SNAP output for PDB entry 6muu [SNAP web server]

PDB-id

6muu; SNAP-derived features in text and JSON formats; DNAproDB

Class

RNA binding protein-RNA

Method

cryo-EM (3.0 Å)

Summary

cryo-EM structure of csm-crrna binary complex in type iii-a crispr-cas system

Reference

Jia N, Mo CY, Wang C, Eng ET, Marraffini LA, Patel DJ (2019): "Type III-A CRISPR-Cas Csm Complexes: Assembly, Periodic RNA Cleavage, DNase Activity Regulation, and Autoimmunity." Mol. Cell, 73, 264. doi: 10.1016/j.molcel.2018.11.007.

Abstract

Type ΙΙΙ CRISPR-Cas systems provide robust immunity against foreign RNA and DNA by sequence-specific RNase and target RNA-activated sequence-nonspecific DNase and RNase activities. We report on cryo-EM structures of Thermococcus onnurineus Csm_crRNA binary, Csm_crRNA-target RNA and Csm_crRNA-target RNA_anti-tag ternary complexes in the 3.1 Å range. The topological features of the crRNA 5'-repeat tag explains the 5'-ruler mechanism for defining target cleavage sites, with accessibility of positions -2 to -5 within the 5'-repeat serving as sensors for avoidance of autoimmunity. The Csm3 thumb elements introduce periodic kinks in the crRNA-target RNA duplex, facilitating cleavage of the target RNA with 6-nt periodicity. Key Glu residues within a Csm1 loop segment of Csm_crRNA adopt a proposed autoinhibitory conformation suggestive of DNase activity regulation. These structural findings, complemented by mutational studies of key intermolecular contacts, provide insights into Csm_crRNA complex assembly, mechanisms underlying RNA targeting and site-specific periodic cleavage, regulation of DNase cleavage activity, and autoimmunity suppression.