Definition of interface and dom-face
An interface is a set of interacting atoms whose Solvent Accessible Surface Area (SASA) is decreased by > 1 Å2 upon the formation of a complex [4]. The SASA for each atom was calculated using MSMS [26] with a probe sphere of radius 1.5 Å. Given a pair of interacting proteins, we define a set of interacting atoms for a single protomer as a face. An interface comprises a pair of interacting faces. We define the set of atoms comprising the face of a single domain as a dom-face. In order to calculate dom-faces, the interfaces extracted from complexes are mapped onto ranges of SCOP 1.65 domain definitions [23]. A total of 354 SCOP domains were extracted related to form the 147 protein complexes considered in our study of the different PPI types, see Table 1.