What are the biological effects of protein-protein interactions?

One effect is that Protein-Protein interactions may modify the kinetic properties of enzymes, which can lead to subtle changes in substrate binding or allosteric effects. Another effect is that PPI can create a novel binding site for small effector molecules. Additionally, PPI can either inactivate or suppress a protein. These protein-protein interactions can change the specificity of a protein for its substrate through interaction with different ligands. For example, they may show a new function that neither protein can exhibit alone. These interactions may also serve as a regulatory function at the downstream or upstream level. PPIs may also act as a general mechanism to permit substrate channeling.