Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208, USA.
Nucleic Acids Res. 2019 Apr 23;47(7):3765-3783. doi: 10.1093/nar/gkz079.
Clustered regularly interspaced short palindromic repeats (CRISPR) and their associated Cas proteins provide an immune-like response in many prokaryotes against extraneous nucleic acids. CRISPR-Cas systems are classified into different classes and types. Class 1 CRISPR-Cas systems form multi-protein effector complexes that includes a guide RNA (crRNA) used to identify the target for destruction. Here we present crystal structures of Staphylococcus epidermidis Type III-A CRISPR subunits Csm2 and Csm3 and a 5.2 Å resolution single-particle cryo-electron microscopy (cryo-EM) reconstruction of an in vivo assembled effector subcomplex including the crRNA. The structures help to clarify the quaternary architecture of Type III-A effector complexes, and provide details on crRNA binding, target RNA binding and cleavage, and intermolecular interactions essential for effector complex assembly. The structures allow a better understanding of the organization of Type III-A CRISPR effector complexes as well as highlighting the overall similarities and differences with other Class 1 effector complexes.
成簇规律间隔短回文重复序列（CRISPR）及其相关的 Cas 蛋白为许多原核生物提供了一种针对外来核酸的免疫样反应。CRISPR-Cas 系统被分为不同的类别和类型。第 1 类 CRISPR-Cas 系统形成多蛋白效应复合物，其中包括用于识别靶标进行破坏的指导 RNA（crRNA）。在这里，我们展示了表皮葡萄球菌 III-A 型 CRISPR 亚基 Csm2 和 Csm3 的晶体结构，以及包括 crRNA 的体内组装效应子亚复合物的 5.2 Å 分辨率单颗粒冷冻电镜（cryo-EM）重建。这些结构有助于阐明 III-A 型效应子复合物的四级结构，并提供有关 crRNA 结合、靶 RNA 结合和切割以及对于效应子复合物组装至关重要的分子间相互作用的详细信息。这些结构使我们能够更好地理解 III-A 型 CRISPR 效应子复合物的组织，同时突出了与其他第 1 类效应子复合物的总体相似性和差异。
