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SAM-AMP lyases in type III CRISPR defence.

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Type III CRISPR systems utilize SAM-AMP signaling for phage defense. Researchers elucidated the structure and function of Clostridium botulinum SAM-AMP lyase, revealing its anti-CRISPR potential.

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Area of Science:

  • Microbiology
  • Molecular Biology
  • Biochemistry

Background:

  • Type III CRISPR systems use Cas10 to generate second messengers for effector activation.
  • While cyclic oligoadenylate is common, SAM-AMP is an alternative signaling molecule.
  • SAM-AMP activates CorA-like effectors for anti-phage defense, requiring degradation by enzymes like NrN.

Purpose of the Study:

  • To investigate the structure and activity of Clostridium botulinum SAM-AMP lyase.
  • To determine if C. botulinum SAM-AMP lyase can substitute for NrN in providing immunity.
  • To understand the mechanism of SAM-AMP degradation by this enzyme.

Main Methods:

  • X-ray crystallography to determine the structure of C. botulinum SAM-AMP lyase.
  • Biochemical assays to assess enzyme activity and substrate turnover.
  • Bioinformatic analysis to identify related enzymes, including phage-encoded lyases.

Main Results:

  • The structure of C. botulinum SAM-AMP lyase bound to 5'-methylthioadenosine-AMP was determined.
  • The enzyme efficiently degrades SAM-AMP and can confer CorA-mediated immunity in E. coli.
  • A phage-encoded SAM-AMP lyase was identified with efficient in vitro SAM-AMP degradation activity.

Conclusions:

  • C. botulinum SAM-AMP lyase is a functional phosphodiesterase that degrades SAM-AMP, contributing to CRISPR-mediated immunity.
  • This lyase can replace the function of NrN, highlighting functional conservation in anti-phage defense mechanisms.
  • The discovery of a phage-encoded SAM-AMP lyase suggests a potential anti-CRISPR mechanism targeting this signaling pathway.