1. Structural Biology and Molecular Biophysics
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Revealing an outward-facing open conformational state in a CLC Cl-/H+ exchange transporter

  1. Chandra M Khantwal
  2. Sherwin J Abraham
  3. Wei Han
  4. Tao Jiang
  5. Tanmay S Chavan
  6. Ricky C Cheng
  7. Shelley M Elvington
  8. Corey W Liu
  9. Irimpan I Mathews
  10. Richard A Stein
  11. Hassane S Mchaourab
  12. Emad Tajkhorshid
  13. Merritt Maduke  Is a corresponding author
  1. Stanford University School of Medicine, United States
  2. University of Illinois at Urbana-Champaign, United States
  3. Stanford University, United States
  4. Vanderbilt University, United States
Research Article
  • Cited 25
  • Views 2,098
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Cite this article as: eLife 2016;5:e11189 doi: 10.7554/eLife.11189

Abstract

CLC secondary active transporters exchange Cl- for H+. Crystal structures have suggested that the conformational change from occluded to outward-facing states is unusually simple, involving only the rotation of a conserved glutamate (Gluex) upon its protonation. Using 19F NMR, we show that as [H+] is increased to protonate Gluex and enrich the outward-facing state, a residue ~20 Å away from Gluex, near the subunit interface, moves from buried to solvent-exposed. Consistent with functional relevance of this motion, constriction via inter-subunit cross-linking reduces transport. Molecular dynamics simulations indicate that the cross-link dampens extracellular gate-opening motions. In support of this model, mutations that decrease steric contact between Helix N (part of the extracellular gate) and Helix P (at the subunit interface) remove the inhibitory effect of the cross-link. Together, these results demonstrate the formation of a previously uncharacterized 'outward-facing open' state, and highlight the relevance of global structural changes in CLC function.

Article and author information

Author details

  1. Chandra M Khantwal

    Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, United States
    Competing interests
    The authors declare that no competing interests exist.
  2. Sherwin J Abraham

    Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, United States
    Competing interests
    The authors declare that no competing interests exist.
  3. Wei Han

    Department of Biochemistry, College of Medicine, Center for Biophysics and Computational Biology, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, United States
    Competing interests
    The authors declare that no competing interests exist.
  4. Tao Jiang

    Department of Biochemistry, College of Medicine, Center for Biophysics and Computational Biology, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, United States
    Competing interests
    The authors declare that no competing interests exist.
  5. Tanmay S Chavan

    Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, United States
    Competing interests
    The authors declare that no competing interests exist.
  6. Ricky C Cheng

    Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, United States
    Competing interests
    The authors declare that no competing interests exist.
  7. Shelley M Elvington

    Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, United States
    Competing interests
    The authors declare that no competing interests exist.
  8. Corey W Liu

    Stanford Magnetic Resonance Laboratory, Stanford University School of Medicine, Stanford, United States
    Competing interests
    The authors declare that no competing interests exist.
  9. Irimpan I Mathews

    Stanford Synchrotron Radiation Lightsource, Stanford University, Menlo Park, United States
    Competing interests
    The authors declare that no competing interests exist.
  10. Richard A Stein

    Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, United States
    Competing interests
    The authors declare that no competing interests exist.
  11. Hassane S Mchaourab

    Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, United States
    Competing interests
    The authors declare that no competing interests exist.
  12. Emad Tajkhorshid

    Department of Biochemistry, College of Medicine, Center for Biophysics and Computational Biology, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, United States
    Competing interests
    The authors declare that no competing interests exist.
  13. Merritt Maduke

    Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, United States
    For correspondence
    maduke@stanford.edu
    Competing interests
    The authors declare that no competing interests exist.

Reviewing Editor

  1. Richard Aldrich, The University of Texas at Austin, United States

Publication history

  1. Received: August 27, 2015
  2. Accepted: January 14, 2016
  3. Accepted Manuscript published: January 22, 2016 (version 1)
  4. Version of Record published: February 18, 2016 (version 2)

Copyright

© 2016, Khantwal 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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