Wang Yanjing, Wang Chen, Yin Yongqi, Cui Yongqing, Dai Zhikang, Liu Chang, Chen Yanke, Guan Zeyuan, Zou Tingting
National Key Laboratory of Agricultural Microbiology, Hubei Hongshan Laboratory, Huazhong Agricultural University, Wuhan, Hubei, China.
Department of Pathology, UMass Chan Medical School, Worcester, MA, USA.
Cell Discov. 2025 Sep 2;11(1):73. doi: 10.1038/s41421-025-00823-y.
In the evolutionary arms race between bacteria and viruses, retrons have emerged as distinctive antiphage defense systems. Here, we elucidate the structure and function of Retron-Eco2, which comprises a non-coding RNA (ncRNA) that encodes multicopy single-stranded DNA (msDNA, a DNA‒RNA hybrid) and a fusion protein containing a reverse transcriptase (RT) domain and a topoisomerase-primase-like (Toprim) effector domain. The Eco2 msDNA and RT-Toprim fusion protein form a 1:1 stoichiometric nucleoprotein complex that further assembles into a trimer (msDNA:RT-Toprim ratio of 3:3) with a distinctive triangular configuration. The RNA portion of the msDNA in one protomer closely intertwines around the RT domain of an adjacent protomer, mediating the formation of this self-inhibitory assembly. Upon activation, the Toprim effector domain exhibits RNase activity, degrading RNA to arrest phage replication. We further reveal that phage mutants evading Eco2-mediated defense harbor mutations in the endonuclease IV-like protein DenB, underscoring DenB's critical role in triggering the activation of this system. Together, these findings provide key structural and functional insights into Retron-Eco2, laying the groundwork for harnessing its potential in biotechnology and synthetic biology applications.
在细菌与病毒的进化军备竞赛中，逆转录子已成为独特的抗噬菌体防御系统。在此，我们阐明了Retron-Eco2的结构与功能，它由编码多拷贝单链DNA（msDNA，一种DNA-RNA杂交体）的非编码RNA（ncRNA）以及包含逆转录酶（RT）结构域和拓扑异构酶-引发酶样（Toprim）效应结构域的融合蛋白组成。Eco2 msDNA与RT-Toprim融合蛋白形成1:1化学计量的核蛋白复合物，该复合物进一步组装成具有独特三角形结构的三聚体（msDNA:RT-Toprim比例为3:3）。一个原体中msDNA的RNA部分紧密缠绕在相邻原体的RT结构域周围，介导了这种自我抑制性组装的形成。激活后，Toprim效应结构域表现出RNase活性，降解RNA以阻止噬菌体复制。我们进一步揭示，逃避Eco2介导防御的噬菌体突变体在内切核酸酶IV样蛋白DenB中存在突变，这突出了DenB在触发该系统激活中的关键作用。总之，这些发现为Retron-Eco2提供了关键的结构和功能见解，为在生物技术和合成生物学应用中利用其潜力奠定了基础。
