Serine protease (By similarity). Plays a role in innate immunity against infections by parasite P.berghei and by Gram-negative bacteria such as E.coli (PubMed:16188883). In response to P.berghei infection, contributes to the clearing of parasite ookinetes independent of melanization, an innate immune response which consists in the deposition of melanin pigments on invading pathogens and parasites (PubMed:16188883). Secreted in the hemolymph. Expressed by a subpopulation of hemocytes. Expressed in adult females and to a lesser extent in the second and third larval, and pupal stages. Induced by infection with E.coli or S.aureus bacteria. Induced by infection with P.berghei parasite following ookinete invasion of the midgut cells. The clip domain consists of 35-55 residues which are 'knitted' together usually by 3 conserved disulfide bonds forming a clip-like compact structure. N-glycosylated. Proteolytically cleaved. RNAi-mediated knockdown in the G3 strain reduces survival following infection by E.coli bacteria but not following infection by S.aureus bacteria. Following P.berghei infection, the number of parasite oocysts in the gut is increased in the susceptible G3 strain due to a failure to kill or/and lyse ookinetes (the motile parasite zygote that enters the gut to form an oocyst). RNAi-mediated knockdown in the refractory L3-5 strain results in an increase in the number of killed and melanized ookinetes following P.berghei infection. Simultaneous knockdown of lectin CTL4 in the G3 strain (but not in L3-5 strain) causes an increase in the number of developing oocysts and a decrease in melanized ookinetes. Belongs to the peptidase S1 family. CLIP subfamily.