  We present a coarse-grained lattice model to study the influence of water on
the recognition process of two rigid proteins. The basic model is formulated in
terms of the hydrophobic effect. We then investigate several modifications of
our basic model showing that the selectivity of the recognition process can be
enhanced by considering the explicit influence of single solvent particles.
When the number of cavities at the interface of a protein-protein complex is
fixed as an intrinsic geometric constraint, there typically exists a
characteristic fraction that should be filled with water molecules such that
the selectivity exhibits a maximum. In addition the optimum fraction depends on
the hydrophobicity of the interface so that one has to distinguish between dry
and wet interfaces.
