Correlated movements of ions and water in a nanochannel

Abstract

We have studied the molecular mechanism of the ion transport in a long channel ( ≈ 70 Å) filled with an alternating sequence of ions and water molecules at various densities. The molecular structure of the channel was adopted from the structure of the selectivity pore of the KcsA potassium channel. The results from molecular dynamics simulations show that the ion conductivity is based on a fine-tuned interplay between the three constituents of the channel: the ions, the water molecules and the flexible carbonyl groups of the channel's backbone, which represent a one-dimensional fluctuating lattice potential for ions and water. The unidirectional transport is based on the hopping processes of bound ion–water pairs mediated by the lattice potential. The cooperativity of the transport is deduced from the observations that isolated ion–water pairs, and isolated ions in a water-free channel, do not perform long-ranged movements. It is suggested that the water molecules cause a rectification of the movements of ion–water pairs at high densities.

Keywords:

• potassium channel
• permeation
• ion conduction
• molecular dynamics simulation
• incommensurability
• ratchet
• rectification

Notes

^1. Present address: Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan, R.O.C.

Additional information

Notes on contributors

J.F. Gwan

1. 1. Present address: Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan, R.O.C.