Fuse to defuse : a self-limiting ribonuclease-ring nuclease fusion for type III CRISPR defence
Abstract
Type III CRISPR systems synthesise cyclic oligoadenylate (cOA) second messengers in response to viral infection of bacteria and archaea, potentiating an immune response by binding and activating ancillary effector nucleases such as Csx1. As these effectors are not specific for invading nucleic acids, a prolonged activation can result in cell dormancy or death. Some archaeal species encode a specialised ring nuclease enzyme (Crn1) to degrade cyclic tetra-adenylate (cA4) and deactivate the ancillary nucleases. Some archaeal viruses and bacteriophage encode a potent ring nuclease anti-CRISPR, AcrIII-1, to rapidly degrade cA4 and neutralise immunity. Homologues of this enzyme (named Crn2) exist in type III CRISPR systems but are uncharacterised. Here we describe an unusual fusion between cA4-activated CRISPR ribonuclease (Csx1) and a cA4-degrading ring nuclease (Crn2) from Marinitoga piezophila. The protein has two binding sites that compete for the cA4 ligand, a canonical cA4-activated ribonuclease activity in the Csx1 domain and a potent cA4 ring nuclease activity in the C-terminal Crn2 domain. The cA4 binding affinities and activities of the two constituent enzymes in the fusion protein may have evolved to ensure a robust but time-limited cOA-activated ribonuclease activity that is finely tuned to cA4 levels as a second messenger of infection.
Citation
Samolygo , A , Athukoralage , J S , Graham , S & White , M 2020 , ' Fuse to defuse : a self-limiting ribonuclease-ring nuclease fusion for type III CRISPR defence ' , Nucleic Acids Research , vol. 48 , no. 11 , pp. 6149–6156 . https://doi.org/10.1093/nar/gkaa298
Publication
Nucleic Acids Research
Status
Peer reviewed
ISSN
0305-1048Type
Journal article
Rights
Copyright © The Author(s) 2020. Published by Oxford University Press on behalf of Nucleic Acids Research. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
Description
Funding: Biotechnology and Biological Sciences Research Council [REF BB/S000313/1 to M.F.W.]; Funding for open access charge: RCUK block grant.Collections
Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.