You performed a coimmunoprecipitation experiment to identify

You performed a co-immunoprecipitation experiment to identify cellular proteins associated with protein X. For the experiment, you used antibodies against protein X that were immobilized on beads. You incubated these beads with cell lysates from either wild-type cells or cells lacking the gene encoding protein Y. After washing and eluting the bound protein off the beads, you separated each bound and unbound fraction by SDS-PAGE. Finally, you performed immunoblotting using antibodies against either protein Y or protein Z. The results of the Western blots are presented in the following schematic drawings. According to these results, do you think protein Y enhances (E) or inhibits (I) binding of protein X to protein Z?

Solution

Co immunoprecipitation is a technique which identifies which identifies protein interactions that are similar or physiologically relevant . This is done by using target proteins that are specific to the antibodies which would indirectly capture the proteins that would bind to the target protein . This is generally done to identify or isolate a particular protein.

In this experiment, we need to check the protein protein interaction of preotein X and protein Z in the presence of bound and unbound protein Y. Here , in the western blot result , we observe that in the first lane where there is a wild type strain ,which contains the Y protein , there is a presence of a thick band at the bound lane , and no band at the unbound lane . This result clearly shows that the presence of a bound Y protein in the gel , enhances the interaction of Z with X.

But the anomaly comes when we are seeing the Y null lane. Here the unbound Y null gives a high band whereas the bound Y null gives a thin band , but does produce a band. This shows , that the binding of a null Y protein produces a thinner band as compared to the band given by a bound Y protein . This result clearly indicates that the binding of the Y protein enhances the Z and X protein interaction. But , this also shows that the null Y protein inhibits the interaction of Z and X , as in unbound form it gives a thicker band as compared to the bound form.