(259b) Molecular Dynamics Study of Pressure Denaturation of Proteins

Studies on the effects of high pressures on biological systems are important from fundamental and applied perspectives. High hydrostatic pressures (~3 kbar) lead to denaturation of proteins. Experiments show that the pressure-induced unfolded conformations of proteins are more compact than the thermally denatured proteins and retain elements of secondary structure. The mechanism of this behavior is, however, yet to be determined. Small solute studies indicate that hydrophobic interactions are weakened at high pressures and solvent-separated configurations are stabilized relative to contact configurations. To extend this understanding to realistic systems such as protein-water systems, simulations of solvated proteins at different pressures are required. However, it is not possible to sample the entire folded-to-unfolded trajectory using brute-force molecular dynamics. Thus, we need to develop novel methods to generate pressure-unfolded structures of proteins. To this end, we have developed an algorithm called forced solvent insertion method to generate pressure unfolded conformations. To demonstrate the utility of this method, we have applied it to the protein Staphnuclease. Using the unfolded conformations of pressure-denatured staphnuclease obtained by our method we calculated the structural change, volume change of unfolding and the Gibbs free energy of unfolding. We find that our results are in good agreement with the experimental data, indicating that the methodology developed in the present work captures the both the structural and thermodynamic aspects of pressure unfolding of proteins. Our study suggests that the mechanism of pressure unfolding involves penetration of water into the hydrophobic core of protein, which leads to the swelling of the hydrophobic core and subsequent unfolding of the protein. Consequently, pressure-unfolded structures are more compact than thermally denatured proteins. The availability of pressure-unfolded structures from molecular simulations provides insights into the factors that contribute to pressure-stability of proteins as well as protein unfolding pathway.