initiator caspases

Caspases, the principal effectors of apoptosis, are conserved in metazoans. These proteolytic enzymes are remarkable in their exquisite substrate specificity, cleaving the peptide bond after an Asp residue. Procaspase zymogens consist of an N-terminal prodomain followed by large and small subunits. Upon receipt of an apoptotic stimulus, proteolytic processing of the caspase generates the large and small subunits of the catalytic domain which are arranged as a dimer of heterodimers.