Journal of Biological Chemistry
Volume 289, Issue 41, 10 October 2014, Pages 28149-28159
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Membrane Biology
Metal Bridges Illuminate Transmembrane Domain Movements during Gating of the Cystic Fibrosis Transmembrane Conductance Regulator Chloride Channel*

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Opening and closing of the cystic fibrosis transmembrane conductance regulator are controlled by ATP binding and hydrolysis by the cytoplasmic nucleotide-binding domains. Different conformational changes in the channel pore have been described during channel opening and closing; however, the relative importance of these changes to the process of gating the pore is not known. We have used patch clamp recording to identify high affinity Cd2+ bridges formed between pairs of pore-lining cysteine residues introduced into different transmembrane α-helices (TMs). Seven Cd2+ bridges were identified forming between cysteines in TMs 6 and 12. Interestingly, each of these Cd2+ bridges apparently formed only in closed channels, and their formation stabilized the closed state. In contrast, a single Cd2+ bridge identified between cysteines in TMs 1 and 12 stabilized the channel open state. Analysis of the pattern of Cd2+ bridge formation in different channel states suggests that lateral separation and convergence of different TMs, rather than relative rotation or translation of different TMs, is the key conformational change that causes the channel pore to open and close.

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*

This work was supported by the Canadian Institutes of Health Research.

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The abbreviations used are:

    CFTR

    cystic fibrosis transmembrane conductance regulator

    ABC

    ATP-binding cassette

    MSD

    membrane-spanning domain

    NBD

    nucleotide-binding domain

    TM

    transmembrane α-helix.