Fasciola Hepatica Cathepsin L Proteinase Cleaves Fibrinogen and Produces a Novel Type of Fibrin Clot

A cathepsin L proteinase secreted by the parasitic helminth Fasciola hepatica can cleave fibrinogen and produce a fibrin clot with a specific activity of 4.7 National Institutes of Health thrombin‐equivalent U/mg. This is the first report of a fibrinogen‐clotting activity aside that of thrombin and the snake venom proteinases, which are all serine proteinases. Clot formation by cathepsin L is not inhibited by the thrombin inhibitor hirudin or by the anti‐polymerant H‐Gly‐Pro‐Arg‐Pro‐OH. The enzyme exerts its activity on fibrinogen in a unique manner. Although the cleavage of fibrinogen may involve the initial removal of fibrinopeptides, additional proteolysis of the α, β and γ fibrinogen polypeptides takes place. SDS/PAGE analysis of the cathepsin‐l‐produced clots revealed that cleavage of the α polypeptide (66kDa) precedes that of the β (52kDa) and γ (46.5kDa) polypeptides. Concurrent with the cleavage of these polypeptides is the appearance of components of 120, 100 and 25 kDa. The appearance of higher molecular‐sized components in the cathepsin L clots suggests that polymerisation involves the formation of molecular interactions that are resistant to boiling in mercaptoethanol and SDS.