Using Cryoem to Understand How Phages Evade Bacterial CRISPR Defense System
- Chowdhury, Saikat [ Int Struct and Comp Biol, The Scripps Research Institute, La Jolla, CA, USA ]
- Rollins, MaryClare F. [ Montana State University: Microbiology & Cell Biology ]
- Carter, Joshua [ Montana State University: Microbiology & Cell Biology ]
- Jackson, Ryan [ Montana State University: Microbiology & Cell Biology ]
- Nosaka, Lyn'Al [ Int Struct and Comp Biol, The Scripps Research Institute, La Jolla, CA, USA ]
- Wiedenheft, Blake [ Montana State University: Microbiology & Cell Biology ]
- Lander, Gabriel C. [ Int Struct and Comp Biol, The Scripps Research Institute, La Jolla, CA, USA ]
Bacteria and archaea have evolved different CRISPR based adaptive immune system for defense against phage infections. Pseudomonas aeruginosa has type I-F CRISPR-cas defense system, where the cas-crRNA surveillance complex (csy-complex) binds to foreign DNA and recruits the cas-2/3 nuclease for degradation of the foreign DNA. Bacteriophages have evolved mechanisms of evading this CRISPR defense system by encoding different anti-CRISPR (ACR) proteins. ACR1F and ACR2F are two such ACRs that bind to specific regions of the csy-complex and suppress the immune system. We present here a 3.4Ã… cryo-EM reconstruction of the ACR-bound csy-complex. This structure not only shows the overall organization of the type I-F csy-complex, but also reveals how ACRs interact with this complex and prevent the binding of phage DNA.