Fancy name for the solvation shell around a protein. Since protein surfaces are covered in hydrophilic groups - sticking out and waving around all over the place - a thin film of ordered water can form. This water coat is only stable compared to the bulk fluid but affects important features of the proteins life. Quaternary interactions are undoubtedly stabilised by the mixture of hydrogen bonds and shell overlap that results. Indeed, many complexes have interface water molecules that bridge essential Hbonds. Some DNA binding proteins, for example, sandwich these water molecules between the protein and the DNA surface.