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Biophys J, August 2002, p. 633-645, Vol. 83, No. 2

K+ versus Na+ Ions in a K Channel Selectivity Filter: A Simulation Study

Indira H. Shrivastava, D. Peter Tieleman, Philip C. Biggin, and Mark S. P. Sansom

Laboratory of Molecular Biophysics, Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom

Molecular dynamics simulations of a bacterial potassium channel (KcsA) embedded in a phospholipid bilayer reveal significant differences in interactions of the selectivity filter with K+ compared with Na+ ions. K+ ions and water molecules within the filter undergo concerted single-file motion in which they translocate between adjacent sites within the filter on a nanosecond timescale. In contrast, Na+ ions remain bound to sites within the filter and do not exhibit translocation on a nanosecond timescale. Furthermore, entry of a K+ ion into the filter from the extracellular mouth is observed, whereas this does not occur for a Na+ ion. Whereas K+ ions prefer to sit within a cage of eight oxygen atoms of the filter, Na+ ions prefer to interact with a ring of four oxygen atoms plus two water molecules. These differences in interactions in the selectivity filter may contribute to the selectivity of KcsA for K+ ions (in addition to the differences in dehydration energy between K+ and Na+) and the block of KcsA by internal Na+ ions. In our simulations the selectivity filter exhibits significant flexibility in response to changes in ion/protein interactions, with a somewhat greater distortion induced by Na+ than by K+ ions.

Biophys J, August 2002, p. 633-645, Vol. 83, No. 2
© 2002 by the Biophysical Society   0006-3495/02/08/633/13  $2.00


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