 Specifically, there are three hydrophobic residues within the binding domain of E3BP - Pro133, Pro154, and Ile157 – that interact with the surface of both E3 polypeptide chains.This interaction is significantly stabilized by many ionic and hydrogen bonds that take place between the residues of three interacting polypeptide chains adjacent to the central hydrophobic patch.This specificity is most likely due to the lack of conformational flexibility of the binding fragment of E3BP and the complementary amino acid match with the E3 interface.