Modeling of macromolecular proteins in prophenoloxidase cascade through experimental and computational approaches.

Prophenoloxidase (ProPO) cascade is a principal defense system in crustaceans, which consists of a variety of pattern recognition proteins (lipopolysaccharide and β-glucan-binding protein [β-GBP], β-GBP, and β-glucan recognition protein), proteases (serine protease), and protease inhibitors (α2-macroglobulin and pacifastin) to regulate the protection mechanism in crustaceans. In the prophneoloxidase pathway, the protein-protein interactions (PPIs) and other immune-related analyses still have not been reported. Moreover, the structural features of ProPO cascade proteins have not yet been reported, hence we constructed the three-dimensional structural features for all ProPO pathway proteins. Their PPIs were studied through an in silico approach. Laminarin has been identified as a triggering activator and it showed energetic binding with homology modeled β-GBP and activated the β-GBP, followed by the protein-protein complex formation leading to phenoloxidase synthesis. These findings provided a novel view of the ProPO mechanism and enhanced our knowledge of the innate immune system in crustaceans via computation. In conclusion, we propose a combined experimental and computational approach to analyze the mechanism of ProPO cascade proteins.