Department of Microbiology and Immunology, Montana State University, Bozeman, MT 59717, USA.
Department of Integrative Structural and Computational Biology, Scripps Research Institute, La Jolla, CA, USA.
Mol Cell. 2019 Apr 4;74(1):132-142.e5. doi: 10.1016/j.molcel.2019.02.001. Epub 2019 Mar 11.
Bacteria and archaea have evolved sophisticated adaptive immune systems that rely on CRISPR RNA (crRNA)-guided detection and nuclease-mediated elimination of invading nucleic acids. Here, we present the cryo-electron microscopy (cryo-EM) structure of the type I-F crRNA-guided surveillance complex (Csy complex) from Pseudomonas aeruginosa bound to a double-stranded DNA target. Comparison of this structure to previously determined structures of this complex reveals a ∼180-degree rotation of the C-terminal helical bundle on the "large" Cas8f subunit. We show that the double-stranded DNA (dsDNA)-induced conformational change in Cas8f exposes a Cas2/3 "nuclease recruitment helix" that is structurally homologous to a virally encoded anti-CRISPR protein (AcrIF3). Structural homology between Cas8f and AcrIF3 suggests that AcrIF3 is a mimic of the Cas8f nuclease recruitment helix.
细菌和古菌已经进化出复杂的适应性免疫系统，依赖于 CRISPR RNA (crRNA)引导的检测和核酸酶介导的入侵核酸的消除。在这里，我们展示了来自铜绿假单胞菌的 I-F 型 crRNA 引导的监测复合物 (Csy 复合物)与双链 DNA 靶标结合的低温电子显微镜 (cryo-EM) 结构。将这个结构与之前确定的这个复合物的结构进行比较，揭示了“大”Cas8f 亚基上 C 末端螺旋束的约 180 度旋转。我们表明，双链 DNA (dsDNA)诱导的 Cas8f 构象变化暴露了 Cas2/3“核酸酶招募螺旋”，该螺旋在结构上与病毒编码的抗 CRISPR 蛋白 (AcrIF3)同源。Cas8f 和 AcrIF3 之间的结构同源性表明，AcrIF3 是 Cas8f 核酸酶招募螺旋的模拟物。
