Structural Molecular Biology Group, Novo Nordisk Foundation Centre for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3-B, 2200 Copenhagen, Denmark.
Structural Molecular Biology Group, Novo Nordisk Foundation Centre for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3-B, 2200 Copenhagen, Denmark; State Key Laboratory of Microbial Technology, Shandong University, 72 Binhai Road, Jimo, Qingdao, Shandong 266237, P.R. China; Archaea Center, Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, Copenhagen Biocenter, 2200 Copenhagen, Denmark; State Key Laboratory of Agricultural Microbiology and College of Life Science and Technology, Huazhong Agricultural University, 430070 Wuhan, China.
Mol Cell. 2020 Sep 3;79(5):741-757.e7. doi: 10.1016/j.molcel.2020.07.008. Epub 2020 Jul 29.
Cmr-β is a type III-B CRISPR-Cas complex that, upon target RNA recognition, unleashes a multifaceted immune response against invading genetic elements, including single-stranded DNA (ssDNA) cleavage, cyclic oligoadenylate synthesis, and also a unique UA-specific single-stranded RNA (ssRNA) hydrolysis by the Cmr2 subunit. Here, we present the structure-function relationship of Cmr-β, unveiling how binding of the target RNA regulates the Cmr2 activities. Cryoelectron microscopy (cryo-EM) analysis revealed the unique subunit architecture of Cmr-β and captured the complex in different conformational stages of the immune response, including the non-cognate and cognate target-RNA-bound complexes. The binding of the target RNA induces a conformational change of Cmr2, which together with the complementation between the 5' tag in the CRISPR RNAs (crRNA) and the 3' antitag of the target RNA activate different configurations in a unique loop of the Cmr3 subunit, which acts as an allosteric sensor signaling the self- versus non-self-recognition. These findings highlight the diverse defense strategies of type III complexes.
Cmr-β 是一种 III-B 型 CRISPR-Cas 复合物，在识别靶 RNA 后，针对入侵的遗传元件引发多种免疫反应，包括单链 DNA（ssDNA）切割、环寡腺苷酸合成，以及 Cmr2 亚基对独特的 UA 特异性单链 RNA（ssRNA）的水解。在这里，我们展示了 Cmr-β 的结构-功能关系，揭示了靶 RNA 结合如何调节 Cmr2 的活性。冷冻电镜（cryo-EM）分析揭示了 Cmr-β 的独特亚基结构，并捕获了免疫反应不同构象阶段的复合物，包括非同源和同源靶 RNA 结合复合物。靶 RNA 的结合诱导 Cmr2 的构象变化，与 CRISPR RNA（crRNA）中的 5'标签和靶 RNA 的 3'反标签之间的互补一起，激活 Cmr3 亚基独特环中的不同构象，该环作为别构传感器，发出自我识别与非自我识别的信号。这些发现强调了 III 型复合物的多种防御策略。
