蛋白S（PS）缺陷症是中国遗传性易栓症患者最为常见的危险因素之一。除了作为活化蛋白C（APC）的辅因子，PS还可作为组织因子途径抑制物（TFPI）的辅因子发挥抗凝功能，但PS突变导致TFPI抗凝作用减弱未见报道。项目组在血栓患者中发现了PS G267E新突变，携带突变患者其抗原及APC辅因子活性均正常，但TFPI辅因子活性减弱。突变位于PS的SHBG结构域，参与同TFPI及FV的结合。我们猜测突变可能通过影响PS与TFPI的结合，或影响PS与FV的结合而削弱TFPI辅因子抗凝作用。本项目拟体外表达突变及不同电荷氨基酸替换蛋白，利用酶动力学及表面等离子共振技术探讨突变对TFPI辅因子活性的影响，明确其致栓机制；制备PS缺陷小鼠并诱导血栓形成，经输注突变蛋白以印证突变在体内的致栓风险，阐明PS突变导致其TFPI辅因子功能缺陷参与血栓形成的新机制，为完善PS缺陷症的临床诊断提出依据。

Congenital Protein S (PS) deficiency is one of the most common risk factors for patients with inherited venous thromboembolism. As an anticoagulant molecule that functions as a cofactor for activated protein C (APC), PS also serves as an efficient synergistic tissue factor pathway inhibitor (TFPI) cofactor in inhibition of FXa, yet mutations on PS leading to dysfunctions of TFPI have not been reported. PS mutation G267E was identified in a thrombotic individual with normal APC cofactor activity and antigen levels, whereas reduced anticoagulant cofactor activity of TFPI was uncovered. As the mutation located in the SHBG domain where mediated the binding of TFPI and FV, we speculated that the mutant would either directly affect bindings of TFPI or alter the binding affinity between PS and FV. To elucidate the pathogenesis of the mutation leading to PS deficiency, we propose in vitro expression of several PS mutants at residue G267, and conduct enzymatic function and surface plasmon resonance to probe the structural changes brought by the mutation. In vivo risk of thrombosis will also be evaluated by animal models via RNA interference of in vivo PS level. The aim of the project is to explore the possible domains of PS engaged in TFPI function, and elucidate the underlying mechanism related to thrombosis, setting foundations for the future improvement on the diagnosis of PS deficiency.