2023年8月8日，来自美国普渡大学Leifu Chang研究小组在学术期刊《细胞》上发表了标题为“Molecular mechanism for Tn7-like transposon recruitment by a type I-B CRISPR effector. ”的研究成果，揭示I-B型CRISPR效应器招募Tn7样转座子的分子机制。
研究人员表示，Tn7样转座子与CRISPR-Cas系统合作，促进了自身DNA的移动。这些CRISPR相关转座子（CAST）是可编程基因敲除的有望工具。CAST的一个主要特点是能够将Tn7样转座子招募到核酸酶缺陷的CRISPR效应器上。然而，人们对Tn7样转座子是如何被不同的CRISPR效应器招募的仍然知之甚少。
研究人员展示了由Cascade复合物、TniQ、TnsC和来自Peltigera membranacea cyanobiont 210A的I-B型CAST中的靶标DNA组成的招募复合物冷冻电镜结构。Cascade对靶标DNA的识别会诱导Cas6发生构象变化，并通过其C端结构域启动TniQ的招募。TniQ的N端结构域与TnsC螺旋七聚体的接缝区域结合。这项发现让人们深入了解了Tn7样转座子招募到CRISPR效应器的不同机制，并将有助于开发CAST作为基因敲除工具。
Highlights
•Biochemical reconstitution and discovery of Cas11 in type I-B2 PmcCAST
•Cryo-EM structure of the Cascade-DNA-TniQ-TnsC recruitment complex
•Target DNA binding promotes conformational changes in Cascade to recruit TniQ
•TniQ binds to the seam region of the TnsC spiral heptamer
Summary
Tn7-like transposons have co-opted CRISPR-Cas systems to facilitate the movement of their own DNA. These CRISPR-associated transposons (CASTs) are promising tools for programmable gene knockin. A key feature of CASTs is their ability to recruit Tn7-like transposons to nuclease-deficient CRISPR effectors. However, how Tn7-like transposons are recruited by diverse CRISPR effectors remains poorly understood. Here, we present the cryo-EM structure of a recruitment complex comprising the Cascade complex, TniQ, TnsC, and the target DNA in the type I-B CAST from Peltigera membranacea cyanobiont 210A. Target DNA recognition by Cascade induces conformational changes in Cas6 and primes TniQ recruitment through its C-terminal domain. The N-terminal domain of TniQ is bound to the seam region of the TnsC spiral heptamer. Our findings provide insights into the diverse mechanisms for the recruitment of Tn7-like transposons to CRISPR effectors and will aid in the development of CASTs as gene knockin tools.
文章来源：
Shukun Wang, Clinton Gabel et al, Molecular mechanism for Tn7-like transposon recruitment by a type I-B CRISPR effector. DOI: 10.1016/j.cell.2023.07.010, 最新IF：66.85
