Department of Immunobiology, Yale School of Medicine, New Haven, CT, USA.
Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT, USA.
Nature. 2019 Nov;575(7783):540-544. doi: 10.1038/s41586-019-1753-7. Epub 2019 Nov 13.
Transposons have had a pivotal role in genome evolution and are believed to be the evolutionary progenitors of the RAG1-RAG2 recombinase, an essential component of the adaptive immune system in jawed vertebrates. Here we report one crystal structure and five cryo-electron microscopy structures of Transib, a RAG1-like transposase from Helicoverpa zea, that capture the entire transposition process from the apo enzyme to the terminal strand transfer complex with transposon ends covalently joined to target DNA, at resolutions of 3.0-4.6 Å. These structures reveal a butterfly-shaped complex that undergoes two cycles of marked conformational changes in which the 'wings' of the transposase unfurl to bind substrate DNA, close to execute cleavage, open to release the flanking DNA and close again to capture and attack target DNA. Transib possesses unique structural elements that compensate for the absence of a RAG2 partner, including a loop that interacts with the transposition target site and an accordion-like C-terminal tail that elongates and contracts to help to control the opening and closing of the enzyme and assembly of the active site. Our findings reveal the detailed reaction pathway of a eukaryotic cut-and-paste transposase and illuminate some of the earliest steps in the evolution of the RAG recombinase.
转座子在基因组进化中发挥了关键作用，被认为是 RAG1-RAG2 重组酶的进化祖先，RAG1-RAG2 重组酶是有颌脊椎动物适应性免疫系统的重要组成部分。在这里，我们报告了一个来自棉铃虫的 RAG1 样转座酶 Transib 的一个晶体结构和五个冷冻电镜结构，这些结构捕获了从apo 酶到末端链转移复合物的整个转座过程，其中转座子末端与靶 DNA 共价连接，分辨率为 3.0-4.6 Å。这些结构揭示了一个蝴蝶形的复合物，经历了两轮明显的构象变化，其中转座酶的“翅膀”展开以结合底物 DNA，接近于执行切割，打开以释放侧翼 DNA，再次关闭以捕获和攻击靶 DNA。Transib 具有独特的结构元素，可以弥补 RAG2 伴侣的缺失，包括与转座靶位点相互作用的环和类似手风琴的 C 末端尾巴，该尾巴伸长和收缩以帮助控制酶的打开和关闭以及活性位点的组装。我们的发现揭示了真核剪切粘贴转座酶的详细反应途径，并阐明了 RAG 重组酶进化早期的一些步骤。
