The molecular mechanism of the activation of prophenoloxidase cascade and roles of the cascade on the insect defense

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In the innate immunity of insects three main defense reactions operate, namely a) phagocytosis and encapsulation; 2) the activation of prophenoloxidase cascade and blood doagulation; 3) the induction of anti-fungal and anti-bacterial peptides. Intra-cellular signalling pathways for the induction of anti-fungal and anti-bacterial peptide synthesis have been investigated actively for recent years. However, molecules involved in the recognition of bacterial and fungal cell wall components and the mechanism for the transfer of the recognition signal to cells that synthesize anti-microbial peptides. A receptor, Toll is implicated to work to extra cellular recognition signals to cells and the ligand, spatzle has been shown to be produced from prospatzle by a limited proteolysis. To investigate the protease that is directly responsible for the production of spatzle from prospatzle, we prepared Drosophila prospatzle, prepared anti-spatzle/IgG and homogeneous BAEase that is the active form of a zymogen of protease in prophenoloxidase cascade of the silkworm, Bombyx mori. The BAEEase was shown to hydrolyze a peptide bond of prospatzle resulting in the formation spatzle. This result indicate that prophenoloxidase cascade functions as a recognition system for the induction of anti microbial peptide synthesis.