The cavity and pore helices in 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 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.
Roux
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B
GRTM, Dipartements de Physique et Chimie, Université de Montréal, Case Postal 6128, succursale Centre-Ville, Montréal, Canada H3C 3J7.
MacKinnon
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R
D001426:Bacterial Proteins; D002414:Cations, Monovalent / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D017136:Ion Transport; D008051:Lipid Bilayers; D008958:Models, Molecular; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D055672:Static Electricity; D013302:Streptomyces / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water
D001426:Bacterial Proteins; D002414:Cations, Monovalent; D008051:Lipid Bilayers; D015221:Potassium Channels; C107790:prokaryotic potassium channel; D014867:Water; D011188:Potassium