A Type III CRISPR Ancillary Ribonuclease Degrades Its Cyclic Oligoadenylate Activator.
J Mol Biol 2019;
431:2894-2899. [PMID:
31071326 PMCID:
PMC6599890 DOI:
10.1016/j.jmb.2019.04.041]
[Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2019] [Revised: 04/22/2019] [Accepted: 04/29/2019] [Indexed: 12/26/2022]
Abstract
Cyclic oligoadenylate (cOA) secondary messengers are generated by type III CRISPR systems in response to viral infection. cOA allosterically activates the CRISPR ancillary ribonucleases Csx1/Csm6, which degrade RNA non-specifically using a HEPN (Higher Eukaryotes and Prokaryotes, Nucleotide binding) active site. This provides effective immunity but can also lead to growth arrest in infected cells, necessitating a means to deactivate the ribonuclease once viral infection has been cleared. In the crenarchaea, dedicated ring nucleases degrade cA4 (cOA consisting of 4 AMP units), but the equivalent enzyme has not been identified in bacteria. We demonstrate that, in Thermus thermophilus HB8, the uncharacterized protein TTHB144 is a cA4-activated HEPN ribonuclease that also degrades its activator. TTHB144 binds and degrades cA4 at an N-terminal CARF (CRISPR-associated Rossman fold) domain. The two activities can be separated by site-directed mutagenesis. TTHB144 is thus the first example of a self-limiting CRISPR ribonuclease.
TTHB144 is a cyclic tetra-adenylate activated ribonuclease.
TTHB144 degrades cyclic tetra-adenylate at its CARF domain.
Self-limiting enzymes like TTHB144 may regulate anti-viral signaling in bacteria.
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