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      Instantaneous ion configurations in the K+ ion channel selectivity filter revealed by 2D IR spectroscopy.

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          Abstract

          Potassium channels are responsible for the selective permeation of K(+) ions across cell membranes. K(+) ions permeate in single file through the selectivity filter, a narrow pore lined by backbone carbonyls that compose four K(+) binding sites. Here, we report on the two-dimensional infrared (2D IR) spectra of a semisynthetic KcsA channel with site-specific heavy ((13)C(18)O) isotope labels in the selectivity filter. The ultrafast time resolution of 2D IR spectroscopy provides an instantaneous snapshot of the multi-ion configurations and structural distributions that occur spontaneously in the filter. Two elongated features are resolved, revealing the statistical weighting of two structural conformations. The spectra are reproduced by molecular dynamics simulations of structures with water separating two K(+) ions in the binding sites, ruling out configurations with ions occupying adjacent sites.

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          Author and article information

          Journal
          Science
          Science (New York, N.Y.)
          American Association for the Advancement of Science (AAAS)
          1095-9203
          0036-8075
          September 02 2016
          : 353
          : 6303
          Affiliations
          [1 ] Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA.
          [2 ] Program in Chemical Biology, Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239, USA.
          [3 ] Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA.
          [4 ] Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, IL 60637, USA. eperozo@uchicago.edu roux@uchicago.edu valiyave@ohsu.edu zanni@chem.wisc.edu.
          [5 ] Program in Chemical Biology, Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, OR 97239, USA. eperozo@uchicago.edu roux@uchicago.edu valiyave@ohsu.edu zanni@chem.wisc.edu.
          [6 ] Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA. eperozo@uchicago.edu roux@uchicago.edu valiyave@ohsu.edu zanni@chem.wisc.edu.
          Article
          353/6303/1040 NIHMS884237
          10.1126/science.aag1447
          5544905
          27701114

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