Peptide Splicing in the Proteasome Creates a Novel Type of Antigen with an Isopeptide Linkage
Peptide Splicing in the Proteasome Creates a Novel Type of Antigen with an Isopeptide Linkage
复制标题
DOI：
10.4049/jimmunol.1402454
复制
发表时间：
2015-11-01
影响因子：
4.4
通讯作者：
Ovaa, Huib
中科院分区：
文献类型：
--
作者：
Berkers, Celia R.;de Jong, Annemieke;Ovaa, Huib
蛋白酶体能够产生剪接的Ag，其中蛋白质的两个远端部分被切除并连接在一起以形成新的肽，用于由MHC I类分子呈递。这些非连续表位是通过蛋白酶体活性位点催化的转肽反应产生的。蛋白酶体中的转肽反应遵循明确的规则，并且当C-末端连接配偶体在连接位点含有赖氨酸或精氨酸残基时特别有效地发生。赖氨酸含有两个氨基，理论上它们都可以参与连接反应，这意味着不仅可以形成肽键，而且可以形成异肽键。使用核磁共振光谱，我们证明在本研究中，蛋白酶体可以使用的N-末端赖氨酸残基的epsilon-氨基基团在转肽反应，以创建一种新型的后修饰的表位。我们发现，与α连接相比，α连接的总体效率仅低10倍，这表明蛋白酶体可以产生足够的异肽Ag来引起T细胞应答。此外，我们表明，异肽对进一步的蛋白酶体加工比正常肽更稳定，我们证明，异肽可以结合HLA-A2.1和HLA-A3具有高亲和力。这些特性可能增加了细胞表面上呈递的ε连接肽的分数，用于CD 8（+）T细胞监视。最后，我们表明，异肽抗原在体内是免疫原性的。我们假设，连接是一个真正的翻译后修饰，这表明蛋白酶体可以创建一个新的类型的银，可能在免疫中发挥作用。
The proteasome is able to create spliced Ags, in which two distant parts of a protein are excised and ligated together to form a novel peptide, for presentation by MHC class I molecules. These noncontiguous epitopes are generated via a transpeptidation reaction catalyzed by the proteasomal active sites. Transpeptidation reactions in the proteasome follow explicit rules and occur particularly efficiently when the C-terminal ligation partner contains a lysine or arginine residue at the site of ligation. Lysine contains two amino groups that theoretically may both participate in ligation reactions, implying that potentially not only peptide but also isopeptide linkages could be formed. Using nuclear magnetic resonance spectroscopy, we demonstrate in the present study that the proteasome can use the epsilon-amino group of an N-terminal lysine residue in transpeptidation reactions to create a novel type of posttranslationally modified epitopes. We show that the overall efficiency of epsilon ligation is only 10-fold lower as compared with alpha ligation, suggesting that the proteasome can produce sufficient isopeptide Ag to evoke a T cell response. Additionally, we show that isopeptides are more stable toward further proteasomal processing than are normal peptides, and we demonstrate that isopeptides can bind to HLA-A2.1 and HLA-A3 with high affinity. These properties likely increase the fraction of epsilon-ligated peptides presented on the cell surface for CD8(+) T cell surveillance. Finally, we show that isopeptide Ags are immunogenic in vivo. We postulate that epsilon ligation is a genuine posttranslational modification, suggesting that the proteasome can create a novel type of Ag that is likely to play a role in immunity.