7btp
From Proteopedia
EcoR124I-Ocr in Restriction-Alleviation State
Structural highlights
Function[T1S1_ECOLX] The M and S subunits together form a methyltransferase (MTase) that methylates two adenine residues in complementary strands of a bipartite DNA recognition sequence. In the presence of the R subunit the complex can also act as an endonuclease, binding to the same target sequence but cutting the DNA some distance from this site. Whether the DNA is cut or modified depends on the methylation state of the target sequence. When the target site is unmodified, the DNA is cut. When the target site is hemimethylated, the complex acts as a maintenance MTase modifying the DNA so that both strands become methylated. Subunit S dictates DNA sequences specificity. The EcoR124/3i enzyme recognizes 5'-GAAN(6)RTCG-3'. [T1M1_ECOLX] Methylation of specific adenine residues; required for both restriction and modification activities (By similarity). The EcoR124/3 I enzyme recognizes 5'-GAAN(7)RTCG-3'. Publication Abstract from PubMedType I restriction-modification (R-M) systems are widespread in prokaryotic genomes and provide robust protection against foreign DNA. They are multisubunit enzymes with methyltransferase, endonuclease and translocase activities. Despite extensive studies over the past five decades, little is known about the molecular mechanisms of these sophisticated machines. Here, we report the cryo-electron microscopy structures of the representative EcoR124I R-M system in different assemblies (R2M2S1, R1M2S1 and M2S1) bound to target DNA and the phage and mobile genetic element-encoded anti-restriction proteins Ocr and ArdA. EcoR124I can precisely regulate different enzymatic activities by adopting distinct conformations. The marked conformational transitions of EcoR124I are dependent on the intrinsic flexibility at both the individual-subunit and assembled-complex levels. Moreover, Ocr and ArdA use a DNA-mimicry strategy to inhibit multiple activities, but do not block the conformational transitions of the complexes. These structural findings, complemented by mutational studies of key intermolecular contacts, provide insights into assembly, operation and inhibition mechanisms of type I R-M systems. Structural insights into assembly, operation and inhibition of a type I restriction-modification system.,Gao Y, Cao D, Zhu J, Feng H, Luo X, Liu S, Yan XX, Zhang X, Gao P Nat Microbiol. 2020 Jun 1. pii: 10.1038/s41564-020-0731-z. doi:, 10.1038/s41564-020-0731-z. PMID:32483229[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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