Binding of Thrombin Activatable Fibrinolysis Inhibitor (TAFI) to Plasminogen May Play a Role in the Fibrinolytic Pathway

摘要

Thrombin activatable fibrinolysis inhibitor (TAFI) or carboxypeptidase U are a carboxypeptidase B-like enzyme. TAFI modulates fibrinolysis by removing lysine and arginine residues from partially degraded fibrin, thereby inhibiting plasmin (Psn)-mediated fibrin degradation. Here, we investigated the binding and activation of TAFI in complex with plasminogen (Pgn) by thrombin (IIa) and thrombomodulin (TM). Bindings of TAFI, activated TAFI (TAFIa), and inactivated TAFIa to Pgn were demonstrated using Pgn-coated plate and anti- TAFI antibody conjugated with HRP in sandwich ELISA format. Next, the retained TAFIa catalytic activities in TAFIa/Pgn complex were monitored by using TAFI chromogenic substrate. In addition, IIa/TM could activate TAFI in the complex with Pgn, indicating the accessibility to its activation site at Arg-92 in the complex. Finally, the TAFI/Pgn complex was immuno-precipitated from pooled normal plasma with TAFI antibody conjugated magnetic beads. Pgn in the complex was detected by HRP conjugated anti-Pgn antibody. Indeed, TAFI/Pgn complex existed and was captured from plasma. Since higher concentration of Pgn existed in plasma than TAFI, most of TAFI isoforms would be bound to Pgn as complex, suggesting the TAFI/Pgn complex as the potential marker in cardiovascular, hemophiliac, or other hemorrhagic diseases.