Polarization effects on peptide conformations at water-membrane interface by molecular dynamics simulation

The electrostatic image method was applied to investigate the conformation of peptides characterized by different hydrophobicities in a water-membrane interface model. The interface was represented by a surface of discontinui ty between two media with different dielectric constants, taking into accou nt the difference between the polarizabilities of the aqueous medium and th e hydrocarbon one. The method consists of a substitution of the real proble m, which involves the charges and the induced polarization at the surface o f discontinuity, by a simpler problem formed with charges and their images. The electric field due to the polarization induced at the surface by charg e q was calculated using a hypothetical charge q' (image of q), symmetrical ly located on the opposite side of the surface. The value of q' was determi ned using the appropriate electrostatic boundary conditions at the surface. By means of this procedure, the effect of the interface can be introduced easily in the usual force field. We included this extension in the computat ional package that we are developing for molecular dynamics simulations (TH OR). The peptides studied included hydrophilic tetraaspartic acid (Asp-Asp- Asp-Asp), tetralysine (Lys-Lys-Lys-Lys), hydrophobic tetrapeptide (His-Phe- Arg-Trp), an amphiphilic fragment of beta-endorphin, and the signal sequenc e of the E. coli lambda-receptor. The simulation results are in agreement w ith known experimental data regarding the behavior of peptides at the water -membrane interface. An analysis of the conformational dynamics of the sign al sequence peptide at the interface was performed over the course of a few nanoseconds. (C) 1999 John Wiley & Sons, Inc.