STRUCTURE AND FUNCTION OF THROMBOSPONDIN

凝血酶原蛋白(TSP)是一种由3个二硫键连接的450 kDa蛋白质 锁链。它由血小板和某些培养细胞分泌。它 与细胞和许多不同的蛋白质结合；它可能作为一种 粘附性或亚细胞基质蛋白。我们观察到， TSP I)具有构象敏感的硫醇，II)具有链内 具有构象依赖稳定性的二硫键，以及iii) 容易与其他蛋白质形成二硫键连接的络合物，并 与TSP的其他分子结合。我假设这反映了一种 TSP作为共价交联蛋白的动态功能。作为一名 对这一假设的检验和对TSP的进一步表征， 硫醇的数目和位置与构象敏感 二硫键将被确定，并对蛋白质的特异性 以及用于硫醇-二硫键交换的二硫键的位置 将会被检查。硫醇-二硫键交换被证明具有 最适pH值低于7(预计为8-10)；这将是 研究以确定pH依赖是否反映了pH- 依赖的构象变化或另一种构象的影响 硫醇解离上的电离基团。最后，尝试 将确定硫醇是否是TSP所必需的 与细胞(包括血小板)的结合、其凝集素活性或 血小板聚集。

Thrombospondin (Tsp) is a 450 kDa protein with 3 disulfide-linked chains. It is secreted by platelets and certain cultured cells. It binds to cells and many different proteins; it may function as an adhesive or sub-cellular matrix protein. We have observed that Tsp i) has a conformation-sensitive thiol, ii) has an intrachain disulfide bond with a conformation-dependent stability, and iii) readily forms disulfide-linked complexes with other proteins and with other molecules of Tsp. I hypothesize that this reflects a dynamic function of Tsp as a covalent crosslinking protein. As a test of this hypothesis and for further characterization of Tsp, the number and locations of thiols and conformation-sensitive disulfide bonds will be determined, and the specificity for protein and for location of disulfide bonds for the thiol-disulfide exchange will be examined. The thiol-disulfide exchange was shown to have a pH optimum below 7 (8-10 would be predicted); this will be studied to determine if the pH dependence reflects a pH- dependent conformational change or the influence of another ionizable group on the dissociation of the thiol. Finally, attempts will be made to determine whether the thiol is necessary for Tsp binding to cells (including platelets), for its lectin activity or for platelet aggregation.