SNAP output for PDB entry 6o6v [SNAP web server]

PDB-id

6o6v; SNAP-derived features in text and JSON formats; DNAproDB

Class

immune system-RNA

Method

X-ray (2.35 Å)

Summary

Crystal structure of csm6 in complex with ca4 by soaking ca4 into csm6

Reference

Jia N, Jones R, Yang G, Ouerfelli O, Patel DJ (2019): "CRISPR-Cas III-A Csm6 CARF Domain Is a Ring Nuclease Triggering Stepwise cA4Cleavage with ApA>p Formation Terminating RNase Activity." Mol.Cell, 75, 944-956.e6. doi: 10.1016/j.molcel.2019.06.014.

Abstract

Type III-A CRISPR-Cas surveillance complexes containing multi-subunit Csm effector, guide, and target RNAs exhibit multiple activities, including formation of cyclic-oligoadenylates (cA_n) from ATP and subsequent cA_n-mediated cleavage of single-strand RNA (ssRNA) by the trans-acting Csm6 RNase. Our structure-function studies have focused on Thermococcus onnurineus Csm6 to deduce mechanistic insights into how cA₄ binding to the Csm6 CARF domain triggers the RNase activity of the Csm6 HEPN domain and what factors contribute to regulation of RNA cleavage activity. We demonstrate that the Csm6 CARF domain is a ring nuclease, whereby bound cA₄ is stepwise cleaved initially to ApApApA>p and subsequently to ApA>p in its CARF domain-binding pocket, with such cleavage bursts using a timer mechanism to regulate the RNase activity of the Csm6 HEPN domain. In addition, we establish T. onnurineus Csm6 as an adenosine-specific RNase and identify a histidine in the cA₄ CARF-binding pocket involved in autoinhibitory regulation of RNase activity.