Clustered regularly interspaced short palindromic repeats (CRISPR) and their CRISPR-associated proteins (Cas) provide many prokaryotes with an adaptive immune system against invading genetic material. Type III CRISPR systems are unique in that they can degrade both RNA and DNA. In response to invading nucleic acids, they produce cyclic oligoadenylates that act as secondary messengers, activating cellular nucleases that aid in the immune response. Here, we present seven single-particle cryo-EM structures of the type III-A Staphylococcus epidermidis CRISPR effector complex. The structures reveal the intact S. epidermidis effector complex in an apo, ATP-bound, cognate target RNA-bound, and non-cognate target RNA-bound states and illustrate how the effector complex binds and presents crRNA. The complexes bound to target RNA capture the type III-A effector complex in a post-RNA cleavage state. The ATP-bound structures give details about how ATP binds to Cas10 to facilitate cyclic oligoadenylate production.

成簇的规则间隔的短回文重复序列 (CRISPR) 及其 CRISPR 相关蛋白 (Cas) 为许多原核生物提供了针对入侵遗传物质的适应性免疫系统。III 型 CRISPR 系统的独特之处在于它们可以降解 RNA 和 DNA。为了响应入侵的核酸，它们产生环状寡腺苷酸，作为第二信使，激活有助于免疫反应的细胞核酸酶。在这里，我们展示了 III-A 型表皮葡萄球菌CRISPR 效应复合物的七个单粒子冷冻电镜结构。这些结构揭示了完整的S。表皮效应复合物处于 apo、ATP 结合、同源靶 RNA 结合和非同源靶 RNA 结合状态，并说明效应复合物如何结合和呈递 crRNA。与靶 RNA 结合的复合物捕获处于 RNA 裂解后状态的 III-A 型效应复合物。ATP 结合结构详细介绍了 ATP 如何与 Cas10 结合以促进环状寡腺苷酸的产生。