9exh
Cryo-EM structure of the Apo E. coli BrxX methyltransferase
Structural highlights
FunctionPGLX_ECOHS BREX systems (bacteriophage exclusion) provide immunity against bacteriophage. Part of a type 1 BREX system which protects against dsDNA phage. This system allows phage adsorption but prevents phage DNA replication, without degradation of the phage DNA. Methylation of bacterial DNA by this protein guides self/non-self discrimination. When the brxA-brxB-brxC-pglX-pglZ-brxL genes are transformed into a susceptible E.coli strain (BW25113) they confer very high resistance to infection by bacteriophage VR7 and VpaE1, about 100-fold protection against lambda, T5 and T7 (probably with a mutated 0.3 gene) and no protection against RNA phage Qbeta, ssDNA phage M13 or dSDNA phage T4 and VR5. Glycosylated phage DNA is not susceptible to BREX. The BREX system does not confer resistance to lysogenic lambda phage, i.e. prophage that are integrated into the chromosomal DNA and then induced to form phage.[1] [2] Methylates the adenine in the fifth position of the hexamer 5'-GGTAAG-3' in genomic DNA; methylates the same sequence in the few phage that escape the BREX system. Methylated phage are now resistant to BREX, showing immunity is provided by an epigenetic modification. Expression of this protein alone has no effect on phage infection, does not lead to methylated DNA and mildly inhibits growth.[3] Publication Abstract from PubMedAnti-phage systems of the BREX (BacteRiophage EXclusion) superfamily rely on site-specific epigenetic DNA methylation to discriminate between the host and invading DNA. We demonstrate that in Type I BREX systems, defense and methylation require BREX site DNA binding by the BrxX (PglX) methyltransferase employing S-adenosyl methionine as a cofactor. We determined 2.2-A cryoEM structure of Escherichia coli BrxX bound to target dsDNA revealing molecular details of BREX DNA recognition. Structure-guided engineering of BrxX expands its DNA specificity and dramatically enhances phage defense. We show that BrxX alone does not methylate DNA, and BREX activity requires an assembly of a supramolecular BrxBCXZ immune complex. Finally, we present a cryoEM structure of BrxX bound to a phage-encoded inhibitor Ocr that sequesters BrxX in an inactive dimeric form. We propose that BrxX-mediated foreign DNA sensing is a necessary first step in activation of BREX defense. Molecular basis of foreign DNA recognition by BREX anti-phage immunity system.,Drobiazko A, Adams MC, Skutel M, Potekhina K, Kotovskaya O, Trofimova A, Matlashov M, Yatselenko D, Maxwell KL, Blower TR, Severinov K, Ghilarov D, Isaev A Nat Commun. 2025 Feb 20;16(1):1825. doi: 10.1038/s41467-025-57006-2. PMID:39979294[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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