Co-immunoprecipitation (Co-IP) Assay

The Co-IP assay is a powerful technique that is widely used for the discovery and detection of protein-protein interactions. The principle of this technology is to utilize the antigen-antibody interaction to pull-down putative interactive partners of the target protein. Specifically, the antibody of the target protein is immobilized in affinity resins, which are then exposed to a designed protein mixture, or a cellular extraction. Therefore, proteins or protein complexes that have strong interactions with the target protein will be co-precipitated; and the identities and amounts of these interactive proteins can be revealed by multiple analytical approaches.

The general procedures for a standard Co-IP assay are as follows (Figure 1)

Preparation of protein mixture, cell lysate or tissue extractions
Incubation of protein mixture, cell lysate or tissue extractions with antibody-bound affinity beads
Clearance of unbound proteins with multiple washing steps
Detection of interactive proteins via SDS-PAGE, western blot or mass spectrometry (MS) analysis.
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Co-immunoprecipitation (Co-IP) Assay