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Structure of a CLC chloride ion channel by cryo-electron microscopy

Nature volume 541, pages 500505 (26 January 2017) | Download Citation

Abstract

CLC proteins transport chloride (Cl) ions across cellular membranes to regulate muscle excitability, electrolyte movement across epithelia, and acidification of intracellular organelles. Some CLC proteins are channels that conduct Cl ions passively, whereas others are secondary active transporters that exchange two Cl ions for one H+. The structural basis underlying these distinctive transport mechanisms is puzzling because CLC channels and transporters are expected to share the same architecture on the basis of sequence homology. Here we determined the structure of a bovine CLC channel (CLC-K) using cryo-electron microscopy. A conserved loop in the Cl transport pathway shows a structure markedly different from that of CLC transporters. Consequently, the cytosolic constriction for Cl passage is widened in CLC-K such that the kinetic barrier previously postulated for Cl/H+ transporter function would be reduced. Thus, reduction of a kinetic barrier in CLC channels enables fast flow of Cl down its electrochemical gradient.

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Acknowledgements

We thank M. Ebrahim at the Rockefeller University Cryo-EM Resource Center for help with microscope operation, staff at the Memorial Sloan Kettering Cancer Center Antibody & Bioresource Core Facility for hybridoma generation, Y. C. Hsiung for help with large-scale cell culture, members of the MacKinnon laboratory for helpful discussions, and J. Chen for critical reading of the manuscript. E.P. is supported by the Jane Coffin Childs Memorial Fund fellowship (#61-1513). R.M. is a Howard Hughes Medical Institute investigator.

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  1. Laboratory of Molecular Neurobiology and Biophysics and Howard Hughes Medical Institute, The Rockefeller University, 1230 York Avenue, New York, New York 10065, USA

    • Eunyong Park
    • , Ernest B. Campbell
    •  & Roderick MacKinnon

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Contributions

E.P. performed experiments. E.B.C. assisted in development of monoclonal antibodies. E.P. and R.M. designed experiments, analysed and interpreted results, and wrote the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Roderick MacKinnon.

Reviewer Information Nature thanks C. Miller, M. Pusch, S. Scheres and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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https://doi.org/10.1038/nature20812

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