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Structure of the carboxy-terminal region of a KCNH channel

Nature volume 481, pages 530–533 (2012)Cite this article

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Abstract

The KCNH family of ion channels, comprising ether-à-go-go (EAG), EAG-related gene (ERG), and EAG-like (ELK) K+-channel subfamilies, is crucial for repolarization of the cardiac action potential1, regulation of neuronal excitability2 and proliferation of tumour cells3. The carboxy-terminal region of KCNH channels contains a cyclic-nucleotide-binding homology domain (CNBHD) and C-linker that couples the CNBHD to the pore4. The C-linker/CNBHD is essential for proper function and trafficking of ion channels in the KCNH family5,6,7,8,9. However, despite the importance of the C-linker/CNBHD for the function of KCNH channels, the structural basis of ion-channel regulation by the C-linker/CNBHD is unknown. Here we report the crystal structure of the C-linker/CNBHD of zebrafish ELK channels at 2.2-Å resolution. Although the overall structure of the C-linker/CNBHD of ELK channels is similar to the cyclic-nucleotide-binding domain (CNBD) structure of the related hyperpolarization-activated cyclic-nucleotide-modulated (HCN) channels10, there are marked differences. Unlike the CNBD of HCN, the CNBHD of ELK displays a negatively charged electrostatic profile that explains the lack of binding and regulation of KCNH channels by cyclic nucleotides4,11. Instead of cyclic nucleotide, the binding pocket is occupied by a short β-strand. Mutations of the β-strand shift the voltage dependence of activation to more depolarized voltages, implicating the β-strand as an intrinsic ligand for the CNBHD of ELK channels. In both ELK and HCN channels the C-linker is the site of virtually all of the intersubunit interactions in the C-terminal region. However, in the zebrafish ELK structure there is a reorientation in the C-linker so that the subunits form dimers instead of tetramers, as observed in HCN channels. These results provide a structural framework for understanding the regulation of ion channels in the KCNH family by the C-linker/CNBHD and may guide the design of specific drugs.

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Figure 1: Topology and electrophysiological properties of zebrafish ELK channels.
Figure 2: Structure of the C-linker/CNBHD.
Figure 3: Structural comparison of the C-linker regions and quaternary arrangement of the C-linker/CNBHDs of zebrafish ELK and HCN2 channels.

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Accession codes

Primary accessions

Protein Data Bank

Data deposits

Atomic coordinates and structure factors for the reported crystal structures have been deposited with the Protein Data Bank under accession codes 3UKN, 3UKT and 3UKV (see Supplementary Table 1 for identifications).

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Acknowledgements

We thank M. Munari, S. Camp, S. Cunnington and G. Sheridan for excellent technical assistance. We thank the beamline staff at the Advanced Light Source (ALS) and especially P. Zwart for help with data analysis. We also thank the members of the Zagotta laboratory for helpful discussions. This work was supported by the Howard Hughes Medical Institute, National Institutes of Health (NIH) grant R01 EY010329 (W.N.Z.) and NIH grant F32 HL095241 (A.E.C.). The Berkeley Center for Structural Biology is supported in part by the NIH, National Institute of General Medical Sciences and the Howard Hughes Medical Institute. The ALS is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231.

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Authors and Affiliations

  1. Department of Physiology and Biophysics, University of Washington School of Medicine, Box 357290, Seattle, Washington 98195-7290, USA,

    Tinatin I. Brelidze, Anne E. Carlson & William N. Zagotta

  2. Berkeley Center for Structural Biology, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, BLDG 6R2100, Berkeley, California 94720, USA ,

    Banumathi Sankaran

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  1. Tinatin I. Brelidze
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Contributions

T.I.B. and W.N.Z. conceived the experiments. T.I.B. performed the crystallographic experiments, and B.S. helped with the crystallographic data analysis. A.E.C. and W.N.Z. performed the electrophysiology experiments and data analysis. T.I.B. and W.N.Z. wrote the manuscript.

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Correspondence to William N. Zagotta.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Figures 1-10 with legends, Supplementary Table 1, a Supplementary Discussion and additional references. This file was replaced on 18 April 2012 (PDF 6933 kb)

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Brelidze, T., Carlson, A., Sankaran, B. et al. Structure of the carboxy-terminal region of a KCNH channel. Nature 481, 530–533 (2012). https://doi.org/10.1038/nature10735

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