A novel extracellular protease with fibrinolytic activity from the culture supernatant of Cordyceps sinensis: purification and characterization

A novel serine protease with fibrinolytic activity named CSP was purified from the culture supernatant of the fungus Cordyceps sinensis, a kind of Chinese herbal medicine. Analysis of the purified enzyme by SDS-PAGE indicated that CSP was a single polypeptide chain with an apparent molecular weight of 31 kDa, and N-terminal sequencing revealed that the first ten amino acid residues of the enzyme were Ala-Leu-Ala-Thr-Gln-His-Gly-Ala-Pro-Trp-. When casein was used as a substrate, the proteolytic activity of CSP reached its maximum at pH 7.0 and 40 degrees C. The effect of chemical agents on the enzyme activity indicated that CSP is a serine protease with a free cysteine residue near the active site. It hydrolysed fibrinogen, fibrin and casein with a high efficiency, while hydrolysing bovine serum albumin (BSA) and human serum albumin (HSA) to a lesser extent. CSP was found to be a plasmin-like protease, but not a plasminogen activator, and it preferentially cleaved the A alpha chain of fibrinogen and the alpha-chain of fibrin. Therefore, the extracellular protein CSP may represent a potential new therapeutic agent for the treatment of thrombosis.