Activation of thrombin-activable fibrinolysis inhibitor requires epidermal growth factor-like domain 3 of thrombomodulin and is inhibited competitively by protein C.
Thrombomodulin is a cofactor protein on vascular endothelial cells that inhibits the procoagulant functions of thrombin and enhances thrombin-catalyzed activation of anticoagulant protein C. Thrombomodulin also accelerates the proteolytic activation of a plasma procarboxypeptidase referred to as thrombin-activable fibrinolysis inhibitor (TAFI). In this study, we describe structures on recombinant membrane-bound thrombomodulin that are required for human TAFI activation. Deletion of the N-terminal lectin-like domain and epidermal growth factor (EGF)-like domains 1 and 2 had no effect on TAFI or protein C activation, whereas deletions including EGF-like domain 3 selectively abolished thrombomodulin cofactor activity for TAFI activation. Provided that thrombomodulin EGF-like domain 3 was present, TAFI competitively inhibited protein C activation catalyzed by the thrombin-thrombomodulin complex. A thrombomodulin construct lacking EGF-like domain 3 functioned normally as a cofactor for protein C activation but was insensitive to inhibition by TAFI. Thus, the anticoagulant and antifibrinolytic cofactor activities of thrombomodulin have distinct structural requirements: protein C binding to the thrombin-thrombomodulin complex requires EGF-like domain 4, whereas TAFI binding also requires EGF-like domain 3.
Kokame
K
K
Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Zheng
X
X
Sadler
J E
JE
D019943:Amino Acid Substitution; D001667:Binding, Competitive; D025901:Carboxypeptidase B2; D002268:Carboxypeptidases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002460:Cell Line; D004815:Epidermal Growth Factor / Q000378:metabolism*; D006801:Humans; D011486:Protein C / Q000378:metabolism*; D013917:Thrombin / Q000737:chemistry / Q000378:metabolism; D018180:Thrombomodulin / Q000737:chemistry / Q000378:metabolism*
D011486:Protein C; D018180:Thrombomodulin; D004815:Epidermal Growth Factor; D002268:Carboxypeptidases; D025901:Carboxypeptidase B2; D013917:Thrombin