National Center for Design of
Biomimetic Nanoconductors

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K+ ion coordination in selectivity filters of K-channels

K+ ion coordination in selectivity filters of K-channels is markedly different from that in bulk water. KcsA, for example, offers three binding sites for K+ ions (2), S1–S3, where it coordinates with the ion using eight of its backbone carbonyl oxygen atoms (highlighted in red) at an average distance of 2.8 A˚ . In contrast, in a 40-ps-long AIMD (PW91) simulation of K+ ion in bulk water (generated by extending the previously reported (8) 14- ps-long trajectory), only four water molecules are seen most tightly bound to the K+ ion at an average distance of 2.8 A˚ . These four water molecules correspond to the maximum number that contribute to the principle maxima of the radial distribution function (g(r)); the fifth and the sixth nearest waters statistically do not contribute to the peak of the principal maxima; whereas the seventh and the eighth nearest waters are seldom seen within the canonical inner coordination shell (gray area) of the ion. From S. Varma & S. B. Rempe, Tuning Ion Coordination Architectures to Enable Selective Partitioning, Biophys J., 93, 1093-1099, 2007.

The National Center for Design of Biomimetic Nanoconductors is funded by Grant Number PHS 2 PN2 EY016570B from the National Institutes of Health through the NIH Roadmap for Medical Research and is based at the Beckman Institute for Advanced Science and Technology at the University of Illinois at Urbana-Champaign. Partner institutions include University of Chicago, Illinois Institute of Technology, Sandia National Laboratories, Wabash College, University of California, Davis, and the University of New Mexico, University of Illinois at Chicago, Weill Cornell Medical College, and the National Institute of Standards and Technology.