DSSR-PyMOL cartoon-block schematics: PDB entry 6w1x

PDB-id

6w1x; DSSR-derived features in text and JSON formats

Class

immune system-RNA

Method

cryo-EM (3.9 Å)

Summary

cryo-EM structure of anti-crispr acrif9, bound to the type i-f crrna-guided crispr surveillance complex

Reference

Hirschi M, Lu WT, Santiago-Frangos A, Wilkinson R, Golden SM, Davidson AR, Lander GC, Wiedenheft B (2020): "AcrIF9 tethers non-sequence specific dsDNA to the CRISPR RNA-guided surveillance complex." Nat Commun, 11, 2730. doi: 10.1038/s41467-020-16512-1.

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.