK channel14 and probably representing its physiological assembly. Three Ca2+ binding sites including the Ca2+ bowl are mapped onto the structure based on mutagenesis data. The Ca2+ bowl, located within the second RCK domain, forms an EF-hand-like motif and is strategically positioned close to the assembly interface between two subunits. The other two Ca2+ (or Mg2+) binding sites, Asp 367 and Glu 374/Glu 399, are located on the first RCK domain. The Asp 367 site has high Ca2+ sensitivity and is positioned in the groove between the amino- and carboxy-terminal subdomains of RCK1, whereas the low-affinity Mg2+-binding Glu 374/Glu 399 site is positioned on the upper plateau of the gating ring and close to the membrane. Our structure also contains the linker connecting the transmembrane and intracellular domains, allowing us to dock a voltage-gated K+ channel pore of known structure onto the gating ring with reasonable accuracy and generate a structural model for the full BK channel.

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Figure 1: The BK intracellular subunit contains two RCK domains.
Figure 2: Four BK intracellular subunits assemble into a gating ring.
Figure 3: Ca 2+ binding sites in the BK intracellular subunit.
Figure 4: Structure of the linker between the gating ring and the channel pore.

Accession codes

Primary accessions

Protein Data Bank

Data deposits

The atomic coordinates and structure factors have been deposited in the Protein Data Bank under accession number 3NAF.


  1. 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)

    CAS  Article  Google Scholar 

  2. Latorre, R., Oberhauser, A., Labarca, P. & Alvarez, O. Varieties of calcium-activated potassium channels. Annu. Rev. Physiol. 51, 385–399 (1989)

    CAS  Article  Google Scholar 

  3. Cui, J., Yang, H. & Lee, U. S. Molecular mechanisms of BK channel activation. Cell. Mol. Life Sci. 66, 852–875 (2008)

    Article  Google Scholar 

  4. Magleby, K. L. Gating mechanism of BK (Slo1) channels: so near, yet so far. J. Gen. Physiol. 121, 81–96 (2003)

    CAS  Article  Google Scholar 

  5. 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)

    CAS  Article  Google Scholar 

  6. Schreiber, M. & Salkoff, L. A novel calcium-sensing domain in the BK channel. Biophys. J. 73, 1355–1363 (1997)

    CAS  Article  Google Scholar 

  7. Bao, L., Kaldany, C., Holmstrand, E. C. & Cox, D. H. Mapping the BKCa channel’s “Ca2+ bowl”: side-chains essential for Ca2+ sensing. J. Gen. Physiol. 123, 475–489 (2004)

    CAS  Article  Google Scholar 

  8. Zhang, X., Solaro, C. R. & Lingle, C. J. Allosteric regulation of BK channel gating by Ca2+ and Mg2+ through a nonselective, low affinity divalent cation site. J. Gen. Physiol. 118, 607–636 (2001)

    CAS  Article  Google Scholar 

  9. Bao, L., Rapin, A. M., Holmstrand, E. C. & Cox, D. H. Elimination of the BKCa channel’s high-affinity Ca2+ sensitivity. J. Gen. Physiol. 120, 173–189 (2002)

    CAS  Article  Google Scholar 

  10. Xia, X. M., Zeng, X. & Lingle, C. J. Multiple regulatory sites in large-conductance calcium-activated potassium channels. Nature 418, 880–884 (2002)

    CAS  ADS  Article  Google Scholar 

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

    CAS  ADS  Article  Google Scholar 

  12. Zeng, X. H., Xia, X. M. & Lingle, C. J. Divalent cation sensitivity of BK channel activation supports the existence of three distinct binding sites. J. Gen. Physiol. 125, 273–286 (2005)

    CAS  Article  Google Scholar 

  13. Xia, X. M., Zhang, X. & Lingle, C. J. Ligand-dependent activation of Slo family channels is defined by interchangeable cytosolic domains. J. Neurosci. 24, 5585–5591 (2004)

    CAS  Article  Google Scholar 

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

    CAS  ADS  Article  Google Scholar 

  15. Hou, S., Heinemann, S. H. & Hoshi, T. Modulation of BKCa channel gating by endogenous signaling molecules. Physiology 24, 26–35 (2009)

    CAS  Article  Google Scholar 

  16. 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)

    CAS  Article  Google Scholar 

  17. 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)

    CAS  Article  Google Scholar 

  18. 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)

    CAS  Article  Google Scholar 

  19. Kim, H. J., Lim, H. H., Rho, S. H., Eom, S. H. & Park, C. S. Hydrophobic interface between two regulators of K+ conductance domains critical for calcium-dependent activation of large conductance Ca2+-activated K+ channels. J. Biol. Chem. 281, 38573–38581 (2006)

