STRUCTURE AND FUNCTION OF THROMBOSPONDIN

血小板反应蛋白（Tsp）是一种450 kDa的蛋白质，具有3个二硫键连接的 店 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;它可能起着 粘附或亚细胞基质蛋白。 我们观察到 Tsp i）具有构象敏感的巯基，ii）具有链内 具有构象依赖性稳定性的二硫键，和iii） 容易与其他蛋白质形成二硫键连接的复合物， 与其他的TSP分子结合。 我假设这反映了 Tsp作为共价交联蛋白的动态功能。 作为 为了验证这一假设并进一步表征Tsp， 巯基的数量和位置以及构象敏感性 将测定二硫键，并测定对蛋白质的特异性 以及用于巯基-二硫键交换的二硫键的位置 将被审查。 巯基-二硫键交换被证明具有 最佳pH值低于7（预计为8-10）;这将是 研究以确定pH依赖性是否反映pH- 依赖的构象变化或另一个的影响 可电离基团对硫醇的解离的影响。 最后，尝试 将作出决定是否硫醇是必要的Tsp 结合细胞（包括血小板），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.