Method of the Month — Immunoprecipitation
July 2021
Immunoprecipitation (IP) is a technique that is used to separate and study a protein of interest. IP can be used to isolate a specific protein from a sample that may contain hundreds or thousands of other proteins. If you break the word down, you can get an idea of how this works. “Immuno-” refers to the method of using a specific antibody to bind a particular protein (think how our immune system “remembers” pathogens it’s encountered before). The “precipitation” part of the word refers to precipitating (or separating) that antibody-bound protein out of the solution. This technique is relatively simple, but essential to research.
You begin the process by adding your antibody to the solution where it binds the protein of interest. But now you need something to separate your proteins from the others. There are multiple ways to accomplish this, and one method uses agarose beads with special proteins called A/G proteins attached. These A/G proteins bind your protein-antibody complexes via the Fc region on the antibody (which is basically the “tail” end of the antibody). Now the entire solution can be washed to eliminate the unbound, unwanted proteins, and purified so that only the beads and your attached proteins remain.
Now if you wanted to determine which proteins bind to others, a similar method can be applied. Co-immunoprecipitation utilizes the same technique as IP, but uses an antibody specific to your target protein that not only isolates that target protein, but any other proteins bound to the target. The technique applies the original isolation process while also allowing a researcher to determine protein-protein interactions. An example of this research technique can be found in an article summary here.
