Co-immunoprecipitation

Co-immunoprecipitation (Co-IP) is the immunoprecipitation of intact protein complexes (i.e. antigen along with any proteins or ligands that are bound to it; Figure 5). Co-IP works by selecting an antibody that targets a known protein that is believed to be a member of a larger complex of proteins. By targeting this known member of a complex with an antibody, you might be able to pull the entire protein complex out of solution and thereby identify unknown members of the complex.

This technique works when the proteins involved in the complex bind to each other tightly, making it possible to pull multiple members of the complex out of solution by latching onto one member with an antibody.

Co-IP has been traditionally considered as the “gold standard” assay for protein-protein interactions, but its caveats are very similar to those of AP-MS as it is also an affinity purification method.