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.
#241 - 2020年1月 20年の分子を振り返って (Twenty Years of Molecules) 類似性 (1)
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集合体
登録構造単位
A: Cas7, type I-F CRISPR-associated protein B: Cas7, type I-F CRISPR-associated protein C: Cas7, type I-F CRISPR-associated protein D: Cas7, type I-F CRISPR-associated protein E: Cas7, type I-F CRISPR-associated protein F: Cas7, type I-F CRISPR-associated protein G: cas5_8 naturally occurring fusion protein H: type I-F CRISPR-associated endoribonuclease Cas6/Csy4 I: TniQ monomer 1 J: TniQ monomer 2 1: guide RNA (60-MER)
装置: FEI VITROBOT MARK II / 凍結剤: ETHANE / 湿度: 100 % / 凍結前の試料温度: 4 K
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電子顕微鏡撮影
実験機器
モデル: Tecnai Polara / 画像提供: FEI Company
顕微鏡
モデル: FEI POLARA 300
電子銃
電子線源: FIELD EMISSION GUN / 加速電圧: 300 kV / 照射モード: OTHER
電子レンズ
モード: BRIGHT FIELD
撮影
電子線照射量: 50 e/Å2 / フィルム・検出器のモデル: GATAN K3 (6k x 4k)
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解析
ソフトウェア
名称
バージョン
分類
NB
REFMAC
5.8.0238
精密化
PDB_EXTRACT
3.25
データ抽出
EMソフトウェア
名称: RELION / バージョン: 3 / カテゴリ: 最終オイラー角割当
CTF補正
タイプ: PHASE FLIPPING AND AMPLITUDE CORRECTION
対称性
点対称性: C1 (非対称)
3次元再構成
解像度: 3.4 Å / 解像度の算出法: FSC 0.143 CUT-OFF / 粒子像の数: 85000 / アルゴリズム: BACK PROJECTION / 対称性のタイプ: POINT
精密化
解像度: 3.4→3.4 Å / Cor.coef. Fo:Fc: 0.852 / SU B: 26.769 / SU ML: 0.385 / 交差検証法: THROUGHOUT / σ(F): 0 / ESU R: 0.819 立体化学のターゲット値: MAXIMUM LIKELIHOOD WITH PHASES 詳細: HYDROGENS HAVE BEEN ADDED IN THE RIDING POSITIONS U VALUES : REFINED INDIVIDUALLY
Rfactor
反射数
%反射
Rwork
0.3305
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obs
0.3305
176517
100 %
溶媒の処理
イオンプローブ半径: 0.8 Å / 減衰半径: 0.8 Å / VDWプローブ半径: 1.2 Å / 溶媒モデル: MASK