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.