Cytotoxic chymotrypsin-like serine protease with preference for bulky and aromatic residues at the P1 position and acidic residues at the P3' and P4' sites. Probably necessary for target cell lysis in cell-mediated immune responses. Participates in the antiviral response via direct cleavage of several proteins essential for viral replication. Inhibited by SERPINB1. Constitutively expressed in NK cells. Belongs to the peptidase S1 family. Granzyme subfamily.