Redirecting the Peptide Cleavage Causes Protease Inactivation

Cysteine and serine proteases cleave peptides through covalent catalysis by generating a transient adduct with the N-terminal part of the substrate after releasing its C-terminal part. We demonstrate the unique redirection of this event leading to strong enzyme inactivation. For targeting human cathepsin B, a cysteine protease of significant therapeutic importance, we designed tailored peptidomimetics with a variety of dipeptide fragments directed toward the occluding loop and equipped with numerous N-terminal carbamate warheads. The carbamate deprotonation catalyzed by the active site thiolate initiates the redirected cleavage. The C-terminal part of the inhibitors remains covalently attached to the protease. Hydrolysis of such carbamoyl-enzyme complexes is catalytically unsupported rendering inhibition irreversible. This novel mechanism of action comprises a significant extension of the covalent drug space.