Computing the stability diagram Trp-cage miniprotein of the

We report molecular dynamics simulations of the equilibrium folding/unfolding thermodynamics of an all-atom model of the Trp-cage miniprotein in explicit solvent. Simulations are used to sample the folding/unfolding free energy difference and its derivatives along 2 isochores. We model the Delta G(u)(P,T) landscape using the simulation data and propose a stablility diagram model for Trp-cage. We find the proposed diagram to exhibit features similar to globular proteins with increasing hydrostatic pressure destabilizing the native fold. The observed energy differences Delta E-u are roughly linearly temperature-dependent and approach Delta E-u = 0 with decreasing temperature, suggesting that the system approached the region of cold denaturation. In the low-temperature denatured state, the native helical secondary structure elements are largely preserved, whereas the protein conformation changes to an open-clamp configuration. A tighter packing of water around nonpolar sites, accompanied by an increasing solvent-accessible surface area of the unfolded ensemble, seems to stabilize the unfolded state at elevated pressures.