Alpha-2-Macroglobulin of Invertebrates

α -2巨球蛋白是存在于所有脊椎动物的血浆蛋白，具有广谱蛋白酶抑制剂的功能。本研究将研究马蹄蟹(Limulus polyphemus) α -2巨球蛋白的结构和功能。本实验室已获得了大量的鲎α -2巨球蛋白的肽序列信息和抗血清，将用于从一个cDNA文库中分离和测序鲎变形细胞的poly (a)+ RNA。与拥有大量血浆蛋白酶抑制剂的脊椎动物不同，鲎的血浆中α -2-巨球蛋白是唯一的蛋白酶抑制剂，这有助于其在体内的功能表征。拟议的研究将探讨α -2巨球蛋白参与受体介导的蛋白酶清除途径的可能性。α -2巨球蛋白也参与鲎血浆中的细胞溶解系统，该系统可能与脊椎动物的补体系统相似。将对该系统进行表征，鉴定参与分子，并对其作用顺序和细胞溶解机制进行表征。这项研究首次对无脊椎动物的补体样细胞溶解系统进行了分子表征，将为这一重要的免疫样防御系统提供有价值的信息。多细胞生物有各种各样的防御策略来限制它们对潜在病原体的易感性。这些防御机制通常涉及血液中的细胞和可溶性因子。这些血液因子中最古老的一种是血浆蛋白，α -2巨球蛋白。这种分子存在于从无脊椎动物到人类的许多动物体内。α -2巨球蛋白似乎有两种一般的功能，一种是作为血液或细胞表面的酶的陷阱，否则它们可能会因消化其他蛋白质而造成损害，第二种是作为特定生化连锁反应的一部分，其功能是杀死入侵的病原体或外来细胞。本研究的目的是表征马蹄蟹-2巨球蛋白的结构和功能，鲎是一种相对原始的动物。这项研究的结果将有助于理解自然界中发现的各种防御机制，也可能揭示高等生物防御分子的功能。

The alpha-2-macroglobulins are plasma proteins that are present in all classes of vertebrates and that function as broad-spectrum protease inhibitors. The proposed research will investigate the structure and function of a form of alpha-2-macroglobulin from the horseshoe crab, Limulus polyphemus. This laboratory has obtained extensive peptide sequence information and antisera to Limulus alpha-2-macroglobulin which will be used to isolate and sequence the full length cDNA from a CDNA library developed to the poly (A)+ RNA of the Limulus amebocyte. In contrast to vertebrates, which possess a large number of plasma protease inhibitors, alpha-2- macroglobulin is the only protease inhibitor in the plasma of Limulus, which should facilitate its functional characterization in vivo. The proposed research will investigate the possibility that alpha-2-macroglobulin participates in a receptor-mediated clearance pathway for proteases. Alpha-2-macroglobulin also participates in a cytolytic system in the plasma of Limulus that may be homologous to the vertebrate complement system. This system will be characterized, the participating molecules identified, and their sequence of action and mechanism of cytolysis characterized. This study, which represents the first molecular characterization of a complement-like cytolytic system in an invertebrate, should yield valuable information concerning this important immune-like defense system. %%% Multicellular organisms have a varied array of defense strategies that limit their susceptibility to damage by potential pathogens. These defense mechanisms generally involve cells and soluble factors of the blood. One of the most ancient of these blood factors is the plasma protein, alpha-2-macroglobulin. This molecule is found in a wide range of animals from invertebrates to humans. Alpha-2-macroglobulin appears to have two general types of function, one as a trap for enzymes in the blood or on cell surfaces that might otherwise do damage by digesting other proteins, and the second is as a part of a specific biochemical chain reaction that functions to kill invading pathogens or foreign cells. The purpose of this research is to characterize the structure and function of the alpha-2-macroglobulin from the horseshoe crab, Limulus, a relatively primitive animal. The results of this research will contribute to understanding of the diverse array of defense mechanisms found in nature, and may also shed light on the functioning of the defense molecules of higher organisms.