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

Abstract

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.

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Acknowledgements

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). https://doi.org/10.1038/nature09252

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