Biological activities of granzyme K are conserved in the mouse and account for residual Z‐Lys‐SBzl activity in granzyme A‐deficient mice

Tryptase‐like activities of T and NK cells contribute to the induction of target cell apoptosis, but only granzyme A (GzmA) has been shown to exhibit Z‐Lys‐SBzl esterase activity in murine T cells. GzmA‐deficient mice exhibit residual Z‐Lys‐SBzl hydrolyzing activity and almost normal levels of lymphocyte‐mediated cytotoxicity. Here we report the cloning and biochemical characterization of recombinant mouse granzyme K (GzmK). The purified murine protein shows Z‐Lys‐SBzl hydrolyzing activity and is inhibited by bikunin, the light chain of inter‐α‐trypsin inhibitor, like the human homolog. We conclude that GzmK expressed by GzmA‐deficient T cells accounts for the remaining Z‐Lys‐SBzl activity. Functional similarities between GzmA and GzmK may explain the subtle immunological deficits observed in GzmA‐deficient mice.