9lm3
cryo-EM structure of retron Eco2
Structural highlights
FunctionRT67_ECOLX Reverse transcriptase (RT) component of antiviral defense system retron Ec67, minimally composed of a non-coding RNA (ncRNA) and this RT. Expression of these 2 elements confers protection against bacteriophage T5. At multiplicity of infection (MOI) of 0.02 cultures grow normally when infected with T5 without collapsing, at MOI 2 cultures enter growth stasis (PubMed:33157039). Responsible for synthesis of msDNA-Ec67 (a branched molecule with RNA linked by a 2',5'-phosphodiester bond to ssDNA). The retron transcript serves as primer (from a conserved internal G residue) and template for the reaction, and codes for the RT (PubMed:1378431, PubMed:1692831, PubMed:2466332). Can use other retrons as substrate (msDNA-Mx162 and msDNA-Ec86). Also able to synthesize DNA from a DNA template at least in vitro, although the enzyme is less active with a DNA template (PubMed:1692831).[1] [2] [3] [4] Publication Abstract from PubMedIn 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 DNAâRNA 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. Structural basis of the RNA-mediated Retron-Eco2 oligomerization.,Wang Y, Wang C, Yin Y, Cui Y, Dai Z, Liu C, Chen Y, Guan Z, Zou T Cell Discov. 2025 Sep 2;11(1):73. doi: 10.1038/s41421-025-00823-y. PMID:40897710[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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