A calpain-like activity insensitive to calpastatin in Drosophila melanogaster.

Calpains are neutral Ca2+-dependent cysteine proteases. In this study, we utilized casein zymography to detect such a proteolytic activity in Drosophila melanogaster extracts throughout the life of this organism. One calpain-like activity that was sensitive to the general cysteine protease inhibitors, E64 and calpain inhibitor I, but insensitive to the human calpain-specific inhibitor, calpastatin, is demonstrated. The relevance of this finding is discussed with respect to the absence of a corresponding Drosophila gene, homologous to the vertebrate calpastatin genes, as concluded from our unsuccessful attempts to clone such a gene and our Blast searches using the FlyBase. The mechanisms of Drosophila calpain regulation require further investigation. However, we suggest that single chain, non-heterodimeric calpains may be insensitive to calpastatin and that Drosophila cystatin-like molecules may play a role in negatively regulating Drosophila calpain.