Cathepsin C

Cathepsin C (CTSC), also called dipeptidyl peptidase I, is a lysosomal cysteine protease that excises N-terminal dipeptides from protein substrates, distinguishing it from most cathepsins, which act as endopeptidases. The enzyme functions in a chloride-dependent manner and assembles into a homotetramer that is essential for its activity. Its best-established physiological role is the maturation of immune-cell serine proteases, including neutrophil elastase, Cathepsin G, proteinase 3, and granzymes. Inactivating CTSC mutations underlie Papillon-Lefèvre syndrome, characterized by palmoplantar keratoderma and periodontitis, and consequently the protease has become a validated target for developing therapies against neutrophil-driven inflammatory diseases.