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

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Abstract

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.

Data availability

All cryo-EM maps have been deposited in the Electron Microscopy Data Bank under the accession code EMD-21896 for ENaC. Model coordinates have been deposited in the Protein Data Bank under the accession code 6WTH.

The following data sets were generated

1. Baconguis I
2. et al
(2020) cryo-EM maps for ENac
EMD-21896.

http://www.ebi.ac.uk/pdbe/entry/emdb/EMD-21896
1. Baconguis I
2. et al
(2020) Model coordinates
Protein Data Bank, 6WTH.

http://www.rcsb.org/structure/6WTH

Article and author information

Author details

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.

"This ORCID iD identifies the author of this article:" 0000-0001-5767-1399
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.

"This ORCID iD identifies the author of this article:" 0000-0001-9010-2104
Arpita Bharadwaj

Vollum Institute, Oregon Health and Science University, Portland, United States

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0002-3867-7610
Alexandra Houser

Neuroscience Graduate Program, Oregon Health and Science University, Portland, United States

Competing interests
The authors declare that no competing interests exist.
Isabelle Baconguis

Vollum Institute, Oregon Health and Science University, Portland, United States

For correspondence
bacongui@ohsu.edu

Competing interests
The authors declare that no competing interests exist.

"This ORCID iD identifies the author of this article:" 0000-0002-5440-2289

Funding

National Institutes of Health (DP5OD017871)

Isabelle Baconguis

American Heart Association (19TPA34760754)

Isabelle Baconguis

American Heart Association (18PRE33990205)

Sigrid Noreng

National Science Foundation (DGE-1937961)

Alexandra Houser

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

Copyright

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.