Physical aspects of the weakly hydrated protein surface

We review the physical properties of water on the surface of weakly hydrated proteins and present some theoretical models used to understand them. The first part concerns mainly structural properties and introduces a model for two-dimensional clusters of water molecules. The second part is devoted to dynamical properties of the hydrated protein surface. Dielectric measurements which provide an evidence for proton conductivity due to the percolation of the network of surface water molecules and for the glass dynamics of migrating protons when temperature is lowered are reviewed. These results can be associated with the concept of frustration and analyzed with two models, an Ising model to describe the proton jumps and the model of two-dimensional surface water which exhibits a glassy dynamiques of the water molecules. Biological implications of these properties of hydration water are briefly discussed.