Serine protease that initiates the GZMK pathway of the complement system, a cascade of proteins directly activated by CD8(+) T-cells that leads to phagocytosis and breakdown of pathogens and signaling that strengthens the adaptive immune system (PubMed:3262682, PubMed:39814882, PubMed:39914456). GZMK is specifically secreted by CD8(+) T-cells and mediates both recognition and initiation steps of GZMK complement pathway (PubMed:39914456). First acts as a pattern recognition receptor, which specifically recognizes and binds heparan sulfate glycosaminoglycans on the pathogen surface to drive opsonization (PubMed:39914456). It then initiates the complement pathway cascade by catalyzing cleavage and activation of C2 and C4, the next components of the complement pathway (PubMed:39814882, PubMed:39914456). GZMK-mediated complement activation is an important contributor to tissue inflammation (PubMed:24711407, PubMed:33271118, PubMed:35704599, PubMed:39614076, PubMed:39814882, PubMed:39914456). Also able to cleave and activate F2R/PAR1 and PAR2/F2RL1, possibly promoting interleukin release (PubMed:21760880, PubMed:26936634, PubMed:35881628). May also regulate apoptosis by catalyzing cleavage and activation of BID, thereby promoting cytochrome C release from mitochrondria (PubMed:17308307). {ECO:0000269|PubMed:17308307, ECO:0000269|PubMed:21760880, ECO:0000269|PubMed:24711407, ECO:0000269|PubMed:26936634, ECO:0000269|PubMed:3262682, ECO:0000269|PubMed:33271118, ECO:0000269|PubMed:35704599, ECO:0000269|PubMed:35881628, ECO:0000269|PubMed:39614076, ECO:0000269|PubMed:39814882, ECO:0000269|PubMed:39914456}. This is the function of ENSG00000113088 (GZMK, granzyme K).