INVESTIGATING THE DIELECTRIC EFFECTS OF CHANNEL PORE-WATER ON THE ELECTROSTATIC BARRIERS OF THE PERMEATION ION BY THE FINITE-DIFFERENCE POISSON-BOLTZMANN METHOD

In this paper, the finite difference Poisson-Boltzmann (FDPB) method w ith four dielectric constants is developed to study the effect of diel ectric saturation on the electrostatic barriers of the permeation ion. In this method, the inner shape of the channel pore is explicitly rep resented, and the fact that the dielectric constant inside the channel pore is different from that of bulk water is taken into account, A mo del channel system which is a right-handed twist bundle with four alph a-helical segments is provided for this study. From the FDPB calculati ons, it is found that the difference of the ionic electrostatic solvat ion energy for wider domains depends strongly on the pore radius in th e vicinity of the ion when the pore dielectric constant is changed fro m 78 to 5. However, the electrostatic solvation energy of the permeati on ion can not be significantly affected by the dielectric constant in regions with small pore radii. Our results indicate that the local el ectrostatic interactions inside the ion channel are of major importanc e for ion electrostatic solvation energies, and the effect of dielectr ic saturation on the electrostatic barriers is coupled to the interior channel dimensions.