    CAS  Article  Google Scholar 

  20. Yusifov, T., Savalli, N., Gandhi, C. S., Ottolia, M. & Olcese, R. The RCK2 domain of the human BKCa channel is a calcium sensor. Proc. Natl Acad. Sci. USA 105, 376–381 (2008)

    CAS  ADS  Article  Google Scholar 

  21. Wang, L. & Sigworth, F. J. Structure of the BK potassium channel in a lipid membrane from electron cryomicroscopy. Nature 461, 292–295 (2009)

    CAS  ADS  Article  Google Scholar 

  22. Horrigan, F. T. & Aldrich, R. W. Coupling between voltage sensor activation, Ca2+ binding and channel opening in large conductance (BK) potassium channels. J. Gen. Physiol. 120, 267–305 (2002)

    CAS  Article  Google Scholar 

  23. Lingle, C. J. Setting the stage for molecular dissection of the regulatory components of BK channels. J. Gen. Physiol. 120, 261–265 (2002)

    CAS  Article  Google Scholar 

  24. Falke, J. J., Drake, S. K., Hazard, A. L. & Peersen, O. B. Molecular tuning of ion binding to calcium signaling proteins. Q. Rev. Biophys. 27, 219–290 (1994)

    CAS  Article  Google Scholar 

  25. Gifford, J. L., Walsh, M. P. & Vogel, H. J. Structures and metal-ion-binding properties of the Ca2+-binding helix-loop-helix EF-hand motifs. Biochem. J. 405, 199–221 (2007)

    CAS  Article  Google Scholar 

  26. Hou, S., Xu, R., Heinemann, S. H. & Hoshi, T. Reciprocal regulation of the Ca2+ and H+ sensitivity in the SLO1 BK channel conferred by the RCK1 domain. Nature Struct. Mol. Biol. 15, 403–410 (2008)

    CAS  Article  Google Scholar 

  27. Yang, H. et al. Activation of Slo1 BK channels by Mg2+ coordinated between the voltage sensor and RCK1 domains. Nature Struct. Mol. Biol. 15, 1152–1159 (2008)

    CAS  Article  Google Scholar 

  28. 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)

    CAS  Article  Google Scholar 

  29. Long, S. B., Tao, X., Campbell, E. B. & MacKinnon, R. Atomic structure of a voltage-dependent K+ channel in a lipid membrane-like environment. Nature 450, 376–382 (2007)

    CAS  ADS  Article  Google Scholar 

  30. 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 10.1126/science.1190414 (27 May 2010)

  31. Zerangue, N., Jan, Y. N. & Jan, L. Y. An artificial tetramerization domain restores efficient assembly of functional Shaker channels lacking T1. Proc. Natl Acad. Sci. USA 97, 3591–3595 (2000)

    CAS  ADS  Article  Google Scholar 

  32. Harbury, P. B., Zhang, T., Kim, P. S. & Alber, T. A switch between two-, three-, and four-stranded coiled coils in GCN4 leucine zipper mutants. Science 262, 1401–1407 (1993)

    CAS  ADS  Article  Google Scholar 

  33. Cronin, C. N., Lim, K. B. & Rogers, J. Production of selenomethionyl-derivatized proteins in baculovirus-infected insect cells. Protein Sci. 16, 2023–2029 (2007)

    CAS  Article  Google Scholar 

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

    CAS  Article  Google Scholar 

  35. Schneider, T. R. & Sheldrick, G. M. Substructure solution with SHELXD. Acta Crystallogr. D 58, 1772–1779 (2002)

    Article  Google Scholar 

  36. Vonrhein, C., Blanc, E., Roversi, P. & Bricogne, G. Automated structure solution with autoSHARP. Methods Mol. Biol. 364, 215–230 (2007)

    CAS  Google Scholar 

  37. Collaborative Computational Project, Number 4. The CCP4 suite: programs for protein crystallography. Acta Crystallogr. D 50, 760–763 (1994)

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

    Article  Google Scholar 

  39. Adams, P. D. et al. PHENIX: a comprehensive Python-based system for macromolecular structure solution. Acta Crystallogr. D 66, 213–221 (2010)

    CAS  Article  Google Scholar 

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We thank A. Alam and M. Derebe for manuscript preparation; A. Pico for discussion in the early stages of this study; and X. Zhang for help in structure determination. Use of the Advanced Photon Source (APS) was supported by the US Department of Energy, Office of Energy Research. We thank the beamline (23ID and 19ID) staff for assistance in data collection. This work was supported by Howard Hughes Medical Institute and by grants from the NIH/NIGMS (RO1 GM071621) and Welch Foundation.

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Y.W. performed sample preparation and structure determination. Y.Y. performed protein expression and purification. S.Y. performed model building and refinement. Y.W. and Y.J. designed the research, analysed data and prepared the manuscript.

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Correspondence to Youxing Jiang.

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The authors declare no competing financial interests.

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

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