The behavior of liquid water on supercooling has been the subject of a long-standing scientific debate for the past 30 years. It has been found that there are anomalous increases of thermodynamic quantities and apparent divergences of dynamic quantities on approaching a singular temperature of about 230 K at ambient pressure. Very recently it has been also observed that below this temperature a Boson peak emerges in the vibrational spectra of simulated supercooled water [13]. This behaviour has been put in relationship with the crossover to a predominantly low-density-like liquid below the Widom line. A very similar behaviour has been shown as well by protein hydration water, that has been suggested as a model system to study the properties of supercooled water in experimentally unaccessible temperature conditions. Here we propose to investigate the trend of the Boson peak in protein hydration water as a function of the temperature when the Widom line is crossed at different pressure conditions.