We show that in the potassium channel KcsA, proton-dependent activation is followed by an inactivation process similar to C-type inactivation, and this process is suppressed by an E71A mutation in the pore helix. EPR spectroscopy demonstrates that the inner gate opens maximally at low pH regardless of the magnitude of the single-channel-open probability, implying that stationary gating originates mostly from rearrangements at the selectivity filter. Two E71A crystal structures obtained at 2.5 Å reveal large structural excursions of the selectivity filter during ion conduction and provide a glimpse of the range of conformations available to this region of the channel during gating. These data establish a mechanistic basis for the role of the selectivity filter during channel activation and inactivation.
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We thank J. Bushweller, R. Nakamoto and S. Chakrapani for critically reading the manuscript; the staff at BNL X-4A and X-29 for assistance in data collection; R. MacKinnon (Rockefeller University) for providing the KcsA monoclonal antibody hybridoma cell line and F.W. Garcia for assistance with monoclonal antibodies; and H. Wu for generous access to her laboratory space and facilities. V. Vasquez provided assistance with mutagenesis and channel biochemistry; C. Gonzalez provided comments and experimental advice. This work was supported by grants from the US National Institutes of Health to E.P. and B.R.
The authors declare no competing financial interests.
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Cordero-Morales, J., Cuello, L., Zhao, Y. et al. Molecular determinants of gating at the potassium-channel selectivity filter. Nat Struct Mol Biol 13, 311–318 (2006). https://doi.org/10.1038/nsmb1069
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