ジャーナル: Nature / 年: 2020 タイトル: Structural basis of DNA targeting by a transposon-encoded CRISPR-Cas system. 著者: Tyler S Halpin-Healy / Sanne E Klompe / Samuel H Sternberg / Israel S Fernández / 要旨: Bacteria use adaptive immune systems encoded by CRISPR and Cas genes to maintain genomic integrity when challenged by pathogens and mobile genetic elements. Type I CRISPR-Cas systems typically ...Bacteria use adaptive immune systems encoded by CRISPR and Cas genes to maintain genomic integrity when challenged by pathogens and mobile genetic elements. Type I CRISPR-Cas systems typically target foreign DNA for degradation via joint action of the ribonucleoprotein complex Cascade and the helicase-nuclease Cas3, but nuclease-deficient type I systems lacking Cas3 have been repurposed for RNA-guided transposition by bacterial Tn7-like transposons. How CRISPR- and transposon-associated machineries collaborate during DNA targeting and insertion remains unknown. Here we describe structures of a TniQ-Cascade complex encoded by the Vibrio cholerae Tn6677 transposon using cryo-electron microscopy, revealing the mechanistic basis of this functional coupling. The cryo-electron microscopy maps enabled de novo modelling and refinement of the transposition protein TniQ, which binds to the Cascade complex as a dimer in a head-to-tail configuration, at the interface formed by Cas6 and Cas7 near the 3' end of the CRISPR RNA (crRNA). The natural Cas8-Cas5 fusion protein binds the 5' crRNA handle and contacts the TniQ dimer via a flexible insertion domain. A target DNA-bound structure reveals critical interactions necessary for protospacer-adjacent motif recognition and R-loop formation. This work lays the foundation for a structural understanding of how DNA targeting by TniQ-Cascade leads to downstream recruitment of additional transposase proteins, and will guide protein engineering efforts to leverage this system for programmable DNA insertions in genome-engineering applications.
#89 - 2007年5月 アコニターゼと鉄調節タンパク質1 (Aconitase and Iron Regulatory Protein 1) 類似性 (1)
#241 - 2020年1月 20年の分子を振り返って (Twenty Years of Molecules) 類似性 (2)
-
集合体
登録構造単位
A: cas7 type I-F CRISPR-associated protein Csy3 B: cas7 type I-F CRISPR-associated protein Csy3 C: cas7 type I-F CRISPR-associated protein Csy3 D: cas7 type I-F CRISPR-associated protein Csy3 E: cas7 type I-F CRISPR-associated protein Csy3 F: cas7 type I-F CRISPR-associated protein Csy3 G: cas5_8 naturally occurring fusion protein H: type I-F CRISPR-associated endoribonuclease Cas6/Csy4 I: TniQ monomer I J: TniQ monomer 2 1: guide RNA 2: Targeting strand ssDNA 3: Non-targeting strand ssDNA