Rao L V, Ruf W
Department of Biochemistry, University of Texas Health Center at Tyler 75710, USA.
Biochemistry. 1995 Aug 29;34(34):10867-71. doi: 10.1021/bi00034a020.
The extrinsic coagulation pathway is initiated by the binding of plasma factor VII(a) (VIIa) to the cell surface receptor tissue factor (TF), which serves as the cofactor for the ligand protease VIIa in the activation of macromolecular substrate factors X and IX. The catalytic function of the TF.VIIa complex is regulated by a specific Kunitz-type inhibitor, tissue factor pathway inhibitor (TFPI), which forms a stoichiometric complex with the serine protease factor Xa (Xa), resulting in greatly accelerated inhibition of the extrinsic initiation complex as compared to free inhibitor. In the present study we identify specific residues in the TF-VIIa complex that are involved in the factor Xa-mediated acceleration of TFPI inhibitory function. VIIa residue Arg290, which contributes to extended recognition of macromolecular substrate factor X, is not involved in the interaction with the TFPI.Xa complex. In contrast, TF residues Lys165 and Lys166, which are important for the activation of factor X, are required for the accelerated inhibition of the TF.VIIa complex by TFPI mediated by factor Xa. These data indicate that similar interactions contribute to the assembly of substrate factor X as well as of product Xa after complex formation with TFPI, suggesting a central role for the carboxyl-terminal structural module of TF in regulating the proteolytic activity of TF.VIIa.
外源性凝血途径由血浆因子VII(a)（VIIa）与细胞表面受体组织因子（TF）结合启动，TF作为配体蛋白酶VIIa激活大分子底物因子X和IX的辅因子。TF.VIIa复合物的催化功能受一种特异性库尼茨型抑制剂——组织因子途径抑制剂（TFPI）的调节，TFPI与丝氨酸蛋白酶因子Xa（Xa）形成化学计量复合物，与游离抑制剂相比，导致对外源性起始复合物的抑制大大加速。在本研究中，我们确定了TF-VIIa复合物中与因子Xa介导的TFPI抑制功能加速有关的特定残基。VIIa残基Arg290有助于对大分子底物因子X的延长识别，不参与与TFPI.Xa复合物的相互作用。相反，对因子X激活很重要的TF残基Lys165和Lys166是TFPI由因子Xa介导加速抑制TF.VIIa复合物所必需的。这些数据表明，类似的相互作用有助于底物因子X以及与TFPI形成复合物后产物Xa的组装，提示TF的羧基末端结构模块在调节TF.VIIa的蛋白水解活性中起核心作用。
