Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing Key Laboratory of Bioprocess, State Key Laboratory of Chemical Resource Engineering, College of Life Science and Technology, Beijing University of Chemical Technology, Beijing 100029, China.
Ministry of Education Key Laboratory of Protein Science, Beijing Advanced Innovation Center for Structural Biology, Beijing Frontier Research Center for Biological Structure, School of Life Sciences, Tsinghua University, Tsinghua-Peking Center for Life Sciences, Beijing 100084, China.
Mol Cell. 2022 Dec 1;82(23):4503-4518.e8. doi: 10.1016/j.molcel.2022.10.007. Epub 2022 Oct 27.
In the type III-E CRISPR-Cas system, a Cas effector (gRAMP) is associated with a TPR-CHAT to form Craspase (CRISPR-guided caspase). However, both the structural features of gRAMP and the immunity mechanism remain unknown for this system. Here, we report structures of gRAMP-crRNA and gRAMP:cRNA:target RNA as well as structures of Craspase and Craspase complexed with cognate target RNA (CTR) or non-cognate target RNA (NTR). Importantly, the 3' anti-tag region of NTR and CTR binds at two distinct channels in Craspase, and CTR with a non-complementary 3' anti-tag induces a marked conformational change of the TPR-CHAT, which allosterically activates its protease activity to cleave an ancillary protein Csx30. This cleavage then triggers an abortive infection as the antiviral strategy of the type III-E system. Together, our study provides crucial insights into both the catalytic mechanism of the gRAMP and the immunity mechanism of the type III-E system.
在 III-E 型 CRISPR-Cas 系统中，Cas 效应蛋白（gRAMP）与 TPR-CHAT 相关联，形成 Craspase（CRISPR 引导的 Caspase）。然而，对于该系统，gRAMP 的结构特征和免疫机制仍不清楚。在这里，我们报告了 gRAMP-crRNA 和 gRAMP:cRNA:target RNA 的结构，以及 Craspase 及其与同源靶 RNA（CTR）或非同源靶 RNA（NTR）复合物的结构。重要的是，NTR 和 CTR 的 3' 反标签区域结合在 Craspase 的两个不同通道中，并且具有非互补 3' 反标签的 CTR 诱导 TPR-CHAT 的明显构象变化，这使其蛋白酶活性别构激活，从而切割辅助蛋白 Csx30。这种切割随后触发了一种流产感染，这是 III-E 型系统的抗病毒策略。总之，我们的研究为 gRAMP 的催化机制和 III-E 型系统的免疫机制提供了重要的见解。
