5.4 Protein–protein interactions
You should by now be beginning to appreciate the importance of protein–protein interactions in different cellular processes. Indeed, such interactions are intrinsic to virtually every cellular process, e.g. DNA replication, transcription, translation, control of the cell cycle, signal transduction, secretory and metabolic processes.
There are three main types of protein–protein interaction, termed surface–string, helix–helix and surface–surface interactions (Figure 37).
Surface–surface interactions are the most common type of protein–protein contact. They require precise matching of complementary surfaces in the two proteins and tend to be relatively strong. The requirement for a good fit makes surface–surface interactions very specific.
In surface–string interactions, an extended loop of one protein makes contact with the surface of another protein. An example of this kind of interaction is that which occurs between a peptide containing a phosphotyrosine residue and the SH2 domain of Src and other related proteins. Another surface–string interaction takes place between the kinase fold of Src and part of the protein that it phosphorylates.
Helix–helix interactions involve α helices from two different proteins wrapping around each other to form a coiled-coil. Such an interaction occurs in a number of gene-regulatory proteins. Towards the end of this free course we will look at some of the techniques employed to study protein–protein interactions.