Effect of thrombomodulin on plasminogen activation

Thrombomodulin (TM), a thrombin receptor on the endothelial cell surface, plays an important role in the regulation of blood coagulation. In this study, recombinant TM containing six epidermal growth factor-like structures (D2), and serine and threonine (Ser/Thr)-rich domain (D3), TMD23 (corresponding to Ala224-Ser497), was prepared by a recombinant baculovirus expression system and purified to apparent homogeneity by DEAE-Sepharose CL-6B and affinity nickel-chelating column chromatographies. TMD23 in combination with thrombin could effectively activate protein C. TMD23 alone could enhance Glu-plasminogen activation by single-chain urokinase-type plasminogen activator in a dose-dependent manner. The specific binding of plasminogen to TMD23 was also demonstrated and the binding was inhibited by ε-aminocaproic acid. In conclusion, our results suggest that TMD23 could specifically bind to plasminogen and effectively enhance plasminogen activation.