1. Structural Biology and Molecular Biophysics

Structure of the human epithelial sodium channel by cryo-electron microscopy

  1. Sigrid Noreng
  2. Arpita Bharadwaj
  3. Richard Posert
  4. Craig Yoshioka
  5. Isabelle Baconguis  Is a corresponding author
  1. Oregon Health and Science University, United States
  2. Vollum Institute, United States
https://doi.org/10.7554/eLife.39340
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  1. Sigrid Noreng
  2. Arpita Bharadwaj
  3. Richard Posert
  4. Craig Yoshioka
  5. Isabelle Baconguis
(2018)
Structure of the human epithelial sodium channel by cryo-electron microscopy
eLife 7:e39340.
https://doi.org/10.7554/eLife.39340
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Abstract

The epithelial sodium channel (ENaC), a member of the ENaC/DEG superfamily, regulates Na+ and water homeostasis. ENaCs assemble as heterotrimeric channels that harbor protease-sensitive domains critical for gating the channel. Here we present the structure of human ENaC in the uncleaved state determined by single-particle cryo-electron microscopy. The ion channel is composed of a large extracellular domain and a narrow transmembrane domain. The structure reveals that ENaC assembles with a 1:1:1 stoichiometry of α:β:γ subunits arranged in a counter-clockwise manner. The shape of each subunit is reminiscent of a hand with key gating domains of a 'finger' and a 'thumb'. Wedged between these domains is the elusive protease-sensitive inhibitory domain poised to regulate conformational changes of the 'finger' and 'thumb'; thus, the structure provides the first view of the architecture of inhibition of ENaC.

Data availability

The three-dimensional cryo-EM density map and the coordinate for the structure of ΔENAC have been deposited in the EM Database and Protein Data Bank under the accession codes EMD-7130 and 6BQN, respectively.

The following data sets were generated
    1. Noreng S
    2. Bharadwaj A
    3. Posert R
    4. Yoshioka C
    5. Baconguis I
    (2018) ΔENaC model coordinates
    Available at PDB, freely with attribution, provided the user agrees to abide by the conditions described in the PDB Advisory Notice.
    https://www.rcsb.org/structure/6BQN
    1. Noreng S
    2. Bharadwaj A
    3. Posert R
    4. Yoshioka C
    5. Baconguis I
    (2018) ΔENaC map, FSC
    Available at PDB, freely with attribution, provided the user agrees to abide by the conditions described in the PDB Advisory Notice.
    http://emsearch.rutgers.edu/atlas/7130_summary.html

Article and author information

Author details

  1. Sigrid Noreng

    Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, United States
    Competing interests
    The authors declare that no competing interests exist.

  2. Arpita Bharadwaj

    Vollum Institute, Portland, United States
    Competing interests
    The authors declare that no competing interests exist.

  3. Richard Posert

    Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, United States
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-9010-2104

  4. Craig Yoshioka

    Department of Biomedical Engineering, Oregon Health and Science University, Portland, United States
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-0251-7316

  5. Isabelle Baconguis

    Vollum Institute, Portland, United States
    For correspondence
    bacongui@ohsu.edu
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-5440-2289

Funding

National Institutes of Health (DP5OD017871)

  • Isabelle Baconguis

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Sriram Subramaniam, National Cancer Institute, United States

Version history

  1. Received: June 19, 2018
  2. Accepted: September 18, 2018
  3. Accepted Manuscript published: September 25, 2018 (version 1)
  4. Version of Record published: October 22, 2018 (version 2)

Copyright

© 2018, Noreng et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

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  1. Sigrid Noreng
  2. Arpita Bharadwaj
  3. Richard Posert
  4. Craig Yoshioka
  5. Isabelle Baconguis
(2018)
Structure of the human epithelial sodium channel by cryo-electron microscopy
eLife 7:e39340.
https://doi.org/10.7554/eLife.39340

Share this article

https://doi.org/10.7554/eLife.39340

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Further reading

    1. Structural Biology and Molecular Biophysics

    Molecular principles of assembly, activation, and inhibition in epithelial sodium channel

    Sigrid Noreng, Richard Posert ... Isabelle Baconguis
    Research Advance Updated

    The molecular bases of heteromeric assembly and link between Na+ self-inhibition and protease-sensitivity in epithelial sodium channels (ENaCs) are not fully understood. Previously, we demonstrated that ENaC subunits – α, β, and γ – assemble in a counterclockwise configuration when viewed from outside the cell with the protease-sensitive GRIP domains in the periphery (Noreng et al., 2018). Here we describe the structure of ENaC resolved by cryo-electron microscopy at 3 Å. We find that a combination of precise domain arrangement and complementary hydrogen bonding network defines the subunit arrangement. Furthermore, we determined that the α subunit has a primary functional module consisting of the finger and GRIP domains. The module is bifurcated by the α2 helix dividing two distinct regulatory sites: Na+ and the inhibitory peptide. Removal of the inhibitory peptide perturbs the Na+ site via the α2 helix highlighting the critical role of the α2 helix in regulating ENaC function.

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