2.2 Interface and non-interface definition based on atom contacts.
Non-covalent bonding between associating protein units form the interface in-between partnering molecules that form a complex. In this analysis, any pair of residues from the interacting partners, whose atoms fall within a distance of 4.5 Å are considered to form the interfacial sites. This concept is based on proximity and is called an atom contact, is also similar to the method used in the construction of edges to make a structural network of the protein. Any non-adjacent residue within the structural network that comes directly in contact with the interfacial sites by making atom contacts are termed as primary contacts. These sites make up the rim of the interface around the interfacial core. All the remaining residues that are away from the interface makeup the non-interfacial sites.