The crayfish plasma clotting protein: A vitellogenin-related protein responsible for clot formation in crustacean blood

Coagulation in crayfish blood is based on the transglutaminase-mediated cro sslinking of a specific plasma clotting protein. Here we report the cloning of the subunit of this clotting protein from a crayfish hepatopancreas cDN A library. The ORF encodes a protein of 1,721 amino acids, including a sign al peptide of 15 amino acids. Sequence analysis reveals that the clotting p rotein is homologous to vitellogenins, which are proteins found in vitellog enic females of egg-laying animals. The clotting protein and vitellogenins are all lipoproteins and share a limited sequence similarity to certain oth er lipoproteins (e.g., mammalian apolipoprotein B and microsomal triglyceri de transfer protein) and contain a stretch with similarity to the D domain of mammalian von Willebrand factor. The crayfish clotting protein is presen t in both sexes, unlike the female-specific vitellogenins. Electron microsc opy was used to visualize individual clotting protein molecules and to stud y the transglutaminase-mediated clotting reaction. In the presence of an en dogenous transglutaminase, the purified clotting protein molecules rapidly assemble into long, flexible chains that occasionally branch.