Hypothetical model of caspase-1 regulation of the proPO-AS.
The proPO-AS is known to be localized to granules of the hemocytes and released by exocytosis after activation by microbial polysaccharides, while the final component proPO lacks a signal peptide and is located to the cytoplasm. In this paper we show that a caspase-1 like enzyme is involved in a Ca2+ -dependent release of proPO from the hemocytes and if proPO is not cleaved by the ppA then Caspase1-like enzyme will cleave proPO into two fragments that exhibit bacterial clearance activity and at the same time inactivate the melanin producing enzyme PO. Moreover we show that the peptide that is produced upon activation of proPO to PO by ppA possess high antibacterial and agglutinating activity. In summary this figure shows a putative mechanism for how the ProPO-system is localized to specific sites and is rapidly inactivated to prevent the spread of this dangerous enzyme. GC = granular cell.