Mechanisms of Hemostatic Protease Inhibition by Serpins

描述（由申请方提供）：长期目标是确定动脉血栓形成中涉及的丝氨酸蛋白酶抑制剂、肝素辅因子II（HCII）和纤溶酶原激活物抑制剂-1（派-1）抑制凝血酶（T）的分子机制。凝血酶位于纤维蛋白（Fbn）和糖胺聚糖（GAG）、硫酸皮肤素（DS）和肝素上，与HCII和血小板派-1反应，其GAG加速机制不同于抗凝血酶（AT）对凝血酶的抑制，高亲和力肝素加速，仅以痕量存在。与AT不同，HCII是一种独特的动脉血栓形成抑制剂，因为只有在DS存在下HCII才能抑制Fbn结合的凝血酶。假设凝血酶外泌位点I和II在这些过程中发挥不同的作用。外切位点I直接结合HCII和派-1，而外切位点II -肝素结合可调节HCII和派-1周转。这些步骤在T-AT反应中是不存在的.假设DS结合在外部位点II外部作为模板，用于通过HCII抑制外部位点II阻断的凝血酶、甲藻凝血酶（MzT）和MzT（desFI）。本网站的标识; HCII和派-1底物途径; HCII对Fbn结合的凝血酶的DS选择性抑制以及派-1对凝血酶抑制的纤维蛋白原（Fbg）和Fbn调节的机制都是未知的。这些研究将通过使用荧光平衡结合，稳态和快速动力学与天然凝血酶，HCII和派-1，和特定的功能丧失突变体来解决这些重大的差距。他们将测试假设：外部位点的作用在GAG催化的凝血酶失活机制的HCII，派-1和AT是明显不同的; GAG结合外部位点II对凝血酶介导的抑制HCII;和Fbg和Fbn调节凝血酶抑制这些丝氨酸蛋白酶抑制剂的差异。具体目标是：（1）与AT相比，定量在GAG催化的凝血酶失活和HCII和派-1的底物途径中的分子事件序列中的结合和化学步骤;（2）表征凝血酶和MzT中外部位点II外的DS结合位点，及其在凝血酶和MzT抑制中的作用;（3）确定Fbg和Fbn与胞外位点I和GAG的结合在凝血酶保护HCII、派-1和AT中的作用。这些机制为基础的研究是相关的，以了解选择性，局部调节凝血酶活性的HCII和派-1，和丝氨酸蛋白酶抑制剂营业额，在动脉血栓。它们可能有助于开发基于HCII和DS的新型抗凝剂，专门针对动脉血栓形成

DESCRIPTION (provided by applicant): The long-term goal is to define the molecular mechanisms of thrombin (T) inhibition by the serpins, heparin cofactor II (HCII) and plasminogen activator inhibitor-1 (PAI-1), implicated in arterial thrombosis. Thrombin localized on fibrin (Fbn) and the glycosaminoglycans (GAGs) dermatan sulfate (DS) and heparin, reacts with HCII and platelet PAI-1, in GAG-accelerated mechanisms different from thrombin inhibition by antithrombin (AT), accelerated by high affinity heparin, present only in trace amounts. Unlike AT, HCII is a unique inhibitor of arterial thrombosis, as only HCII in the presence of DS is capable of inhibiting Fbn-bound thrombin. Thrombin exosites I and II are hypothesized to play different roles in these processes. Exosite I binds HCII and PAI-1 directly, whereas exosite II - heparin binding may modulate HCII and PAI-1 turnover. These steps are absent in the T - AT reaction. DS bound outside exosite II is hypothesized to act as template for inhibition by HCII of exosite ll-blocked thrombin, meizothrombin (MzT), and MzT(desFI). The identity of this site; the HCII and PAI-1 substrate pathways; the mechanisms of DS-selective inhibition of Fbn-bound thrombin by HCII, and of fibrinogen (Fbg) and Fbn regulation of thrombin inhibition by PAI-1 are all unknown. The studies will resolve these significant gaps, by using fluorescence equilibrium binding, steady-state and rapid kinetics with native thrombin, HCII and PAI-1, and specific loss-of- function mutants. They will test the hypotheses: that the exosite roles in the GAG-catalyzed thrombin inactivation mechanisms by HCII, PAI-1 and AT are distinctly different; that GAG binding outside exosite II on thrombin mediates inhibition by HCII; and that Fbg and Fbn regulate thrombin inhibition by these serpins differentially. Specific aims are: (1) To quantitate binding and chemical steps in the sequence of molecular events in the GAG-catalyzed thrombin inactivation and substrate pathways of HCII and PAI-1, compared to AT; (2) To characterize the DS-binding site outside exosite II in thrombin and MzT, and its role in thrombin and MzT inhibition; and (3) To determine the contributions of Fbg and Fbn binding to exosite I and GAGs in thrombin protection from HCII, PAI-1, and AT. These mechanism-based studies are relevant to understanding the selective, localized regulation of thrombin activity by HCII and PAI-1, and serpin turnover, in arterial clots. They may facilitate development of novel anticoagulants based on HCII and DS specifically targeted to arterial thrombosis