Regulation of von Willebrand factor processing

描述(申请人提供)：von Willebrand因子是血浆中的一种多聚体蛋白，通过调节血管损伤部位的血小板黏附在初级止血中发挥重要作用。血管性血友病因子的止血作用依赖于其亚基的多聚化程度。血管内皮细胞和血小板分泌的一部分von Willebrand因子含有一种高度聚合的von Willebrand因子，它可以自发地凝集血小板，在循环中形成病理性闭塞血栓。这些高度聚合的von Willebrand因子被血浆中的金属蛋白酶ADAMTS13以剪切依赖的方式蛋白质降解为较少聚合的形式。因此，血浆中von Willebrand因子的分泌后处理是调节von Willebrand因子功能的关键步骤。虽然剪切力和ADAMTS13的存在对加工是必不可少的，但这一过程是如何调节的尚不清楚。本申请中提出的研究将集中在von Willebrand因子亚单位内各结构域之间的分子内相互作用，以及von Willebrand因子与其他大分子(包括辅因子)之间的分子间相互作用，如何调节ADAMTS13对von Willebrand因子的蛋白质降解过程。在目标1中，我们将利用von Willebrand因子的重组和突变片段，确定瑞斯托菌素结合位点在调节A2结构域可被ADAMTS13切割的过程中的作用。在目标2中，我们将研究von Willebrand因子亚基中三个‘A’结构域之间的变构相互作用以及它们与其他大分子的相互作用如何调节切割位点的暴露和可及性。在目标3中，我们将描述肝素和肝素样辅因子如何通过ADAMTS13调节von Willebrand因子的切割。对这一过程的进一步了解将为预防和治疗由von Willebrand因子异常、不足或过度加工引起的血栓性和出血性疾病提供新的策略。 与公共健康相关：拟议的研究重点是了解血浆金属蛋白酶如何调节黏附蛋白von Willebrand因子的功能，该黏附蛋白可在血管损伤部位启动血小板黏附和聚集。这些研究将进一步加深我们对金属蛋白酶和一种新发现的辅因子如何在健康和疾病中调节von Willebrand因子的功能和血栓形成的理解。

DESCRIPTION (provided by applicant): Von Willebrand factor is a multimeric protein in plasma that plays an essential role in primary hemostasis by mediating platelet adhesion at sites of vascular injury. The hemostatic function of von Willebrand factor depends on the degree of multimerization of its subunits. A fraction of the von Willebrand factor secreted from endothelial cells and platelets contains a highly polymerized form of von Willebrand factor that would spontaneously agglutinate platelets to form pathological occlusive thrombi in the circulation. These highly polymerized forms of von Willebrand factor are proteolytically processed to a less polymerized form in a shear-dependent manner by the metalloprotease ADAMTS13 in plasma. Thus, post-secretion processing of von Willebrand factor in plasma is a critical step in regulating the function of von Willebrand factor. Although shear stress and the presence of ADAMTS13 are essential for processing, how this process is regulated is not known. Studies proposed in this application will focus on how intramolecular interactions among the various domains within the von Willebrand factor subunit, and intermolecular interactions between von Willebrand factor and other macromolecules, including that of a cofactor, regulate the proteolytic processing of von Willebrand factor by ADAMTS13. In aim 1, by use of recombinant and mutant fragments of von Willebrand factor, we will determine the role of the ristocetin binding site in regulating the accessibility of the A2 domain for cleavage by ADAMTS13. In aim 2, we will study how allosteric interactions among the three 'A' domains within the von Willebrand factor subunit and their interactions with other macromolecules modulate the exposure and accessibility of the cleavage site. In aim 3, we will characterize how heparin and a heparin-like cofactor regulate the cleavage of von Willebrand factor by ADAMTS13. An improved understanding of this process would lead to new strategies for the prevention and treatment of thrombotic and bleeding diseases caused by aberrant, inadequate or excessive processing of von Willebrand factor. PUBLIC HEALTH RELEVANCE: The proposed research is focused on understanding how a plasma metalloprotease regulates the function of the adhesive protein von Willebrand factor, which initiates platelet adhesion and aggregation at the site of vascular injury. These studies will further our understanding of how the metalloprotease and a newly identified cofactor regulate the function of von Willebrand factor and thrombi formation in health and in disease.