AcrIF9 tethers non-sequence specific dsDNA to the CRISPR RNA-guided surveillance complex
Marscha Hirschi, Wangting Lu, Andrew Santiago‐Frangos, Royce A. Wilkinson, Sarah Golden, Alan R. Davidson, Gabriel C. Lander, Blake Wiedenheft
Abstract
Bacteria have evolved sophisticated adaptive immune systems, called CRISPR-Cas, that provide sequence-specific protection against phage infection. In turn, phages have evolved a broad spectrum of anti-CRISPRs that suppress these immune systems. Here we report structures of anti-CRISPR protein IF9 (AcrIF9) in complex with the type I-F CRISPR RNA-guided surveillance complex (Csy). In addition to sterically blocking the hybridization of complementary dsDNA to the CRISPR RNA, our results show that AcrIF9 binding also promotes non-sequence-specific engagement with dsDNA, potentially sequestering the complex from target DNA. These findings highlight the versatility of anti-CRISPR mechanisms utilized by phages to suppress CRISPR-mediated immune systems.