Alpha-macroglobulin from Limulus polyphemus exhibits proteinase inhibitory activity and participates in a hemolytic system.
Alpha-macroglobulin from Limulus polyphemus exhibits proteinase inhibitory activity and participates in a hemolytic system.
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DOI：
10.1021/bi00495a009
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发表时间：
1990-10
期刊：
影响因子：
2.9
通讯作者：
J. Enghild;I. Thøgersen;Guy S. Salvesen;Georg H. Fey;N. Figler;S. Gonias;Salvatore V. Pizzo
中科院分区：
文献类型：
--
作者：
J. Enghild;I. Thøgersen;Guy S. Salvesen;Georg H. Fey;N. Figler;S. Gonias;Salvatore V. Pizzo
蛋白酶抑制剂的α-巨球蛋白家族与补体成分C3、C4和C5之间的显著一级序列同源性意味着这些蛋白质来自共同的祖先。来自古老无脊椎动物鲎的血淋巴含有补体样和蛋白酶抑制活性。在这份报告中，我们提出的证据，L。Polyphemus α-巨球蛋白不仅具有蛋白酶抑制活性，而且还参与鲎的溶解系统。该蛋白是分子量为185 kDa的亚基的二硫键连接的二聚体。L. polyphemus α-巨球蛋白经历了主要的构象变化，没有检测到蛋白酶相关的多聚化。L. polyphemus α-巨球蛋白是唯一可检测到的L.血淋巴蛋白酶抑制遵循大多数α-巨球蛋白共有的一般“捕获”机制;然而，尽管存在功能性硫酯，但未检测到蛋白酶与抑制剂的共价连接。此外，该抑制剂表现出硫酯介导的与绵羊红细胞的结合，这也是在补体成分如C3中观察到的特性。用甲胺处理血淋巴以消耗功能蛋白，破坏血淋巴的蛋白酶抑制能力和溶解活性。这两种活动恢复通过添加纯化的蛋白质耗尽血淋巴。用纯化的L. Polyphemus α-巨球蛋白的研究表明，硫酯结合了甘油以及甲胺，这是人C3共有的性质。数据支持L. Polyphemus α-巨球蛋白既是蛋白酶抑制剂，又是溶解系统的一部分，在α-巨球蛋白家族的两个不同侧面之间提供联系。由于这两种特性都包含在一个分子中，我们建议命名为“limac”来描述这种鲎α-巨球蛋白补体样蛋白。
Significant primary sequence homology between the alpha-macroglobulin family of proteinase inhibitors and the complement components C3, C4, and C5 implies that these proteins arose from a common ancestor. Hemolymph from the ancient invertebrate Limulus polyphemus contains both complement-like and proteinase inhibitory activity. In this report, we present evidence that L. polyphemus alpha-macroglobulin not only possesses proteinase inhibitory activity, but it also participates in the lytic system of the horseshoe crab. The protein is a disulfide-linked dimer of subunits of molecular mass 185 kDa. Upon reaction with proteinase or methylamine, L. polyphemus alpha-macroglobulin underwent a major conformational change and no proteinase-associated multimerization was detected. L. polyphemus alpha-macroglobulin is the only detectable inhibitor of a number of proteinases in L. polyphemus hemolymph. Proteinase inhibition follows the general "trapping" mechanism shared by most alpha-macroglobulins; however, no covalent linking of proteinases to the inhibitor was detected despite the presence of a functional thiolester. Moreover, the inhibitor demonstrated thiolester-mediated binding to sheep erythrocytes, a property also observed with complement components such as C3. Depletion of functional protein by treatment of hemolymph with methylamine destroyed the proteinase inhibitory capacity and the lytic activity of the hemolymph. Both activities were restored by adding purified protein to depleted hemolymph. Studies with purified L. polyphemus alpha-macroglobulin demonstrated that the thiolester incorporates glycerol as well as methylamine, a property shared by human C3. The data support the hypothesis that L. polyphemus alpha-macroglobulin is both a proteinase inhibitor and part of a lytic system, providing a link between the two distinct sides of the alpha-macroglobulin family. Because both properties are contained in one molecule, we propose the name "limac" to describe this Limulus alpha-macroglobulin complement-like protein.