Structure-Function Study of Angiogenic Protein,Ephrin B2

ephrin是膜结合蛋白，作为受体酪氨酸激酶的Eph家族的配体。ephrin和Eph受体参与血管生成、轴突引导和地形图的形成和分割。有证据表明，ephrin B2及其受体Eph B4分别是区分动脉和静脉的第一个分子标记，这些分子参与了血管形成所建立的初级毛细血管网络的血管新生重塑的最早阶段。我们的长期目标是利用x射线晶体学获得ephrin和Eph受体功能的结构基础。这些信息对于理解血管生成的原理和相关疾病如癌症、眼病和缺血是至关重要的。目前对ephrin和Eph受体的研究主要集中在两个关键问题上：1)ephrin胞外结构域如何聚集激活Eph受体。2)体外观察到的Eph受体和ephrin结合混杂的基础是什么，这表明体内一定存在一系列特异性。为了解决这些问题，我们提出解决ephrin B2胞外结构域的X射线晶体结构，对此我们已经获得了衍射良好的晶体。我们期望确定配体寡聚化的性质，并了解配体如何与ephh受体结合。ephrin B2的高分辨率、三维结构将使我们能够设计单克隆抗体的表位，并允许未来的定向药物设计，这两者都可能具有治疗应用。此外，我们建议通过结晶和求解ephrin-Eph配体结合域复合物的x射线晶体结构来解决ephrin- ephrin结合的结构基础。最后，我们建议通过晶体学研究整个Eph受体外结构域的结构与功能之间的关系，以确定非配体结合结构域的功能。

The ephrins are membrane-bound proteins that act as ligands for the Eph Family of receptor tyrosine kinases. Ephrins and Eph receptors are involved in angiogenesis, axon guidance and topographic map formation, and segmentation. Evidence suggest that ephrin B2 and its receptor Eph B4, are the first molecular markers that distinguish arteries from veins, respectively, and these molecules are involved in the earliest stages of angiogenic remodeling of the primary capillary network established by vasculogenesis. Our long term objective is to obtain the structural basis for the function of the ephrins and the Eph receptors using X-ray crystallography. This information is critical for understanding the principles of angiogenesis and the relevant diseases such as cancer, eye diseases, and ischemia. Current studies on ephrins and Eph receptors focus on two key questions: 1) How ephrin extracellular domains cluster to activate Eph receptors. 2) What is the basis of the promiscuity of binding between Eph receptors and ephrins that is observed in vitro, which suggest a range of specificity that must be present in vivo. To address theses problems we propose to solve the X- ray crystal structure of ephrin B2 extracellular domain, for which we have already obtained well-diffracting crystals. We expect to determine the nature of ligand oligomerization, and see how the ligand might be bound by Eph receptors. The high- resolution, three-dimensional structure of ephrin B2 will allow us to design epitopes for monoclonal antibodies, and allow future directed-drug design, both of which could have therapeutic applications. Further, we propose to address the structural basis for Eph-ephrin binding by crystallizing and solving X-ray crystal structures of complexes of ephrin-Eph ligand binding domains. Finally, we propose to investigate the relationship between structure and function of the entire Eph receptor ectodomains via crystallography, to ascertain the function of the non-ligand binding domains.