Tetramerisation of the CRISPR ring nuclease Crn3/Csx3 facilitates cyclic oligoadenylate cleavage
| Autor: | Stuart McQuarrie, Shirley Graham, Malcolm F. White, Sabine Grüschow, Tracey M. Gloster, Januka S Athukoralage |
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| Přispěvatelé: | BBSRC, The Wellcome Trust, University of St Andrews. School of Biology, University of St Andrews. Biomedical Sciences Research Complex |
| Rok vydání: | 2020 |
| Předmět: |
Models
Molecular cooperative enzyme QH301 Biology Cyclic tetra-adenylate CRISPR-Associated Proteins CARF domain Oligonucleotides archaeoglobus fulgidus Second Messenger Systems 0302 clinical medicine Catalytic Domain CRISPR QD Clustered Regularly Interspaced Short Palindromic Repeats Biology (General) R2C 0303 health sciences biology Chemistry General Neuroscience Csx3 General Medicine Cell biology Second messenger system Methanosarcina Medicine BDC Signal Transduction Research Article QH301-705.5 Protein subunit Science Neuroscience(all) Cleavage (embryo) Cyclase General Biochemistry Genetics and Molecular Biology Catalysis 03 medical and health sciences QH301 Ribonucleases Biochemistry and Chemical Biology Immunology and Microbiology(all) Escherichia coli 030304 developmental biology Nuclease General Immunology and Microbiology Biochemistry Genetics and Molecular Biology(all) RNA DAS CARF QD Chemistry Endonucleases cyclic tetra-adenylate Kinetics Nucleic acid biology.protein Other Ring nuclease Protein Multimerization 030217 neurology & neurosurgery |
| Zdroj: | eLife eLife, Vol 9 (2020) |
| ISSN: | 2050-084X |
| Popis: | Type III CRISPR systems detect foreign RNA and activate the cyclase domain of the Cas10 subunit, generating cyclic oligoadenylate (cOA) molecules that act as a second messenger to signal infection, activating nucleases that degrade the nucleic acid of both invader and host. This can lead to dormancy or cell death; to avoid this, cells need a way to remove cOA from the cell once a viral infection has been defeated. Enzymes specialised for this task are known as ring nucleases, but are limited in their distribution. Here, we demonstrate that the widespread CRISPR associated protein Csx3, previously described as an RNA deadenylase, is a ring nuclease that rapidly degrades cyclic tetra-adenylate (cA4). The enzyme has an unusual cooperative reaction mechanism involving an active site that spans the interface between two dimers, sandwiching the cA4 substrate. We propose the name Crn3 (CRISPR associated ring nuclease 3) for the Csx3 family. eLife digest Bacteria protect themselves from infections using a system called CRISPR-Cas, which helps the cells to detect and destroy invading threats. The type III CRISPR-Cas system, in particular, is one of the most widespread and efficient at killing viruses. When a bacterium is infected, the CRISPR-Cas system takes a fragment of the genetic material of the virus, and copies it into a molecule. These molecular ‘police mugshots’ are then loaded into a complex of Cas proteins that patrol the cell, looking for a match and destroying any virus that can be identified. Some Cas proteins also produce alarm signals, called cyclic oligoadenylates (cOAs), which can trigger additional defences. However, this process can damage the genetic material of the bacterium, harming or even killing the cell. Enzymes known as ring nucleases can promptly degrade cOAs and turn off this defence system before it causes harm. However, ring nucleases have only been found in a few species to date; how most bacteria deal with cOA toxicity has remained unknown. Here, Athukoralage et al. set out to determine whether a widespread enzyme known as Csx3, which is often associated with type III CRISPR-Cas systems, could be an alternative off switch for cOA triggered defences. Initial ‘test tube’ experiments with purified Csx3 proteins confirmed that the enzyme could indeed break down cOAs. A careful dissection of Csx3’s molecular structure, using biochemical and biophysical techniques, revealed that it worked by ‘sandwiching’ a cOA molecule between two co-operating portions of the enzyme. As a final test, Csx3 was introduced into strains of bacteria genetically engineered to have a fully functional Type III CRISPR-Cas system. In these cells, Csx3 successfully turned off the Type III immune response. These results reveal a new way that bacteria avoid the toxic side effects of their own immune defences. Ultimately, this could pave the way for the development of anti-bacterial drugs that work by blocking Csx3 or similar proteins. |
| Databáze: | OpenAIRE |
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