Characterization of some molecules in the prophenoloxidase-activating and clotting systems in the freswater crayfish Pacifastacus leniusculus

Sammanfattning: A lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) was purified from crayfish hemocytes. LGBP has binding activity to lipopolysaccharide, curdlan (insoluble β-1,3-glucans) and laminarin (soluble β-1,3-glucans), but not to peptidoglycan. An antibody inhibition assay demonstrated that LGBP was directly involved in the prophenoloxidase (proPO)- activating system. LGBP has significant sequence homology to the earthworm LGBP, the silkworm β-1,3-glucan recognition protein, the insect putative Gram-negative bacteria-binding proteins, and also to the sea urchin and bacterial β-1,3-glucanases.The proPO-activating enzyme (proppA) is a serine proteinase that convertsproP0 to phenoloxidase, which catalyzes the formation of melanin. Crayfish and insect proppAs have clip-like domains at the N-termini. The clip-like domain of the crayfish proppA overexpressed in E. coli exhibited anti-bacterial activity in vitro against Gram-positive bacteria.A clotting protein (CP) in plasma and a transglutaminase (TGase) fromhemocytes are responsible for the coagulation reaction in crustaceans. The crayfish CP is the first cloned crustacean CP representing the second type of clot-forming protein in animal plasma to be characterized and cloned, besides the vertebrate fibrinogens. The crayfish CP is similar to vitellogenins, but it is not a true vitellogenin. The monomeric CP and TGase-crosslinked polymeric CP were visualized by electron microscopy.The crayfish TGase is the first cloned arthropod TGase that has been shown to be directly involved in the clotting system. The crayfish TGase shows 32% identity to its functional equivalent human coagulation factor XIIIa. It is also similar to other arthropod and mammalian TGases.