Department of Biological Sciences, Purdue University, West Lafayette, IN, USA.
Department of Microbiology and Immunology, University of California, San Francisco, San Francisco, CA, USA.
Nat Chem Biol. 2022 Dec;18(12):1417-1424. doi: 10.1038/s41589-022-01137-w. Epub 2022 Sep 26.
Anti-CRISPR (Acr) proteins are encoded by phages to inactivate CRISPR-Cas systems of bacteria and archaea and are used to enhance the CRISPR toolbox for genome editing. Here we report the structure and mechanism of AcrIF24, an Acr protein that inhibits the type I-F CRISPR-Cas system from Pseudomonas aeruginosa. AcrIF24 is a homodimer that associates with two copies of the surveillance complex (Csy) and prevents the hybridization between CRISPR RNA and target DNA. Furthermore, AcrIF24 functions as an anti-CRISPR-associated (Aca) protein to repress the transcription of the acrIF23-acrIF24 operon. Alone or in complex with Csy, AcrIF24 is capable of binding to the acrIF23-acrIF24 promoter DNA with nanomolar affinity. The structure of a Csy-AcrIF24-promoter DNA complex at 2.7 Å reveals the mechanism for transcriptional suppression. Our results reveal that AcrIF24 functions as an Acr-Aca fusion protein, and they extend understanding of the diverse mechanisms used by Acr proteins.
抗 CRISPR（Acr）蛋白由噬菌体编码，可使细菌和古菌的 CRISPR-Cas 系统失活，并被用于增强基因组编辑的 CRISPR 工具包。在这里，我们报告了 AcrIF24 的结构和机制，AcrIF24 是一种抑制铜绿假单胞菌 I 型-F CRISPR-Cas 系统的 Acr 蛋白。AcrIF24 是一种同源二聚体，与两个监视复合物（Csy）结合，防止 CRISPR RNA 与靶 DNA 杂交。此外，AcrIF24 作为一种抗 CRISPR 相关（Aca）蛋白，抑制 acrIF23-acrIF24 操纵子的转录。AcrIF24 单独或与 Csy 形成复合物时，能够以纳摩尔亲和力结合到 acrIF23-acrIF24 启动子 DNA 上。在 2.7 Å分辨率下，Csy-AcrIF24-启动子 DNA 复合物的结构揭示了转录抑制的机制。我们的结果表明，AcrIF24 作为一种 Acr-Aca 融合蛋白发挥作用，并且扩展了对 Acr 蛋白使用的不同机制的理解。
