Potassium channels
are responsible for the selective
yet efficient
permeation of potassium ions across cell membranes. Despite many available
high-resolution structures of potassium channels, those conformations
inform only on static information on the ion permeation processes.
Here, we use molecular dynamics simulations and Markov state models
to obtain dynamical details of ion permeation. The permeation cycles,
expressed in terms of selectivity filter occupancy and representing
ion permeation events, are illustrated. We show that the direct knock-on
permeation represents the dominant permeation mechanism over a wide
range of potassium concentrations, temperatures, and membrane voltages
for the pore of MthK. Direct knock-on is also observed in other potassium
channels with a highly conserved selectivity filter, demonstrating
the robustness of the permeation mechanism. Lastly, we investigate
the charge strength dependence of permeation cycles. Our results shed
light on the underlying permeation details, which are valuable in
studying conduction mechanisms in potassium channels.