9lpa
From Proteopedia
The cryo-EM structure of retron Eco8 in an active state
Structural highlights
FunctionOLD8_ECOLX Probable nuclease member of antiviral defense system retron Eco8, composed of an reverse transcriptase (RT), this nuclease and a non-coding RNA (ncRNA) encoded between them. Expression of retron Eco8 confers protection against bacteriophages T4, T6, T7 and SECphi4, SECphi6 and SECphi18. At multiplicity of infection (MOI) of 0.02 cultures slow growth when infected with SECphi4 but do not collapse, at MOI 2 cultures collapse. When the retron is cloned in another E.coli strain synthesizes msDNA (a branched RNA linked by a 2',5'-phosphodiester bond to a single-stranded DNA). The retron transcript serves as primer and template to the reaction, and codes for the RT.[1] Publication Abstract from PubMedEscherichia coli Eco8 is an anti-phage defense system consisting of a reverse transcriptase, a class 3 overcoming lysogenization defect (OLD) nuclease, and a DNA-RNA chimera called multi-copy single-stranded DNA (msDNA). Genetic and biochemical data suggest that Eco8-mediated anti-phage defense is triggered by the phage single-stranded DNA (ssDNA)-binding proteins, but the underlying structural basis remains unknown. Here, we demonstrate that the DNA cleavage and ATP hydrolysis activities of the OLD nuclease are critical for Eco8-mediated anti-phage defense. We also determine the cryoelectron microscopy (cryo-EM) structures of Eco8 alone and in complex with the T7 phage ssDNA-binding protein. Structural analysis reveals that the reverse transcriptase, msDNA, and OLD nuclease form a megacomplex with a 4:4:4 stoichiometry. The T7 phage ssDNA-binding protein unwinds the msDNA and transforms Eco8 into an ATP-dependent DNA-degrading machinery. This study not only elucidates the molecular mechanism of Eco8-mediated anti-phage defense but also validates that msDNA serves as a sensor of phage DNA-modifying/binding proteins. Molecular mechanism of Eco8-mediated anti-phage defense.,Yuan L, Xu L, Wu B, Liu Q, Yao Y, Hua X, Feng Y Mol Cell. 2025 Oct 30:S1097-2765(25)00814-7. doi: 10.1016/j.molcel.2025.09.029. PMID:41172990[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
| ||||||||||||||||||||
