Lack of signal peptide in insect prophenoloxidase to avoid glycosylation to damage the zymogen activity.

Insect prophenoloxidases (PPOs) are important immunity proteins for defending against the invading pathogens and parasites. As a Type-Ⅲ copper-containing proteins, unlike Homo sapiens tyrosinases, the insect PPOs and most bacterial tyrosinases contain no signal peptides for unknown reason, however they can still be released. To this end, we fused different signal peptides to Drosophila melanogaster PPOs for in vitro and in vivo expression, respectively.