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Publication Abstract from PubMed

Transposon-encoded IscB family proteins are RNA-guided nucleases in the OMEGA (obligate mobile element-guided activity) system, and likely ancestors of the RNA-guided nuclease Cas9 in the type II CRISPR-Cas adaptive immune system. IscB associates with its cognate omegaRNA to form a ribonucleoprotein complex that cleaves double-stranded DNA targets complementary to an omegaRNA guide segment. Although IscB shares the RuvC and HNH endonuclease domains with Cas9, it is much smaller than Cas9, mainly due to the lack of the alpha-helical nucleic-acid recognition lobe. Here, we report the cryo-electron microscopy structure of an IscB protein from the human gut metagenome (OgeuIscB) in complex with its cognate omegaRNA and a target DNA, at 2.6-A resolution. This high-resolution structure reveals the detailed architecture of the IscB-omegaRNA ribonucleoprotein complex, and shows how the small IscB protein assembles with the omegaRNA and mediates RNA-guided DNA cleavage. The large omegaRNA scaffold structurally and functionally compensates for the recognition lobe of Cas9, and participates in the recognition of the guide RNA-target DNA heteroduplex. These findings provide insights into the mechanism of the programmable DNA cleavage by the IscB-omegaRNA complex and the evolution of the type II CRISPR-Cas9 effector complexes.

Structure of the IscB-omegaRNA ribonucleoprotein complex, the likely ancestor of CRISPR-Cas9.,Kato K, Okazaki S, Kannan S, Altae-Tran H, Esra Demircioglu F, Isayama Y, Ishikawa J, Fukuda M, Macrae RK, Nishizawa T, Makarova KS, Koonin EV, Zhang F, Nishimasu H Nat Commun. 2022 Nov 7;13(1):6719. doi: 10.1038/s41467-022-34378-3. PMID:36344504^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.