Enhanced recognition of plasma proteins in a non-native state by complement C3b. A possible clearance mechanism for damaged proteins in blood.
Enhanced recognition of plasma proteins in a non-native state by complement C3b. A possible clearance mechanism for damaged proteins in blood.
复制标题
补体 C3b 增强对非天然状态血浆蛋白的识别。
DOI：
10.1016/j.molimm.2014.10.022
复制
发表时间：
2015
影响因子：
3.6
通讯作者：
Kew,RichardR
中科院分区：
文献类型：
--
作者：
Ramadass,Mahalakshmi;Ghebrehiwet,Berhane;Kew,RichardR
补体C3是免疫系统的关键液相蛋白，其共价标记致病细胞和分子以用于随后的清除。以前，我们报告说，补体激活的结果在血清中形成多个C3 b：血浆蛋白复合物。然而，尚不清楚C3 b是否与任何血浆蛋白紧密结合或优先结合受损蛋白。本研究的目的是确定C3 b是否在非天然状态下与血浆蛋白偶联，以及这是否可能是检测和清除血液中受损蛋白的潜在机制。使用具有旁路途径蛋白质C3、因子B和D的纯化的体外系统，观察到三种纯化的血浆蛋白（白蛋白、α-1蛋白酶抑制剂、维生素D结合蛋白）的盐酸胍变性大大增加了它们与C3 B形成共价复合物的能力。然而，天然维生素D结合蛋白，共价连接到C3 b，仍然保留了结合其天然配体G-肌动蛋白的能力，表明C3 b连接到血浆蛋白在其天然配置，但变性大大增加了这种相互作用。血清补体激活产生了大量的C3 b：血浆蛋白复合物，结合红细胞膜，表明CR 1介导的清除机制。热变性（60 °C）血清在加入新鲜血清时激活旁路途径，如因子B裂解和iC 3 B产生所证明的，但是这种热处理的血清不能产生促炎肽C5 a。这些结果表明，C3识别并标记受损的血浆蛋白，以便随后从血液中去除，而不会触发促炎功能。
Complement C3 is a key fluid-phase protein of the immune system that covalently tags pathogenic cells and molecules for subsequent clearance. Previously, we reported that complement activation results in the formation of multiple C3b:plasma protein complexes in serum. However, it is not known if C3b attaches to any plasma protein in close proximity or preferentially binds damaged proteins. The objective of this study was to determine if C3b couples to plasma proteins in a non-native state and if this could be a potential mechanism to detect and clear damaged proteins from the blood. Using a purified in vitro system with alternative pathway proteins C3, factors B and D it was observed that guanidinium-HCl denaturation of three purified plasma proteins (albumin, alpha-1 proteinase inhibitor, vitamin D binding protein) greatly increased their capacity to form covalent complexes with C3b. However, native vitamin D binding protein, covalently attached to C3b, still retained the ability to bind its natural ligand G-actin, indicating that C3b links to plasma proteins in their native configuration but denaturation substantially increases this interaction. Serum complement activation generated a large number of C3b:plasma protein complexes that bound red blood cell membranes, suggesting a CR1-mediated clearance mechanism. Thermally denatured (60 °C) serum activated the alternative pathway when added to fresh serum as evidenced by factor B cleavage and iC3b generation, but this heat-treated serum could not generate the pro-inflammatory peptide C5a. These results show that C3 recognizes and tags damaged plasma proteins for subsequent removal from the blood without triggering proinflammatory functions.