Salt effects on the conformational preferences of alanine peptides

ELIANA K. ASCIUTTO; JEFFRY D. MADURA

Philadelphia

Congreso; American Chemical Society National Meeting 2008; 2008

American Chemical Society

The behavior of proteins in salt solutions constitutes a fundamental basis in the study of protein folding. Protein dynamics depends on the environment and the inclusion of salts in the simulation of folding/unfolding becomes extremely necessary when comparing energy barriers or reaction rates with experimental results. Recent experimental unfolding studies have been performed with helical peptides in solutions containing differing concentrations of sodium perchlorate NaClO4. In this work we investigated the effects of NaClO4 on helical peptide conformations, using molecular dynamics simulations of a mainly alanine based peptide (AP) immersed in NaClO4, NaCl and TIP3P water. We compared the unfolding dynamics and found that NaClO4 solution strongly stabilizes the peptide's α-helix like conformations while NaCl solution has a slight destabilizing effect. We investigated the possible (des) stabilizing mechanisms involved and found no direct ion binding processes or evidence of electrostatic screening between the arginine side-chains and the ions. Using a Kirkwood-Buff approach, preferential interaction parameters (Γ) were calculated and used to determine the change upon unfolding of the preferential interaction, ΔΓ(F→U). We found that |ΔΓNaClO4F→U | >> |ΔΓNaClF→U | , representing a preferential water hydration favored by the folded peptide when immersed in NaClO4 solution.