This domain is found at the N-terminal of cathepsin B and cathepsin B-like peptidases that belong to MEROPS peptidase subfamily C1A. Cathepsin B are lysosomal cysteine proteinases belonging to the papain superfamily and are unique in their ability to act as both an endo- and an exopeptidases. They are synthesized as inactive zymogens. Activation of the peptidases occurs with the removal of the propeptide.