An amphioxus RAG1-like DNA fragment encodes a functional central domain of vertebrate core RAG1
An amphioxus RAG1-like DNA fragment encodes a functional central domain of vertebrate core RAG1
复制标题
DOI：
10.1073/pnas.1318843111
复制
发表时间：
2014-01-07
影响因子：
11.1
通讯作者：
Liu, Xiaolong
中科院分区：
文献类型：
--
作者：
Zhang, Yanni;Xu, Ke;Liu, Xiaolong
脊椎动物免疫系统中高度多样化的抗原受体库是通过重组激活基因（RAG）RAG 1和RAG 2编码的蛋白质通过称为可变、多样性和连接[V（D）J]基因重组的过程产生的。基于对脊椎动物RAG蛋白的研究，人们对RAG的起源和进化提出了许多假说。这个问题仍然没有得到解决，在我们对适应性免疫进化的理解中留下了巨大的空白。在这里，我们表明，文昌鱼基因组包含一个古老的RAG 1样的DNA片段（bfRAG 1 L），编码的病毒相关蛋白，比脊椎动物RAG 1短得多，并拥有一个区域同源的核心RAG 1（cRAG 1）的中央结构域。bfRAG 1 L还含有意想不到的逆转录病毒II型核酸酶活性位点基序DXN（D/E）XK，并且能够降解DNA和RNA。此外，bfRAG 1 L与cRAG 1的中心结构域具有重要的功能特性，包括与RAG 2的相互作用和定位于细胞核。值得注意的是，将bfRAG 1 L重构为cRAG 1样蛋白产生了能够识别重组信号序列并在小鼠RAG 2存在下进行V（D）J重组的酶。此外，这种重组的cRAG 1样蛋白可以介导RAG 1缺陷小鼠中抗原受体基因的组装。总之，我们的研究结果表明，文昌鱼bfRAG 1 L编码的蛋白质是功能上等同于cRAG 1的中央结构域，并为进一步进化介导V（D）J重组做好了充分的准备。因此，我们的研究结果为RAG 1的进化起源提供了独特的见解。
The highly diversified repertoire of antigen receptors in the vertebrate immune system is generated via proteins encoded by the recombination activating genes (RAGs) RAG1 and RAG2 by a process known as variable, diversity, and joining [V(D)J] gene recombination. Based on the study of vertebrate RAG proteins, many hypotheses have been proposed regarding the origin and evolution of RAG. This issue remains unresolved, leaving a significant gap in our understanding of the evolution of adaptive immunity. Here, we show that the amphioxus genome contains an ancient RAG1-like DNA fragment (bfRAG1L) that encodes a virus-related protein that is much shorter than vertebrate RAG1 and harbors a region homologous to the central domain of core RAG1 (cRAG1). bfRAG1L also contains an unexpected retroviral type II nuclease active site motif, DXN(D/E)XK, and is capable of degrading both DNA and RNA. Moreover, bfRAG1L shares important functional properties with the central domain of cRAG1, including interaction with RAG2 and localization to the nucleus. Remarkably, the reconstitution of bfRAG1L into a cRAG1-like protein yielded an enzyme capable of recognizing recombination signal sequences and performing V(D)J recombination in the presence of mouse RAG2. Moreover, this reconstituted cRAG1-like protein could mediate the assembly of antigen receptor genes in RAG1-deficient mice. Together, our results demonstrate that amphioxus bfRAG1L encodes a protein that is functionally equivalent to the central domain of cRAG1 and is well prepared for further evolution to mediate V(D)J recombination. Thus, our findings provide unique insights into the evolutionary origin of RAG1.