STRUCTURE AND FUNCTION OF PLATELET GPIIB/IIIA

血小板GPIIb/IIIa复合体是多种分子的受体 粘附性糖蛋白，已被发现是一种原型 精氨酸-甘氨酸-天冬氨酸(RGD)特异性黏附家族成员 感受器。对其他成员的了解相对较少 但很明显，它们在分子上是不同的 含有RGD的重量、细胞分布和特异性 配基，所有这些都可能是功能差异的基础。 两年来，我们一直在研究一组细胞表面 糖蛋白(VLA抗原)广泛存在于 各种细胞，包括血小板，我们已经在那里展示了它们 与血小板GPI/a、GPI/c和GPII/a相同。非常 最近发现，这些VLA抗原是 RGD-黏附受体家族。利用途径 与我们用来研究GPIIb/IIIa的那些类似，我们的目标是使用 我们在VLA抗原研究中的经验 在血小板上的结构和功能作用，并确定如何 这一功能与血小板GPIIb/IIIa的功能有关。 我们对GPIIb/IIIa的研究主要集中在阐明 GPIIb/IIIa配体结合活性的机制 受监管的。我们的研究表明，血小板中含有大量的 GPIIb/IIIa池，可能位于连接的表面内 小管系统(SCCS)，以及静息状态下的血小板 SCCS可以被一些但不是所有的细胞外蛋白进入。 这个隔室可能不会与细胞外粘合剂相互作用 糖蛋白，直到可获得性限制被克服 血小板被激活。我们将使用以下工具验证这一假设 免疫化学和电子显微镜技术。如果这个 模型得到支持，我们将进一步研究 规范SCCS的可访问性并确定这一点的作用 配基结合中的隔间。如果这一假设得到证实 不正确，我们将测试其他模型，这些模型提出 GPIIb/IIIa-配体结合活性的诱导是由于 微环境或构象变化。这将是 通过研究PAC-1片段的结合活性，a 仅与GPIIb/IIIa结合的大分子IgM单抗 激活的血小板。我们还将确定距离是否 在不同的单抗定义的亚区之间 血小板活化后，GPIIb/IIIa分子发生变化。 使用类似的方法，然后我们将确定 其配体结合活性的调控机制 血小板VLA抗原。

The platelet GPIIb/IIIa complex is a receptor for several adhesive glycoproteins and has been found to be a prototypic member of a family of Arg-Gly-Asp (RGD)-specific adhesion receptors. Relatively little is known of the other members of this family but it is apparent that they differ in molecular weight, cell distribution, and specificity for RGD-containing ligands, all of which probably underlie functional differences. For two years, we have been investigating a set of cell surface glycoproteins (the VLA antigens) which are present on a wide variety of cells including platelets, where we have shown they are identical with platelet GPI/a, GPI/c, and GPII/a. Very recently, it was found that these VLA antigens are a member of the family of RGD-adhesion receptors. Utilizing approaches similar to those we have used to study GPIIb/IIIa, we aim to use our experience in the study of VLA antigens to determine their structure and functional role on platelets, and determine how this function is related to that of platelet GPIIb/IIIa. Our studies of GPIIb/IIIa have focused on elucidation of the mechanism by which the ligand-binding activity of GPIIb/IIIa is regulated. Our studies suggest that platelets contain a large pool of GPIIb/IIIa, perhaps located within the surface connected canalicular system (SCCS), and that in resting platelets the SCCS can be entered by some but not all extra cellular proteins. This compartment may not interact with extracellular adhesive glycoproteins until accessibility constraints are overcome by platelet activation. We will test this hypothesis utilizing immunochemical and electron microscopic techniques. If this model is supported, we will further study the mechanisms which regulate accessibility to the SCCS and determine the role of this compartment in ligand binding. If this hypothesis is proven incorrect, we will test alternative models which propose that the induction of GPIIb/IIIa-ligand binding activity is due to either microenvironmental or conformational changes. This will be done by studying the binding activity of fragments of PAC-1, a large IgM monoclonal antibody which binds to GPIIb/IIIa only on activated platelets. We will also determine if the distances between different monoclonal antibody-defined subregions of GPIIb/IIIa molecules change subsequent to platelet activation. Utilizing similar approaches, we will then determine the mechanisms which regulate the ligand-binding activity of platelet VLA-antigens.