STRUCTURE AND FUNCTION OF PLATELET GPIIB/IIIA

血小板GPIIb/IIIa复合物是几种 粘附糖蛋白，并已被发现是一种原型 Arg-Gly-Asp（RGD）特异性粘附家族成员 受体。 对其他成员的了解相对较少。 但很明显，它们在分子水平上不同， 重量、细胞分布和含RGD的特异性 配体，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），存在于广泛的 包括血小板在内的各种细胞，我们已经证明， 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粘附受体家族。 利用办法 与我们用于研究GPIIb/IIIa的方法类似，我们的目标是使用 我们在VLA抗原研究中的经验，以确定其 结构和功能作用，并确定如何 该功能与血小板GPIIb/IIIa的功能有关。 我们对GPIIb/IIIa的研究集中在阐明 GPIIb/IIIa的配体结合活性的机制是 监管. 我们的研究表明，血小板含有大量的 GPIIb/IIIa池，可能位于连接的表面内 小管系统（SCCS），而在静息血小板中， SCCS可以被一些但不是所有的细胞外蛋白质进入。 该隔室可能不与细胞外粘合剂相互作用 糖蛋白，直到可及性限制被克服， 血小板活化 我们将测试这一假设利用 免疫化学和电子显微镜技术。 如果这 模型得到支持，我们将进一步研究 规范SCCS的可访问性，并确定其作用 在配体结合中的隔室。 如果这个假设被证实 不正确的，我们将测试替代模型，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，a 大IgM单克隆抗体，其仅结合GPIIb/IIIa， 激活血小板 我们还将确定 不同单克隆抗体定义的亚区之间 GPIIb/IIIa分子在血小板活化后发生变化。 利用类似的方法，我们将确定 调节配体结合活性的机制 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.