The general goal of these studies is to investigate structural and molecular mechanisms regulating the activation of factor IX via the tissue factor pathway of coagulation and to further delineate the functions of different domains of factor IX. Tissue factor pathway inhibitor (TFPI) consists of three kunitz-type domains. The first domain binds to factor VIIa and the second domain binds to factor Xa. The function of the third domain is as yet not clear. In the proposed studies, attempts will also be made to delineate the function of the third domain of TFPI. By sequencing the gene, we will define the molecular basis of TFPI deficiency in patients who have been identified to contain 50% (or less) of normal plasma levels of TFPI. Both of them have had thrombotic episodes and are normal with respect to other known anticoagulant and fibrinolytic mechanisms. In other experiments, we will further examine whether or not the protease domain of factor IXa contains a part of the binding site for factor VIIIa. Likewise, whether or not the protease domain of factor Ixa also interact with factor VIIIa will be investigated. We will also test a hypothesis that the EGF-1 and/or EGF-2 domain of factor IX is needed for its activation by the tissue factor/factor VIIa complex. We anticipate that the information obtained from the proposed studies will significantly enhance our understanding about the molecular mechanisms involved in the assembly of intrinsic factor X-activating complex. In addition, the studies will define the molecular basis of TFPI deficiency in the patients investigated.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
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Hematology Subcommittee 2 (HEM)
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Saint Louis University
Schools of Medicine
Saint Louis
United States
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Kumar, Yogesh; Vadivel, Kanagasabai; Schmidt, Amy E et al. (2014) Decoy plasminogen receptor containing a selective Kunitz-inhibitory domain. Biochemistry 53:505-17
Vadivel, Kanagasabai; Ponnuraj, Sathya-Moorthy; Kumar, Yogesh et al. (2014) Platelets contain tissue factor pathway inhibitor-2 derived from megakaryocytes and inhibits fibrinolysis. J Biol Chem 289:31647-61
Vadivel, Kanagasabai; Agah, Sayeh; Messer, Amanda S et al. (2013) Structural and functional studies of ?-carboxyglutamic acid domains of factor VIIa and activated Protein C: role of magnesium at physiological calcium. J Mol Biol 425:1961-1981
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Geng, Yipeng; Verhamme, Ingrid M; Messer, Amanda et al. (2012) A sequential mechanism for exosite-mediated factor IX activation by factor XIa. J Biol Chem 287:38200-9
Bajaj, Madhu S; Ogueli, Godwin I; Kumar, Yogesh et al. (2011) Engineering kunitz domain 1 (KD1) of human tissue factor pathway inhibitor-2 to selectively inhibit fibrinolysis: properties of KD1-L17R variant. J Biol Chem 286:4329-40
Messer, A S; Velander, W H; Bajaj, S P (2009) Contribution of magnesium in binding of factor IXa to the phospholipid surface: implications for vitamin K-dependent coagulation proteins. J Thromb Haemost 7:2151-3
Agah, S; Bajaj, S P (2009) Role of magnesium in factor XIa catalyzed activation of factor IX: calcium binding to factor IX under physiologic magnesium. J Thromb Haemost 7:1426-8
Schmidt, Amy E; Sun, Mao-fu; Ogawa, Taketoshi et al. (2008) Functional role of residue 193 (chymotrypsin numbering) in serine proteases: influence of side chain length and beta-branching on the catalytic activity of blood coagulation factor XIa. Biochemistry 47:1326-35
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