Binds and activates processed prophenoloxidases PPO1 and PPO2 and thus is involved in the activation of the prophenoloxidase cascade probably following the recognition of pathogen-derived products (By similarity). Binds the A.niger cell wall component alpha-1,3-glucan, a fungal pathogen-associated molecular pattern (PAMP) that activates the host immune response (PubMed:34443685). Heterodimer. Secreted in the hemolymph. Expressed in last instar larvae. Belongs to the peptidase S1 family. Lacks the conserved Ser residue within the catalytic triad which is replaced by a Gly residue, probably resulting in a loss of proteolytic activity.