Chemistry of ion coordination and hydration revealed by a K+ channel–Fab complex at 2.0 Å resolution

Yufeng Zhou, João H. Morais-Cabral, Amelia Kaufman and Roderick MacKinnon ()
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Yufeng Zhou: Howard Hughes Medical Institute, Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University
João H. Morais-Cabral: Howard Hughes Medical Institute, Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University
Amelia Kaufman: Howard Hughes Medical Institute, Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University
Roderick MacKinnon: Howard Hughes Medical Institute, Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University

Nature, 2001, vol. 414, issue 6859, 43-48

Abstract: Abstract Ion transport proteins must remove an ion's hydration shell to coordinate the ion selectively on the basis of its size and charge. To discover how the K+ channel solves this fundamental aspect of ion conduction, we solved the structure of the KcsA K+ channel in complex with a monoclonal Fab antibody fragment at 2.0 Å resolution. Here we show how the K+ channel displaces water molecules around an ion at its extracellular entryway, and how it holds a K+ ion in a square antiprism of water molecules in a cavity near its intracellular entryway. Carbonyl oxygen atoms within the selectivity filter form a very similar square antiprism around each K+ binding site, as if to mimic the waters of hydration. The selectivity filter changes its ion coordination structure in low K+ solutions. This structural change is crucial to the operation of the selectivity filter in the cellular context, where the K+ ion concentration near the selectivity filter varies in response to channel gating.

Date: 2001
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DOI: 10.1038/35102009

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