The Carbohydrate-linked Phosphorylcholine of the Parasitic Nematode Product ES-62 Modulates Complement Activation
The Carbohydrate-linked Phosphorylcholine of the Parasitic Nematode Product ES-62 Modulates Complement Activation
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DOI：
10.1074/jbc.m115.702746
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发表时间：
2016-05-27
影响因子：
4.8
通讯作者：
Raynes, John G.
中科院分区：
文献类型：
--
作者：
Ahmed, Umul Kulthum;Maller, N. Claire;Raynes, John G.
寄生线虫产生各种碳水化合物连接的含磷酰胆碱（PCh）的分子，包括ES-62，一种N-连接聚糖末端被PCh取代的蛋白质。PCh组分在生物学上很重要，因为它是免疫调节作用所必需的。我们发现，大多数ES-62结合到一个单一的蛋白质，C-反应蛋白（CRP），在正常人血清中，显示钙依赖性，高亲和力的相互作用和能力，形成大的复合物。出乎意料的是，与PCh-BSA和含PCh的肺炎链球菌细胞壁多糖相比，CRP与ES-62的结合未能有效地激活补体直到C3转化酶阶段。C1 q捕获试验证明血清中ES-62-CRP-C1 q相互作用。三种配体都以相似的程度激活C1并产生C4 b。然而，在ES-62与CRP结合后没有产生C2 a活性位点，表明C2裂解对于含有ES-62的复合物的效率低得多。我们认为，C2裂解失败是由于碳水化合物结合的PCh的灵活性和减少接近的C1复合物的原因，C2裂解不良。这一点通过使用仅在具有柔性PCh方面与ES-62相似的合成类似物来证实。此外，ES-62显示在CRP相互作用后耗尽早期补体组分，例如限速C4，从而抑制经典途径活化。因此，柔性PCh-聚糖代表了补体激活颠覆的新机制。这些数据说明了补体活化的限速C4/C2阶段的重要性，并揭示了ES-62免疫调节机制的新补充，具有可能的治疗应用。
Parasitic nematodes manufacture various carbohydrate-linked phosphorylcholine (PCh)-containing molecules, including ES-62, a protein with an N-linked glycan terminally substituted with PCh. The PCh component is biologically important because it is required for immunomodulatory effects. We showed that most ES-62 was bound to a single protein, C-reactive protein (CRP), in normal human serum, displaying a calcium-dependent, high-avidity interaction and ability to form large complexes. Unexpectedly, CRP binding to ES-62 failed to efficiently activate complement as far as the C3 convertase stage in comparison with PCh-BSA and PCh-containing Streptococcus pneumoniae cell wall polysaccharide. C1q capture assays demonstrated an ES-62-CRP-C1q interaction in serum. The three ligands all activated C1 and generated C4b to similar extents. However, a C2a active site was not generated following ES-62 binding to CRP, demonstrating that C2 cleavage was far less efficient for ES-62-containing complexes. Weproposed that failure of C2 cleavage was due to the flexible nature of carbohydrate-bound PCh and that reduced proximity of the C1 complex was the reason that C2 was poorly cleaved. This was confirmed using synthetic analogues that were similar to ES-62 only in respect of having a flexible PCh. Furthermore, ES-62 was shown to deplete early complement components, such as the rate-limiting C4, following CRP interaction and thereby inhibit classical pathway activation. Thus, flexible PCh-glycan represents a novel mechanism for subversion of complement activation. These data illustrate the importance of the rate-limiting C4/C2 stage of complement activation and reveal a new addition to the repertoire of ES-62 immunomodulatory mechanisms with possible therapeutic applications.