Identification of Calpain-Activated Protein Functions

As opposed to proteasome-mediated proteolysis that leads to protein degradation, calpain proteases carry out limited proteolytic cleavages of their substrates. The cleavage of some substrates can produce active fragments that perform functions that are different from those performed by the full-length proteins. Therefore, cleavage by calpains can operate as a posttranslational modification and increase the functional diversity of target proteins. Nevertheless, activation of protein function by calpain cleavage is still an understudied area in molecular biology. Identifying and functionally characterizing by products generated by calpain cleavage could lead to the discovery of biomarkers and the identification of novel drug targets for the treatment of human diseases. This chapter contains a workflow designed to experimentally characterize novel calpain substrates, including identification of potential calpain targets via Western blotting, characterization of calpain cleavage sites, and the study of cellular functions played by such cleaved products. We will employ MYC as an example for these experiments.