Structure and Function of Platelet Glycoprotein Ib-IX-V Complex

 描述（由申请人提供）：作为血小板表面上第二丰富的膜受体复合物，糖蛋白（GP）Ib-IX-V复合物对血小板生理学至关重要。GPIb-IX-V最初被鉴定为血管性血友病因子（vonWillebrand factor，VWF）的受体，因此对止血和血栓形成至关重要，GPIb-IX-V还在炎症、癌症转移、血小板生成和清除中发挥额外的作用。这种多亚基受体复合物的功能障碍可导致严重的出血素质，并有助于许多心血管疾病。然而，目前尚不清楚该复合物如何执行其多方面的功能，甚至其通过与VWF的相互作用来感测血管中升高的流体剪切应力的典型功能。与此相关，另一个关于GPIb-IX的基本问题，即复合物中IbIbIb 2和IX亚基的功能，它们不直接参与与VWF的相互作用，仍然没有答案。在我们阐明GPIb-IX-V的结构和四级组织之后，特别是我们最近在Iba的茎区中鉴定了一个质膜机械敏感结构域（MSD），我们假设VWF结合并拉动Iba亚基的N-末端结构域诱导MSD展开，这引发附近的IbIbIbis和IX胞外结构域的构象变化。我们建议在3个具体目标中采用多学科方法来测试这一潜在的范式转移假设。目的1是表征力诱导的Iba MSD去折叠的生物物理性质和功能后果。目的2是表征Iba MSD并测试其内在不稳定性是否是Bernard-Soulier综合征发病机制的基础。目的3是确定Ibb-IX和IX胞外结构域的构象变化是否以及如何介导GPIb-IX的跨膜信号传导。这些研究的完成将有助于阐明GPIb-IX-V复合物的关键机械感知机制，解决血液和流量之间的相互作用，为未来研究GPIb-IX-V的许多无法解释的现象提供方向，并设计新的治疗策略来治疗相关的出血性疾病。

 DESCRIPTION (provided by applicant): As the second most abundant membrane receptor complex on the platelet surface, the glycoprotein (GP)Ib-IX-V complex is essential to platelet physiology. Initially identified as the receptor for von Willebrand factor (VWF) and thus critical o hemostasis and thrombosis, GPIb-IX-V is also tapped for additional roles in inflammation, cancer metastasis, platelet genesis and clearance. Malfunction of this multi-subunit receptor complex can lead to severe bleeding diathesis and contribute to many cardiovascular diseases. However, it is not clear how this complex carries out its multi-faceted functions, even its canonical function to sense the elevated fluid shear stress in the blood vessel through its interaction with VWF. Relatedly, another fundamental question about GPIb-IX, the functions of Ibß and IX subunits in the complex that do not directly participate in the interaction with VWF, has remained unanswered. Following up on our elucidation of the structure and quaternary organization of GPIb-IX-V, particularly our recent identification of a juxtamembrane mechano-sensitive structural domain (MSD) in the stalk region of Iba, we hypothesize that VWF binding and pulling on the N-terminal domain of Iba subunit induces unfolding of the MSD, which triggers a conformational change in the nearby Ibß and IX extracellular domains. We propose to test this potentially paradigm-shifting hypothesis with a multidisciplinary approach in 3 specific aims. Aim 1 is characterize the biophysical nature and the functional consequence of force-induced unfolding of the Iba MSD. Aim 2 is to characterize the Iba MSD and test whether its intrinsic instability underlies the pathogenesis of Bernard-Soulier syndrome. Aim 3 is to determine whether and how a conformational change in the Ibß and IX extracellular domains mediates transmembrane signaling of GPIb-IX. Completion of the proposed studies will help to elucidate the critical mechanosensing mechanism by the GPIb-IX-V complex, address the interplay between blood and flow, provide direction for future investigation of many unexplained phenomena about GPIb-IX-V, and devise novel therapeutic strategies to treat related bleeding diseases.