Differential responses in the core, active site and peripheral regions of cytochrome c peroxidase to extreme pressure and temperature

In consideration of life in extreme environments, the effects of hydrostatic pressure on proteins at the atomic level have drawn substantial interest. Large deviations of temperature and pressure from ambient conditions can shift the free energy landscape of proteins to reveal otherwise lowly populated structural states and even promote unfolding. We report the crystal structure of the heme-containing peroxidase, cytochrome c peroxidase (CcP) at 1.5 and 3.0 kbar and make comparisons to structures determined at 1.0 bar and cryo-temperatures (100 K). Compressibility plateaus after 1.5 kbar and pressure produces anisotropic changes in CcP. CcP responds to pressure with volume declines at the periphery of the protein where B-factors are relatively high but maintains nearly intransient core structure and active site channels. Compression at the surface affects neither alternate side-chain conformers nor B-factors. Thus, packing in the core, which resembles a crystalline solid, limits motion and protects the active site, whereas looser packing at the surface preserves side-chain dynamics. Changes in active-site solvation and heme ligation reveal pressure sensitivity to protein-ligand interactions and reveal a potential docking site for the substrate peroxide.