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The cavity and pore helices in the KcsA K+ channel: electrostatic stabilization of monovalent cations
1GRTM, Dipartements de Physique et Chimie, Université de Montréal, Case Postal 6128, succursale Centre-Ville, Montréal, Canada H3C 3J7.
Abstract:
The electrostatic influence of the central cavity and pore alpha helices in the potassium ion channel from Streptomyces lividans (KcsA K+ channel) was analyzed by solving the finite difference Poisson equation. The cavity and helices overcome the destabilizing influence of the membrane and stabilize a cation at the membrane center. The electrostatic effect of the pore helices is large compared to that described for water-soluble proteins because of the low dielectric membrane environment. The combined contributions of the ion self-energy and the helix electrostatic field give rise to selectivity for monovalent cations in the water-filled cavity. Thus, the K+ channel uses simple electrostatic principles to solve the fundamental problem of ion destabilization by the cell membrane lipid bilayer.
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