Agglutination activity of Limulus polyphemus coagulogen following limited proteolysis

1. 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. 2. Similar cell agglutination activity can be generated, in vitro, by proteolytic cleavage of the coagulogen with either trypsin, endogenous protease or an α₂M/enzyme complex isolated from amebocytes. 3. 3. Studies with [¹²⁵I]-labeled coagulogen showed that only coagulin, not the intact coagulogen, binds to rabbit erythrocytes and formalin-fixed amebocytes. 4. 4. The cell agglutination activity of coagulin towards erythrocytes was not inhibited by various sugars tested, and was not Ca²⁺-dependent. 5. 5. These findings suggest that coagulogen and coagulin are reminiscent of their mammalian counterparts, fibrinogen and fibrin, in their clotting and relative adhesive properties.