Protein S Regulates Blood Coagulation by Inhibiting Factor IXa

蛋白S（PS）是一种血浆抗凝剂，对维持止血至关重要。 PS中的缺陷或异常可导致血栓性疾病，如肺动脉高压。 栓塞、深静脉血栓形成和急性小血管凝血。PS是一个非 活化蛋白C和组织因子途径抑制物的酶辅因子。最近， 我们发现PS抑制促凝血剂FIXa。这一重要发现可能解释了 与PS缺陷相关的血栓形成病理学。因此，我们试图得出一个完整的 理解FIXa和PS之间的相互作用，并确定 的PS-FIXa相互作用，不包括PS与APC和TFPI的相互作用。识别 PS-FIXa相互作用的生物化学细节将使得能够开发PS的小衍生物， 可以治疗具有过量FIXa活性（和过量血液凝固）和PS的个体 缺陷或异常。 我们已经精确定位了PS结合位点与FIXa的肝素结合位点，并鉴定出HBE PS-FIXa结合所必需的残基。我们已经确定，Gla和EGF结构域的 FIXa有助于与PS相互作用的稳定性，我们发现， PS的层粘连蛋白G1+2结构域是FIXa的有效抑制剂。 对于本项目，我们将使用以下体内和体外方法来实现 彻底理解PS与FIXa的相互作用：（1）确认 FIXa抑制，（2）鉴定FIXa抑制所需的PS残基，和（3）定义体内 FIXa与PS LG结构域和单位点LG结构域突变体的相互作用。的分子和 从这项研究中获得的生物化学知识将为创建PS提供基础， 用于治疗由PS引起的血栓形成病症的衍生的FIX α抑制分子 FIXa缺乏或上调。

Protein S (PS), a plasma anticoagulant, is vital for the maintenance of hemostasis. Deficiencies or abnormalities in PS can lead to thrombotic conditions such as pulmonary embolism, deep vein thrombosis, and acute small blood vessel coagulation. PS is a non- enzymatic cofactor for Activated Protein C and for Tissue Factor Pathway Inhibitor. Recently, we discovered that PS inhibits procoagulant FIXa. This significant finding likely explains the thrombotic pathology associated with PS deficiency. Thus, we seek to derive a complete understanding of the interaction between FIXa and PS and to establish the explicit importance of the PS-FIXa interaction, exclusive of PS interactions with APC and TFPI. Identification of the biochemical details of PS-FIXa interaction will enable development a small derivative of PS that could treat individuals who have excess FIXa activity (and excess blood clotting) and PS deficiencies or abnormalities. We have pinpointed the PS binding site to FIXa’s heparin-binding site and identified HBE residues necessary for PS-FIXa binding. We have established that the Gla and EGF domains of FIXa contribute to the stability of the interaction with PS, and we discovered that the isolated Laminin G1+2 domains of PS are effective inhibitors of FIXa. For this project, we will use the following in vivo and in vitro approaches to achieve a thorough understanding of the interaction of PS with FIXa: (1) Confirm PS domains required for FIXa inhibition, (2) Identify PS residues required for FIXa inhibition, and (3) Define the in vivo interaction of FIXa with PS LG domains and single-site LG domain mutants. The molecular and biochemical knowledge obtained from this study will provide the basis for creation of a PS- derived FIXa-inhibiting molecule for the treatment of thrombotic conditions caused by PS deficiency or upregulation of FIXa.