  The mechanism of cold- and pressure-denaturation are matter of debate. Some
models propose that when denaturation occurs more hydrogen bonds between the
molecules of hydration water are formed. Other models identify the cause in the
density fluctuations of surface water, or the destabilization of hydrophobic
contacts because of the displacement of water molecules inside the protein, as
proposed for high pressures. However, it is clear that water plays a
fundamental role in the process. Here, we review some models that have been
proposed to give insight into this problem. Next we describe a coarse-grained
model of a water monolayer that successfully reproduces the complex
thermodynamics of water and compares well with experiments on proteins at low
hydration level. We introduce its extension for a homopolymer in contact with
the water monolayer and study it by Monte Carlo simulations. Our goal is to
perform a step in the direction of understanding how the interplay of
cooperativity of water and interfacial hydrogen bonds affects the protein
stability and the unfolding.
