Revisiting the description of 
		(Protein-Protein) interfaces

The description of non-covalent contacts in (macro-)molecular
assemblies is of fundamental interest for understanding the formation
and the stability of such complexes.  Using atoms loosing solvent
accessibility in the complex or pairs of atoms within a distance
threshold, the description of interfaces focused so far on on shape
complementarity and packing properties at the interface, connectivity
and chemical relationships across the interface, as well as global
measures such as the Surface Area Buried (BSA) upon complex formation,
or the interface planarity.

However, given a complex, no method exist to answer coherently (if at
all) the following questions: can one bridge the gap from atoms
loosing solvent accessibility to interface pairs?  is the interface
flat or curvy?  is it connected or not (does is have a multi-patch
structure)?  is a connected component of the interface simply
connected or not (does the component have a hole or not)?  what is
precisely the role played by interface structural water?  can one
relate interface surface area to Solvent Accessible Surface areas?

We shall present such a method, and discuss selected result for five
classes of protein - protein complexes. The implementation uses the
Delaunay triangulation of CGAL, which processes about one million of
points in about a minute. The construction is therefore suited for
large assemblies.