Microscopic Mechanism of Ion Permeation through K+ Channel

Abstract

One of the most basic roles of ion channel is the passive transport of ions through the hydrophilic pore enabling the dehydration of ions. Since the determination of the x-ray crystallographic structure of the K+ channel, many theoretical studies on the ion permeation have been performed. However, the microscopic mechanism of ion permeation, the essence of ion channel, has not been clarified yet.We study the passive transport of ions through the K+ channel, Kv1.2, by the molecular dynamics simulation in which the electric field is applied. A number of ion permeation is successfully observed. The number of permeated ion, i.e., the channel conductance is mostly proportional to the ion concentration of the bulk. The number of ions in the central cavity also depends on the ion concentration. Although the ions and water molecules are transported alternately, surprisingly, the other manner of ion permeation is also observed. That is, ions can permeate without intervening water molecule at high concentration, on the other hand, a permeating ion is accompanied by two water molecules at low concentration. Therefore, the microscopic mechanism of ion permeation depends on the ion concentration, and the physiological fact that an ion permeates per a water molecule is considered to be the average of these two cases. We also discuss the role of the central cavity by comparing the ion permeation in the channel with that in the model channel.