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引用次数: 0
摘要
典型的原核生物I型CRISPR-Cas适应性免疫系统包含一个名为 "级联"(Cascade)的多组分效应复合体,它通过Cas3螺旋酶-核酸酶活性降解大段DNA。最近,我们发现了一种高度精确的 I-F1 亚型 CRISPR-Cas 系统(HNH-Cascade),它缺乏 Cas3,但通过在 Cas8 Cascade 成分中插入一个 HNH 内切酶结构域来弥补。在这里,我们描述了硒单胞菌 HNH-Cascade(SsCascade)与靶 DNA 复合物的冷冻电镜结构,并描述了其作用机制。HNH 结构域对级联支架进行了补充,从而形成了一种环状结构,在这种结构中,解旋的目标 DNA 被精确地裂解。该结构展示了两个可扩展生物系统的独特混合体--Cascade(可编程 DNA 效应器的进化平台)和 HNH 核酸酶(具有多种酶活性的适应性结构域)。
Structural determinants of DNA cleavage by a CRISPR HNH-Cascade system
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.
期刊介绍:
Molecular Cell is a companion to Cell, the leading journal of biology and the highest-impact journal in the world. Launched in December 1997 and published monthly. Molecular Cell is dedicated to publishing cutting-edge research in molecular biology, focusing on fundamental cellular processes. The journal encompasses a wide range of topics, including DNA replication, recombination, and repair; Chromatin biology and genome organization; Transcription; RNA processing and decay; Non-coding RNA function; Translation; Protein folding, modification, and quality control; Signal transduction pathways; Cell cycle and checkpoints; Cell death; Autophagy; Metabolism.