A COMBINATORIAL APPROACH DEFINES SPECIFICITIES OF MEMBERS OF THE CASPASE FAMILY AND GRANZYME-B - FUNCTIONAL, RELATIONSHIPS ESTABLISHED FOR KEY MEDIATORS OF APOPTOSIS

There is compelling evidence that members of the caspase (interleukin- 1 beta converting enzyme/CED-3) family of cysteine proteases and the c ytotoxic lymphocyte-derived serine protease granzyme B play essential roles in mammalian apoptosis. Here we use a novel method employing a p ositional scanning substrate combinatorial library to rigorously defin e their individual specificities. The results divide these proteases i nto three distinct groups and suggest that several have redundant func tions. The specificity of caspases 2, 3, and 7 and Caenorhabditis eleg ans CED-3 (DEXD) suggests that all of these enzymes function to incapa citate essential homeostatic pathways during the effector phase of apo ptosis. In contrast, the optimal sequence for caspases 6, 8, and 9 an d granzyme B ((I/L/V)EXD) resembles activation sites in effector caspa se proenzymes, consistent with a role for these enzymes as upstream co mponents in a proteolytic cascade that amplifies the death signal.