  Recently we have shown experimental evidence for a fragile-to-strong dynamic
crossover (FSC) phenomenon in hydration water around a globular protein
(lysozyme) at ambient pressure. In this letter we show that when applying
pressure to the protein-water system, the FSC crossover temperatures in
hydration water of lysozyme tracks the similar Widom line emanating from the
existence of a liquid-liquid critical point in a 1-D confined water (in
MCM-41-S). The mean squared displacements (MSD) of hydrogen atoms in lysozyme
and in its hydration water show a sudden change of slopes at the same
characteristic temperature, which decreases with an increasing pressure. These
results taken together give support of the idea that the dynamic crossover (or
so-called glass transition) of the protein is a function of both temperature
and pressure, following the FSC of its hydration water.
