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Cryo-EM structure of E.coli retron-Ec86 in complex with its effector at 2.5 angstrom
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 PubMedFirst discovered in the 1980s, retrons are bacterial genetic elements consisting of a reverse transcriptase and a non-coding RNA (ncRNA). Retrons mediate antiphage defence in bacteria but their structure and defence mechanisms are unknown. Here, we investigate the Escherichia coli Ec86 retron and use cryo-electron microscopy to determine the structures of the Ec86 (3.1 A) and cognate effector-bound Ec86 (2.5 A) complexes. The Ec86 reverse transcriptase exhibits a characteristic right-hand-like fold consisting of finger, palm and thumb subdomains. Ec86 reverse transcriptase reverse-transcribes part of the ncRNA into satellite, multicopy single-stranded DNA (msDNA, a DNA-RNA hybrid) that we show wraps around the reverse transcriptase electropositive surface. In msDNA, both inverted repeats are present and the 3' sides of the DNA/RNA chains are close to the reverse transcriptase active site. The Ec86 effector adopts a two-lobe fold and directly binds reverse transcriptase and msDNA. These findings offer insights into the structure-function relationship of the retron-effector unit and provide a structural basis for the optimization of retron-based genome editing systems. Cryo-EM structures of Escherichia coli Ec86 retron complexes reveal architecture and defence mechanism.,Wang Y, Guan Z, Wang C, Nie Y, Chen Y, Qian Z, Cui Y, Xu H, Wang Q, Zhao F, Zhang D, Tao P, Sun M, Yin P, Jin S, Wu S, Zou T Nat Microbiol. 2022 Sep;7(9):1480-1489. doi: 10.1038/s41564-022-01197-7. Epub , 2022 Aug 18. PMID:35982312[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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