A CLC-ec1 mutant reveals global conformational change and suggests a unifying mechanism for the Cl–/H+ transport cycle
Abstract
Among coupled exchangers, CLCs uniquely catalyze the exchange of oppositely charged ions (Cl– for H+). Transport-cycle models to describe and explain this unusual mechanism have been proposed based on known CLC structures. While the proposed models harmonize with many experimental findings, gaps and inconsistencies in our understanding have remained. One limitation has been that global conformational change – which occurs in all conventional transporter mechanisms – has not been observed in any high-resolution structure. Here, we describe the 2.6 Å structure of a CLC mutant designed to mimic the fully H+-loaded transporter. This structure reveals a global conformational change to improve accessibility for the Cl– substrate from the extracellular side and new conformations for two key glutamate residues. Together with DEER measurements, MD simulations, and functional studies, this new structure `provides evidence for a unified model of H+ /Cl– transport that reconciles existing data on all CLC-type proteins.
Data availability
Diffraction data have been deposited in PDB under accession code 6V2J
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Crystal structure of ClC-ec1 triple mutant (E113Q, E148Q, E203Q)Protein Data Bank, 6V2J.
Article and author information
Author details
Funding
National Institutes of Health (GM113195)
- Hassane S Mchaourab
- Emad Tajkhorshid
- Merritt Maduke
American Heart Association (17POST33670553)
- Tanmay S Chavan
U.S. Department of Energy (DE-AC02-06CH11357)
- Antoine Koehl
National Institutes of Health (P41GM103393)
- Irimpan I Mathews
Blue Waters at National Center for Supercomputing Applications
- Tao Jiang
Extreme Science and Engineering Discovery Environment (MCA06N060)
- Emad Tajkhorshid
National Institutes of Health (P41-GM104601)
- Emad Tajkhorshid
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Reviewing Editor
- Leon D Islas, Universidad Nacional Autónoma de México, Mexico
Version history
- Received: November 9, 2019
- Accepted: April 18, 2020
- Accepted Manuscript published: April 20, 2020 (version 1)
- Version of Record published: May 27, 2020 (version 2)
Copyright
© 2020, Chavan 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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