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 mec hanics (Hartree-Fock 6-31G**) with solvation in the Poisson-Boltzmann conti nuum solvent approximation. We find that aqueous solvent preferentially sta bilizes the alpha-helix conformation over beta-sheet conformations by 3.5 k cal/mol for Ala. 2.4 kcal/mol for Gly, and 2.0 kcal/mol for Pro. We determi ned the torsional potential surfaces of the tripeptides. Gly-Ala-Gly, Gly-G ly-Gly, and Gly-Pro-Gly using both aqueous solvent and nonpolar solvent con ditions. These results were used to determine force-field torsional paramet ers for the protein main chains.