Solvent effects on the secondary structures of proteins

We examined the effect of solvation on the conformational preferences (e.g., alpha-helix versus beta-sheet) of tripeptides using ab initio quantum mechanics (Hartree-Fock 6-31G**) with solvation in the Poisson-Boltzmann continuum solvent approximation. We find that aqueous solvent preferentially stabilizes the alpha-helix conformation over beta-sheet conformations by 3.5 kcal/mol for Ala. 2.4 kcal/mol for Gly, and 2.0 kcal/mol for Pro. We determined the torsional potential surfaces of the tripeptides. Gly-Ala-Gly, Gly-Gly-Gly, and Gly-Pro-Gly using both aqueous solvent and nonpolar solvent conditions. These results were used to determine force-field torsional parameters for the protein main chains.