2.2. Amino acid residues interaction analysis
The web server of Protein Contacts Atlas( http://www.mrc-lmb.cam.ac.uk/pca/) was applied for analysis of non-covalent contacts, such as hydrogen bonds, hydrophobic interactions, cation-pi interactions, salt bridges, and etc. The default threshold of the atoms’ distance for interaction calculations is set as 0.5 Å. Multiple non-covalent contacts at different scales of structure, namely, amino acid residues, secondary structure, subunits, and entire complexes were analyzed[19]. Protein side-chain networks (PScN) is then constructed by setting amino acid residues as nodes. The edges are constructed between the nodes based on non-covalent interactions, side-chain interaction between them.