8qbm
Retron-Eco1 filament with ADP-ribosylated Effector (full map with 2 segments)
Structural highlights
FunctionRT86_ECOLX Reverse transcriptase (RT) component of antiviral defense system retron Ec86, composed of a non-coding RNA (ncRNA), a ribosyltransferase/DNA-binding protein and this RT. Expression of the 3-gene retron 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 (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:10531319, PubMed:2466573). Recognizes only its cognate RNA as a primer template (PubMed:10531319). Overexpression of the ncRNA and RT (without the ribosyltransferase), which leads to increased levels of msDNA, is mutagenic in vivo (PubMed:7885227). This may be due to a mismatch in the msDNA stem which binds and sequesters MutS and/or MutL (Probable).[1] [2] [3] [4] [5] Publication Abstract from PubMedRetrons are toxin-antitoxin systems protecting bacteria against bacteriophages via abortive infection. The Retron-Eco1 antitoxin is formed by a reverse transcriptase (RT) and a non-coding RNA (ncRNA)/multi-copy single-stranded DNA (msDNA) hybrid that neutralizes an uncharacterized toxic effector. Yet, the molecular mechanisms underlying phage defense remain unknown. Here, we show that the N-glycosidase effector, which belongs to the STIR superfamily, hydrolyzes NAD(+) during infection. Cryoelectron microscopy (cryo-EM) analysis shows that the msDNA stabilizes a filament that cages the effector in a low-activity state in which ADPr, a NAD(+) hydrolysis product, is covalently linked to the catalytic E106 residue. Mutations shortening the msDNA induce filament disassembly and the effector's toxicity, underscoring the msDNA role in immunity. Furthermore, we discovered a phage-encoded Retron-Eco1 inhibitor (U56) that binds ADPr, highlighting the intricate interplay between retron systems and phage evolution. Our work outlines the structural basis of Retron-Eco1 defense, uncovering ADPr's pivotal role in immunity. Retron-Eco1 assembles NAD(+)-hydrolyzing filaments that provide immunity against bacteriophages.,Carabias A, Camara-Wilpert S, Mestre MR, Lopez-Mendez B, Hendriks IA, Zhao R, Pape T, Fuglsang A, Luk SH, Nielsen ML, Pinilla-Redondo R, Montoya G Mol Cell. 2024 May 18:S1097-2765(24)00394-0. doi: 10.1016/j.molcel.2024.05.001. PMID:38788717[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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