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Potassium channels enable K(+) ions to move passively across biological membranes. Multiple nanosecond-duration molecular dynamics simulations (total simulation time 5 ns) of a bacterial potassium channel (KcsA) embedded in a phospholipid bilayer reveal motions of ions, water, and protein. Comparison of simulations with and without K(+) ions indicate that the absence of ions destabilizes the structure of the selectivity filter. Within the selectivity filter, K(+) ions interact with the backbone (carbonyl) oxygens, and with the side-chain oxygen of T75. Concerted single-file motions of water molecules and K(+) ions within the selectivity filter of the channel occur on a 100-ps time scale. In a simulation with three K(+) ions (initially two in the filter and one in the cavity), the ion within the central cavity leaves the channel via its intracellular mouth after approximately 900 ps; within the cavity this ion interacts with the Ogamma atoms of two T107 side chains, revealing a favorable site within the otherwise hydrophobically lined cavity. Exit of this ion from the channel is enabled by a transient increase in the diameter of the intracellular mouth. Such "breathing" motions may form the molecular basis of channel gating.

Original publication

DOI

10.1016/S0006-3495(00)76616-1

Type

Journal article

Journal

Biophys J

Publication Date

02/2000

Volume

78

Pages

557 - 570

Keywords

Bacterial Proteins, Cell Membrane Permeability, Computer Simulation, Kinetics, Lipid Bilayers, Membrane Lipids, Phospholipids, Potassium, Potassium Channels, Protein Structure, Secondary, Proteolipids, Streptomyces, Water