Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA; McGovern Institute for Brain Research at MIT, Cambridge, MA 02139, USA; Department of Brain and Cognitive Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Howard Hughes Medical Institute, Cambridge, MA 02139, USA.
Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA; McGovern Institute for Brain Research at MIT, Cambridge, MA 02139, USA; Department of Brain and Cognitive Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA; Howard Hughes Medical Institute, Cambridge, MA 02139, USA.
Mol Cell. 2024 Aug 22;84(16):3154-3162.e5. doi: 10.1016/j.molcel.2024.07.026. Epub 2024 Aug 6.
Canonical prokaryotic type I CRISPR-Cas adaptive immune systems contain a multicomponent effector complex called Cascade, which degrades large stretches of DNA via Cas3 helicase-nuclease activity. Recently, a highly precise subtype I-F1 CRISPR-Cas system (HNH-Cascade) was found that lacks Cas3, the absence of which is compensated for by the insertion of an HNH endonuclease domain in the Cas8 Cascade component. Here, we describe the cryo-EM structure of Selenomonas sp. HNH-Cascade (SsCascade) in complex with target DNA and characterize its mechanism of action. The Cascade scaffold is complemented by the HNH domain, creating a ring-like structure in which the unwound target DNA is precisely cleaved. This structure visualizes a unique hybrid of two extensible biological systems-Cascade, an evolutionary platform for programmable DNA effectors, and an HNH nuclease, an adaptive domain with a spectrum of enzymatic activity.
经典的原核 I 型 CRISPR-Cas 适应性免疫系统包含一个称为 Cascade 的多组分效应复合物，该复合物通过 Cas3 解旋酶-核酸酶活性降解大片段 DNA。最近，发现了一种高度精确的 I-F1 CRISPR-Cas 系统（HNH-Cascade），该系统缺乏 Cas3，但其 Cas8 Cascade 组分中插入了一个 HNH 内切酶结构域，从而弥补了 Cas3 的缺失。在这里，我们描述了 Selenomonas sp. HNH-Cascade（SsCascade）与靶 DNA 形成的复合物的冷冻电镜结构，并对其作用机制进行了表征。Cascade 支架由 HNH 结构域补充，形成一个环状结构，其中解开的靶 DNA 被精确切割。该结构直观地展示了两种可扩展生物系统的独特融合：Cascade 是可编程 DNA 效应物的进化平台，而 HNH 核酸酶则是具有多种酶活性的适应性结构域。
Zotero 插件
