3.3 A tie between hydrophobic interactions and hydrogen bonds: permanent and transient domains
It is clear from the previous analysis that permanent domains have a larger number of interactions between interacting domains than transient domains. To obtain a clearer perspective on the interactions, we probed atomic interactions of interfacial residues. We observed around 52% of the total number of interactions in the case of proteins having permanent domains are hydrophobic (Figure 3A). On the contrary, as shown in Figure 3B, transient domains have only 37% of hydrophobic interactions. These hydrophobic interactions are known to drive different PPIs and are known to comprise major interactions in the biomolecules which stabilize interacting complexes. Moreover, we found that transient domains have large proportions of side chain associated hydrogen bonds in comparison to permanent domains (Figure 3A, 3B and Supplementary Figure S1), and such polar interactions are known to bring out specificity. Apart from hydrophobic interactions and side chain associated hydrogen bonds, all other interaction types were similarly populated in the interface, which would be required for sustained domain interactions and the functioning of multi-domain proteins.