Potassium and sodium ions in a potassium channel studied by molecular dynamics simulations

We have performed simulations of both a single potassium ion and a single s odium ion within the pore of the bacterial potassium channel KcsA. For both ions then is a dehydration energy barrier at the cytoplasmic mouth suggest ing that the crystal structure is a closed conformation of the channel. The re is a potential energy barrier for a sodium ion in the selectivity filter that is not seen for potassium. Radial distribution functions for both ion s with the carbonyl oxygens of the selectivity filter indicate that sodium may interact more tightly with the tilter than does potassium. This suggest s that the key to the ion selectivity of KcsA is the greater dehydration en ergy of Na+ ions, and helps to explain the block of KcsA by internal Na+ io ns. (C) 2001 Elsevier Science B.V. All rights reserved.