Caspase

Definition

Are protein degrading enzymes (proteases) that act as mediators of programmed cell death (apoptosis). Proteins within the large family of these cell-death proteases are all similar to each other. Caspases are highly conserved during evolution and can be found in humans as well as in insects and worms and are even found in lower multicellular organisms. More than a dozen caspases have been identified in humans. Usually caspases selectively cleave a restricted set of target proteins in the primary sequence at one position, or at a few positions at most. Cleavage always occurs behind an aspartate amino acid. The caspase-mediated cleavage of specific substrates supplies an explanation for several characteristic features of apoptosis. Cleavage of the nuclear lamins, for instance, is required for nuclear shrinking. Cleavage of cytoskeletal proteins causes the overall loss of cell shape. In healthy cells, caspases normally lie dormant. In response to diverse stimuli, they become...