Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA; BioNTech Cell & Gene Therapies GmbH, 55131 Mainz, Germany.
Mol Cell. 2021 Oct 21;81(20):4271-4286.e4. doi: 10.1016/j.molcel.2021.07.028. Epub 2021 Aug 16.
Helitrons are widespread eukaryotic DNA transposons that have significantly contributed to genome variability and evolution, in part because of their distinctive, replicative rolling-circle mechanism, which often mobilizes adjacent genes. Although most eukaryotic transposases form oligomers and use RNase H-like domains to break and rejoin double-stranded DNA (dsDNA), Helitron transposases contain a single-stranded DNA (ssDNA)-specific HUH endonuclease domain. Here, we report the cryo-electron microscopy structure of a Helitron transposase bound to the 5'-transposon end, providing insight into its multidomain architecture and function. The monomeric transposase forms a tightly packed assembly that buries the covalently attached cleaved end, protecting it until the second end becomes available. The structure reveals unexpected architectural similarity to TraI, a bacterial relaxase that also catalyzes ssDNA movement. The HUH active site suggests how two juxtaposed tyrosines, a feature of many replication initiators that use HUH nucleases, couple the conformational shift of an α-helix to control strand cleavage and ligation reactions.
Helitrons 是广泛存在于真核生物中的 DNA 转座子，它们通过独特的复制型滚环机制在一定程度上促进了基因组的变异性和进化，该机制常常会激活附近的基因。尽管大多数真核转座酶形成寡聚体，并利用 RNase H 样结构域来切割和重新连接双链 DNA（dsDNA），但 Helitron 转座酶含有一个单链 DNA（ssDNA）特异性的 HUH 内切酶结构域。在这里，我们报告了一个与 5'-转座子末端结合的 Helitron 转座酶的冷冻电镜结构，该结构提供了对其多结构域结构和功能的深入了解。单体转座酶形成一个紧密堆积的组装体，将共价连接的切割末端埋藏起来，直到第二个末端可用。该结构揭示了与细菌松弛酶 TraI 出人意料的结构相似性，TraI 也是一种 ssDNA 运动的催化酶。HUH 活性位点表明，许多使用 HUH 核酸酶的复制起始子的两个相邻酪氨酸如何通过构象转变来控制链切割和连接反应，这是许多复制起始子的特征。
