Selectivity and Permeation of Alkali Metal Ions in K+-channels

TY - JOUR

T1 - Selectivity and Permeation of Alkali Metal Ions in K+-channels

AU - Furini, Simone

AU - Domene, Carmen

PY - 2011/6/24

Y1 - 2011/6/24

N2 - Ion conduction in K+-channels is usually described in terms of concerted movements of K+ progressing in a single file through a narrow pore. Permeation is driven by an incoming ion knocking on those ions already inside the protein. A fine-tuned balance between high-affinity binding and electrostatic repulsive forces between permeant ions is needed to achieve efficient conduction. While K+-channels are known to be highly selective for K+ over Na+, some K+ channels conduct Na+ in the absence of K+. Other ions are known to permeate K+-channels with a more moderate preference and unusual conduction features. We describe an extensive computational study on ion conduction in K+-channels rendering free energy profiles for the translocation of three different alkali ions and some of their mixtures. The free energy maps for Rb+ translocation show at atomic level why experimental Rb+ conductance is slightly lower than that of K+. In contrast to K+ or Rb+, external Na+ block K+ currents, and the sites where Na+ transport is hindered are characterized. Translocation of K+/Na+ mixtures is energetically unfavorable owing to the absence of equally spaced ion-binding sites for Na+, excluding Na+ from a channel already loaded with K+. (C) 2011 Elsevier Ltd. All rights reserved..

AB - Ion conduction in K+-channels is usually described in terms of concerted movements of K+ progressing in a single file through a narrow pore. Permeation is driven by an incoming ion knocking on those ions already inside the protein. A fine-tuned balance between high-affinity binding and electrostatic repulsive forces between permeant ions is needed to achieve efficient conduction. While K+-channels are known to be highly selective for K+ over Na+, some K+ channels conduct Na+ in the absence of K+. Other ions are known to permeate K+-channels with a more moderate preference and unusual conduction features. We describe an extensive computational study on ion conduction in K+-channels rendering free energy profiles for the translocation of three different alkali ions and some of their mixtures. The free energy maps for Rb+ translocation show at atomic level why experimental Rb+ conductance is slightly lower than that of K+. In contrast to K+ or Rb+, external Na+ block K+ currents, and the sites where Na+ transport is hindered are characterized. Translocation of K+/Na+ mixtures is energetically unfavorable owing to the absence of equally spaced ion-binding sites for Na+, excluding Na+ from a channel already loaded with K+. (C) 2011 Elsevier Ltd. All rights reserved..

KW - molecular dynamics

KW - potassium channels

KW - umbrella sampling

KW - potential of mean force

KW - free energy

KW - POTASSIUM-CHANNEL

KW - MOLECULAR-DYNAMICS

KW - POTENTIAL FUNCTIONS

KW - K+/NA+ SELECTIVITY

KW - BINDING-SITES

KW - KCSA CHANNEL

KW - CONDUCTION

KW - ENERGY

KW - FILTER

KW - WATER

U2 - 10.1016/j.jmb.2011.04.043

DO - 10.1016/j.jmb.2011.04.043

M3 - Article

SN - 0022-2836

VL - 409

SP - 867

EP - 878

JO - Journal of Molecular Biology

JF - Journal of Molecular Biology

IS - 5

ER -