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.
Highlights
Bacteria have evolved sophisticated adaptive immune systems, called clustered regularly interspaced short palindromic repeat (CRISPR)-Cas, that provide sequence-specific protection against phage infection
We show that anti-CRISPR protein IF9 (AcrIF9) inhibits the CRISPR-derived RNAs (crRNA)-guided surveillance complex (Csy) by sterically blocking the hybridization of target DNA to the crRNA guide
In order to determine the mechanism of immune suppression by AcrIF9, we co-expressed and purified the Csy with AcrIF9 and determined the structure using cryo-electron microscopy at a nominal resolution of ~3.9Å (Fig. 1, Supplementary Fig. 1, and Supplementary Table 1)
Summary
Bacteria have evolved sophisticated adaptive immune systems, called CRISPR-Cas, that provide sequence-specific protection against phage infection. In addition to sterically blocking the hybridization of complementary dsDNA to the CRISPR RNA, our results show that AcrIF9 binding 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. AcrIF9 bound to Csy, promotes non-specific interactions with dsDNA, potentially sequestering the surveillance complex away from target DNA and thereby providing an additional layer of immune suppression
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
