The cavity and pore helices the KcsA K+ channel: Electrostatic stabilization of monovalent cations

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 heli ces is large compared to that described for water-soluble proteins because of the low dielectric membrane environment. The combined contributions of t he ion self-energy and the helix electrostatic field give rise to selectivi ty for monovalent cations in the water-filled cavity. Thus, the K+ channel uses simple electrostatic principles to solve the fundamental problem of io n destabilization by the cell membrane lipid bilayer.