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

 描述(申请人提供)：作为血小板表面第二丰富的膜受体复合体，糖蛋白(GP)Ib-IX-V复合体是血小板生理所必需的。GPIB-IX-V最初被确定为von Willebrand因子(VWF)的受体，因此对止血和血栓形成至关重要，它还被开发为在炎症、癌症转移、血小板生成和清除方面的其他作用。这种多亚单位受体复合体的功能障碍可导致严重的出血素质，并导致许多心血管疾病。然而，目前尚不清楚该复合体如何实现其多方面的功能，甚至其通过与VWF相互作用来感知血管内流体剪应力升高的典型功能。与此相关的是，关于GPIB-IX的另一个基本问题，即复合体中不直接参与与VWF相互作用的Ibü和IX亚基的功能，仍然没有答案。继我们对GPIB-IX-V的结构和四级结构的阐明，特别是我们最近在Iba的茎区发现了一个机械敏感结构域(MSD)后，我们假设VWF结合和拉动Iba亚单位的N-末端结构域会诱导MSD的展开，从而触发附近的Ib和IX胞外域的构象变化。我们建议用多学科方法在3个具体目标上测试这一潜在的范式转换假说。目的1表征IBAMSD的生物物理性质和力诱导的去折叠的功能后果。目的2确定IBAMSD的特征，并检验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Ibü和Ix胞外区的构象变化是否以及如何介导GPIb-Ix的跨膜信号。拟议研究的完成将有助于阐明GPIB-IX-V复合体的关键机械传感机制，解决血液和血流之间的相互作用，为未来研究许多关于GPIB-IX-V的未知现象提供方向，并设计新的治疗策略来治疗相关的出血疾病。

 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.