Isolation and biological activities of limulus anticoagulant (anti-LPS factor) which interacts with lipopolysaccharide (LPS).

Exposure of limulus hemocytes to bacterial endotoxins (lipopolysaccharide, LPS) results in the activation of the intracellular clotting system, consisting of several protein components. During the separation of these components, a potent anticoagulant, named anti-LPS factor, which inhibits the endotoxin-mediated activation of the coagulation cascade, was found in hemocytes from both Tachypleus tridentatus and Limulus polyphemus (Tanaka, S., et al. (1982) Biochem. Biophys. Res. Commun. 105, 717-723). The principle isolated from the Tachypleus hemocyte lysate by column chromatographies on dextran sulfate-Sepharose CL-6B and Sephadex G-50 under sterile conditions was a simple basic protein with an apparent molecular weight of 15,000. It consisted of a single chain polypeptide containing a total of 128 amino acids. The COOH-terminal end was presumed to be histidine, but no NH2-terminal end reactive to phenylisothiocyanate was detected. The isolated anti-LPS factor specifically inhibited the endotoxin-mediated activation of factor C, which has recently been identified as an LPS-sensitive serine protease zymogen in the hemocytes. This inhibition appeared to be due to the binding of anti-LPS factor with LPS. Moreover, anti-LPS factor had an antibacterial effect on the growth of Gram-negative bacteria (Salmonella minnesota R595 and 1114W) but not on that of Gram-positive bacteria (Staphylococcus aureus 209P). These biological activities of the isolated anti-LPS factor suggest an important role in cellular defence of limulus against microbial invasion.