Serine protease which, by converting prophenoloxidase 1 (PPO1) into its active form, plays an essential role in the melanization immune response to physical or septic wounding. May function in diverse PPO1-activating cascades that are negatively controlled by different serpin proteins; Spn27A and Spn28D in the hemolymph, and Spn28D and Spn77BA in the trachea. Also required in the systematic wound response by mediating the redox-dependent activation of the JNK cytoprotective cascade in neuronal tissues after integument wounding. Up-regulated after wounding to the integument. Levels are higher with septic wounding, using either Gram-negative or Gram-positive bacteria. The clip domain consists of 35-55 residues which are 'knitted' together usually by 3 conserved disulfide bonds forming a clip-like compact structure. Viable and fertile with no obvious phenotype. Reduced adult survival after wounding of the thorax, especially when the injury completely penetrates the thorax (strong wound). Wounding coupled with septic infection (septic injury) does not further reduce survival. Survival after wounding is increased when flies ingest the oxidant paraquat. Impaired melanization at the wound site. In pupae, aseptic and septic-injury does not induce the cleavage of PPO1, and in adults and larvae PPO1 activity is abolished. Belongs to the peptidase S1 family. CLIP subfamily. Extended N-terminus.