Probable serine protease which plays a role in the innate immune response against parasite P.bergei infection by activating the melanization cascade (PubMed:16922859). In the resistant strain L3-5, involved in the melanization of killed parasite P.berghei ookinetes which results in their clearance (PubMed:16922859). In the susceptible strain G3, appears to be dispensable for ookinete elimination which occurs by lysis (PubMed:16922859). In females, expressed in fat body, cuticle, thorax and ovaries. Expressed in eggs, larvae, pupae, and male and female adults. Induced following a blood meal (PubMed:10469250). Induced in response to bacterial infection (PubMed:10469250, PubMed:10646969). Induced in response to P.berghei infection (PubMed:16922859, PubMed:10646969). The clip domain consists of 35-55 residues which are 'knitted' together usually by 3 conserved disulfide bonds forming a clip-like compact structure. RNAi-mediated knockdown in the resistant strain L3-5 infected with P.berghei, causes a 5-fold reduction in the number of melanized ookinetes (PubMed:16922859). Simultaneous RNAi-mediated knockdown of CLIPB4 and CLIPB17 in the resistant strain L3-5 infected with P.berghei, causes a 52-fold reduction in the number of melanized ookinetes (PubMed:16922859). RNAi-mediated knockdown in the susceptible strain G3 infected with P.berghei has no effect on the response to parasite infection (PubMed:16922859). Simultaneous RNAi-mediated knockdown of CLIPB4 and CTL4 in the susceptible strain G3 infected with P.berghei, abolishes ookinete increased melanization caused by RNAi-mediated knockdown of CTL4 (PubMed:16922859). Belongs to the peptidase S1 family. CLIP subfamily.