Water and potassium dynamics inside the KcsA K+ channel

Molecular dynamics simulations and electrostatic modeling are used to inves tigate structural and dynamical properties of the potassium ions and of wat er molecules inside the KcsA channel immersed in a membrane-mimetic environ ment. Two potassium ions, initially located in the selectivity filter bindi ng sites, maintain their position during 2 ns of dynamics. A third potassiu m ion is very mobile in the water-filled cavity, The protein appears engine ered so as to polarize water molecules inside the channel cavity. The resul ting water induced dipole and the positively charged potassium ion within t he cavity are the key ingredients for stabilizing the two K+ ions in the bi nding sites. These two ions experience single file movements upon removal o f the potassium in the cavity, confirming the role of the latter in ion tra nsport through the channel. (C) 2000 Federation of European Biochemical Soc ieties. Published by Elsevier Science B.V. All rights reserved.