Agglutination activity of Limulus polyphemus coagulogen following limited proteolysis

1. A 14 kDa protein with cell agglutination properties has been purified from endotoxin-activated L. polyphemus amebocyte lysate. Amino terminal sequence analysis indicates that this protein corresponds to a proteolytically cleaved product (coagulin) of coagulogen. 2. Similar cell agglutination activity can be generated, in vitro, by proteolytic cleavage of the coagulogen with either trypsin, endogenous protease or an alpha 2M/enzyme complex isolated from amebocytes. 3. Studies with [125I]-labeled coagulogen showed that only coagulin, not the intact coagulogen, binds to rabbit erythrocytes and formalin-fixed amebocytes. 4. The cell agglutination activity of coagulin towards erythrocytes was not inhibited by various sugars tested, and was not Ca(2+)-dependent. 5. These findings suggest that coagulogen and coagulin are reminiscent of their mammalian counterparts, fibrinogen and fibrin, in their clotting and relative adhesive properties.