Maintenance of caspase-3 proenzyme dormancy by an intrinsic "safety catch"regulatory tripeptide

Caspase-3 is synthesized as a dormant proenzyme and is maintained in an ina ctive conformation by an Asp-Asp-Asp "safety-catch" regulatory tripeptide c ontained within a flexible loop near the large-subunit/smaIl-subunit juncti on. Removal of this "safety catch" results in substantially enhanced autoca talytic maturation as well,as increased vulnerability to proteolytic activa tion by upstream proteases in the apoptotic pathway such as caspase-9 and g ranzyme B. The safety catch functions through multiple ionic interactions t hat are disrupted by acidification, which occurs in the cytosol of cells du ring the early stages of apoptosis. We propose that the caspase-3 safety ca tch is a key regulatory checkpoint in the apoptotic cascade that regulates terminal events in the caspase cascade by modulating the triggering of casp ase-3 activation.