Water Mediated Interactions and the Protein Folding Phase Diagram in the Temperature-Pressure Plane

BJ Sirovetz and NP Schafer and PG Wolynes, JOURNAL OF PHYSICAL CHEMISTRY B, 119, 11416-11427 (2015).

DOI: 10.1021/acs.jpcb.5b03828

The temperature pressure behavior of two proteins, ubiquitin and lambda- repressor, is explored using a realistically coarse-grained physicochemical model, the associative memory, water mediated, structure and energy model (AWSEM). The phase diagram across the temperature pressure plane is obtained by perturbing the water mediated interactions in the Hamiltonian systematically. The phase diagrams calculated with direct simulations along with an extended bridge sampling estimator show the main features found experimentally, including both cold- and pressure-denaturation. The denatured ensembles in different parts of the phase diagram are characterized and found to be structurally distinct. The protein energy landscape is found to be funneled throughout the phase diagram, but modest changes in the entropy and free energy of the water are found to drive both cold and pressure induced denaturation.

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