IP

Immunoprecipitation

Immunoprecipitation (IP) is a technique used to remove proteins from a sample thanks to their affinity with a specific antibody. The biological matrix of the sample may be highly complex with thousands of proteins and other biomolecules. IP enables to isolate one. In IP the antibodies are bound to solid surfaces, often shaped as beads, that can be removed from the studied sample. There are several types of sub applications of immuno-precipitation given the nature of the product.

Protein Complex Immunoprecipitation

Protein Complex Immunoprecipitation (Co-IP), targets complexes of proteins. One protein of the complex is the antigen of the IP antibody. The whole complex can be precipitated thanks to the affinity of the antibody for its antigen and the affinity of the complexed proteins. This “pull-down” may enable to analyze other proteins belonging to the complex that were not previously known. This technique requires the epitope not to be hidden within the complex. Moreover, if the molecules are not tightly bound, results may be difficult to analyze. This is increased with the complexity of the proteins structure.

Chromatin Immunoprecipitation

Chromatin Immunoprecipitation (ChIP) describes the IP applied to DNA. It is especially used to determine the DNA binding site of the targeted protein. Similarly to Co-IP, complexes are bound to antibodies thanks to the affinity of an antibody for its antigen. In the case of ChIP, the antigen is cross-linked with DNA. Once the complex is removed from the sample, the crosslinking may be eliminated to get the specific DNA fragment. This fragment may then be sequenced with Polymer Chain Reaction (PCR) for example.

Tagged Protein IP

As generating an antibody specific enough for a protein belonging to a complex may not be easy, antibodies may be generated against tags that are bound to proteins. However this tag may impact the interaction of the complex, either destabilizing the preexisting bonds or creating new ones.