Coupling of ssRNA cleavage with DNase activity in type III-A CRISPR-Csm revealed by cryo-EM and biochemistry

• DOI: 10.1038/s41422-019-0151-x
• Publication Date: 2019-02-27T11:16:50Z
• Authors: Minghui Guo; Kaiming Zhang; Yuwei Zhu; Grigore D. Pintilie; Xiaoyu Guan; Shanshan Li; Michael F. Schmid; Zhuo Ma; Wah Chiu; Zhiwei Huang
• Keywords: Trans-activating crRNA; Cleavage (geology)

The type III CRISPR-Cas (clustered regularly interspaced short palindromic repeats-CRISPR-associated genes) systems are bacterially encoded adaptive immune for defense against invading nucleic acids. They accomplish this task through the coordinated cleavage of substrates single-stranded RNA and DNA (ssDNA ssRNA) by Csm (type III-A) or Cmr III-B) effector complexes. ssRNA is complementarily bound to CRISPR (crRNA). However, structural basis DNase RNase activation nucleoprotein complex largely unknown. Here we report cryo-EM structures Csm-crRNA complex, with without target ssRNA, at near-atomic resolution. Our maps allow us build atomic models key macromolecular components, including Cas10, Csm2, Csm3, Csm4, crRNA ssRNA. structure resolves unambiguously stoichiometry tertiary protein interactions between components crRNA/ssRNA. Interestingly, new proteins presented here similar those previously known in other species despite their low sequence similarity. combined biochemical data suggest that preferentially carried out near its 5'-end, extent among regulates activity 3' flanking activates Cas10 allosterically.