Jackson Ryan N, Golden Sarah M, van Erp Paul B G, Carter Joshua, Westra Edze R, Brouns Stan J J, van der Oost John, Terwilliger Thomas C, Read Randy J, Wiedenheft Blake
Department of Microbiology and Immunology, Montana State University, Bozeman, MT 59717, USA.
Laboratory of Microbiology, Department of Agrotechnology and Food Sciences, Wageningen University, Dreijenplein 10, 6703 HB Wageningen, Netherlands.
Science. 2014 Sep 19;345(6203):1473-9. doi: 10.1126/science.1256328. Epub 2014 Aug 7.
Clustered regularly interspaced short palindromic repeats (CRISPRs) are essential components of RNA-guided adaptive immune systems that protect bacteria and archaea from viruses and plasmids. In Escherichia coli, short CRISPR-derived RNAs (crRNAs) assemble into a 405-kilodalton multisubunit surveillance complex called Cascade (CRISPR-associated complex for antiviral defense). Here we present the 3.24 angstrom resolution x-ray crystal structure of Cascade. Eleven proteins and a 61-nucleotide crRNA assemble into a seahorse-shaped architecture that binds double-stranded DNA targets complementary to the crRNA-guide sequence. Conserved sequences on the 3' and 5' ends of the crRNA are anchored by proteins at opposite ends of the complex, whereas the guide sequence is displayed along a helical assembly of six interwoven subunits that present five-nucleotide segments of the crRNA in pseudo-A-form configuration. The structure of Cascade suggests a mechanism for assembly and provides insights into the mechanisms of target recognition.
成簇规律间隔短回文重复序列（CRISPRs）是RNA引导的适应性免疫系统的重要组成部分，可保护细菌和古细菌免受病毒和质粒的侵害。在大肠杆菌中，短的CRISPR衍生RNA（crRNAs）组装成一个405千道尔顿的多亚基监测复合物，称为Cascade（抗病毒防御的CRISPR相关复合物）。本文展示了Cascade的3.24埃分辨率的X射线晶体结构。11种蛋白质和一个61个核苷酸的crRNA组装成一个海马形状的结构，该结构结合与crRNA引导序列互补的双链DNA靶标。crRNA 3'和5'末端的保守序列由复合物两端的蛋白质锚定，而引导序列沿着六个交织亚基的螺旋组装展示，这些亚基以假A形式呈现crRNA的五核苷酸片段。Cascade的结构提示了一种组装机制，并为靶标识别机制提供了见解。
