The calpain-system of Drosophila melanogaster: coming of age.

Drosophila melanogaster is one of the most popular and powerful model organisms that help our understanding of mammalian (human) life processes at the molecular level. Calpains are Ca(2+)-activated cytoplasmic proteases thought to play multiple roles in intracellular signal processing by limited proteolysis of target substrate proteins, thereby changing their function. The calpain superfamily consists of 14 genes in mammals, but only 4 genes in Drosophila. One may assume that the calpain system, i.e. recognizing calpain-dependent life processes and identifying the substrates cleaved while exerting their functions, would prove easier to solve in Drosophila than in mammals. Recently, major progress has been made in characterizing Drosophila Calpain A, Calpain B and Calpain C. The fourth member, Calpain D (or SOL), was analyzed earlier. At this juncture, it seems justifiable to summarize our knowledge about the Drosophila enzymes, in comparison to the ubiquitous mammalian ones, as regards structure-function relations, mode of activation by Ca(2+) and other factors, inhibition, potential targeting, expression pattern in vivo, etc. Equipped with all this information, we may now embark on the genetic modification of family members, interpreting mutant phenotypes in terms of the cell biology of calpains.