Structure of the IscB–ωRNA ribonucleoprotein complex, the likely ancestor of CRISPR-Cas9

• DOI: 10.1038/s41467-022-34378-3
• Publication Date: 2022-11-07T20:03:56Z
• Authors: Kazuki Kato; Sae Okazaki; Soumya Kannan; Han Altae-Tran; F. Esra Demircioglu; Yukari Isayama; Junichiro Ishikawa; Masahiro Fukuda; Rhiannon K. Macrae; Tomohiro Nishizawa; Kira S. Makarova; Eugene V. Koonin; Feng Zhang; Hiroshi Nishimasu
• Keywords: 0303 health sciences; Science; Q; Cryoelectron Microscopy; DNA; Endonucleases; Article; 03 medical and health sciences; Ribonucleoproteins; Humans; RNA; CRISPR-Cas Systems; RNA, Guide, Kinetoplastida

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