Prokaryotes have a wide range of antiviral strategies to defend against invading mobile genetic elements (MGEs). Type III CRISPR-Cas systems typically synthesise cyclic oligoadenylate (cOA) second messengers upon binding to cognate foreign RNA. These second messengers allosterically activate type III CRISPR ancillary proteins, potentiating a powerful immune response. Following the discovery of cOA signalling pathway, several ancillary proteins from Csx1/Csm6 family had been described. They sense cOA molecules with their CARF (CRISPR associated Rossman fold) domains and non-specifically cleave RNA with their effector domains. Here, we describe the structure and mechanism of two novel ancillary proteins Can1 and Can2. Can1 has a unique monomeric architecture that contains two CARF domains, a PD-(D/E)XK nuclease domain and a nuclease-like domain. It favours nicking scDNA in the presence of cyclic tetra-adenylate (cA₄) and metal ions. Can2 forms a canonical homodimer and each monomer contains a CARF domain and a PD-(D/E)XK nuclease domain. It exhibits both DNase and RNase activity in the presence of cA₄ and metal ions. It also provides effective immunity against plasmid and bacteriophage infection in a recombinant type III CRISPR-Cas system.
Date of Award | 15 Jun 2022 |
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Original language | English |
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Awarding Institution | |
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Supervisor | Malcolm White (Supervisor) |
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- CRISPR
- Cyclic oligoadenylate
- CARF
- Nuclease
- Antiviral strategy
Structure and mechanism of two type III CRISPR defence nucleases activated by cyclic oligoadenylate
Zhu, W. (Author). 15 Jun 2022
Student thesis: Doctoral Thesis (PhD)