In Vitro Cleavage Assays using Purified Recombinant Drosophila Caspases for Substrate Screening.

Caspases are very specific cell death proteases that are involved in apoptotic and non-apoptotic processes. While the role of caspases during apoptosis has been very well defined and many apoptotic proteolytic substrates of caspases have been identified and characterized, the role of caspases for non-apoptotic processes is not well understood. In particular, few non-apoptotic substrates of caspases have been identified thus far. Here, in order to facilitate the identification and characterization of potential caspase substrates, a protocol that allows the testing of candidate substrates in caspase cleavage assays in vitro is described. This protocol includes the production and purification of recombinant caspase proteins, the production of the candidate substrates either recombinantly or in a cell-free expression system, and the actual in vitro cleavage reaction followed by SDS-PAGE and immunoblotting. This protocol is tailored for the Drosophila caspases Dronc and Drice but can easily be adapted for caspases from other organisms, including mammals.