Metacaspase 2 of Trypanosoma brucei is a calcium-dependent cysteine peptidase active without processing

Metacaspases are cysteine peptidases that are distantly related to the caspases, for which proteolytic processing is central to their activation. Here, we show that recombinant metacaspase 2 (MCA2) from Trypanosoma brucei has arginine/lysine-specific, Ca(2+)-dependent proteolytic activity. Autocatalytic processing of MCA2 occurred after Lys55 and Lys268; however, this was shown not to be required for the enzyme to be proteolytically active. The necessity of Ca(2+), but not processing, for MCA2 enzymatic activity clearly distinguishes MCA2 from the caspases and would be consistent with different physiological roles.