Mechanisms of amphipathic helical peptide denaturation by guanidinium chloride and urea: a molecular dynamics simulation study

Abstract

Urea and GdmCl are widely used to denature proteins at high concentrations. Here, we used MD simulations to study the denaturation mechanisms of helical peptide in different concentrations of GdmCl and urea. It was found that the helical structure of the peptide in water simulation is disappeared after 5ns while the helicity of the peptide is disappeared after 70ns in 2M urea and 25ns in 1M GdmCl. Surprisingly, this result shows that the helical structure in low concentration of denaturants is remained more with respect to that solvated in water. The present work strongly suggests that urea interact more preferentially to non-polar and aromatic side chains in 2M urea; therefore, hydrophobic residues are in more favorable environment in 2M urea. Our results also reveal that the hydrogen bonds between urea and the backbone is the dominant mechanism by which the peptide is destabilized in high concentration of urea. In 1M and 2M GdmCl, GdmCl molecules tend to engage in transient stacking interactions with aromatics and hydrophobic planar side chains that lead to displacement of water from the hydration surface, providing more favorable environment for them. This shows that accumulation of GdmCl around hydrophobic surfaces in 1M and 2M GdmCl solutions prevents proper solvation of the peptide at the beginning. In high GdmCl concentrations, water solvate the peptide better than 1M and 2M GdmCl. Therefore, our results strongly suggest that hydrogen bonds between water and the peptide are important factors in the destabilization of peptide in GdmCl solutions.