Co-immunoprecipitation from transfected cells.

Co-immunoprecipitation (Co-IP) is one of the most widely used methods to identify novel proteins that associate with a protein of interest or to determine complex formation between known proteins. For this technique, a protein of interest is captured using a specific antibody. The antibody-bound protein, as well as any proteins bound to the protein of interest, is then precipitated using a resin (immunoprecipitation, IP). Proteins that are not bound to the protein of interest are then removed from the sample with a series of washes. The resulting immunocomplexes are then analyzed by immunoblot. As the requirements for protein-protein interactions vary, optimal experimental conditions for examining the interacting partners of different proteins of interest must be determined empirically. Once appropriate experimental conditions have been established, the IP/Co-IP procedure is simple and straightforward. In this chapter, a standard protocol for IP/co-IP, with several key factors for the success of IP/co-IP analyses, is discussed.