Abstract
Voltage-sensitive potassium ion channels are essential for life, but the molecular basis of their ion conduction is not well understood. In particular, the impact of ion concentration on ion conduction has not been fully studied. We performed several micro-second molecular dynamics simulations of the pore domain of the Kv1.2 potassium channel in KCl solution at four different ion concentrations, and scrutinized each of the conduction events, based on graphical representations of the simulation trajectories. As a result, we observed that the conduction mechanism switched with different ion concentrations: at high ion concentrations, potassium conduction occurred by Hodgkin and Keynes' knock-on mechanism, where the association of an incoming ion with the channel is tightly coupled with the dissociation of an outgoing ion, in a one-step manner. On the other hand, at low ion concentrations, ions mainly permeated by a two-step association/dissociation mechanism, in which the association and dissociation of ions were not coupled, and occurred in two distinct steps. We also found that this switch was triggered by the facilitated association of an ion from the intracellular side within the channel pore and by the delayed dissociation of the outermost ion, as the ion concentration increased.
Highlights
Ion channels play essential roles in establishing accurate communications across plasma membranes
We focused on the ion concentration effects on ion conduction, and presented distinct observations of K+ conductions by the same Kv1.2 channel as in Jensen’s simulation
Conductance We successfully observed repeating ion conduction events in the systems consisting of a homo-tetrameric pore domain of the Kv1.2 channel protein, a POPE membrane, and KCl solution
Summary
Ion channels play essential roles in establishing accurate communications across plasma membranes. We used four different concentrations of KCl: 150 mM, 300 mM, 450 mM, and 600 mM (Fig. 1; the numbers of waters and ions in each system are shown in Table S1), and each simulation time was 1.0 ms, 0.5 ms, 0.5 ms, and 1.0 ms, respectively.
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