Cyclic oligoadenylate signalling mediates Mycobacterium tuberculosis CRISPR defence

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• CRISPR systems provide prokaryotic adaptive immunity against mobile genetic elements (MGE).
• Type III CRISPR systems involve RNA detection, target RNA cleavage, DNA nuclease activation, and cyclic oligoadenylate (cOA) synthesis.
• cOA activates Csx1/Csm6 effectors for non-specific RNA degradation, enhancing bacterial defense.

Purpose of the Study:

• To comprehensively analyze the in vitro and in vivo activities of the type III-A CRISPR system in Mycobacterium tuberculosis.
• To elucidate the primary mechanisms of MGE immunity in M. tuberculosis, focusing on the roles of cA6 signaling and Csm6.
• To investigate the potential for reprogramming type III CRISPR systems by altering effector proteins.

Main Methods:

• In vitro and in vivo assays were performed to study the M. tuberculosis type III-A CRISPR system.
• Analysis included characterization of cyclic and linear oligonucleotide synthesis and effector activities.
• Experiments involved manipulating effector proteins to assess system reprogrammability.

Main Results:

• The M. tuberculosis type III-A CRISPR system primarily relies on a cyclic hexa-adenylate (cA6) signaling pathway and the Csm6 ribonuclease for immunity against MGE.
• DNA cleavage by the HD nuclease domain appears to be a less significant mechanism in this system.
• The study demonstrated that the type III CRISPR system can be reprogrammed by replacing effector proteins, a novel finding with implications for understanding adaptive immunity.

Conclusions:

• Mycobacterium tuberculosis possesses a fully functional type III CRISPR interference system.
• Immunity is predominantly mediated by the cA6-Csm6 pathway, highlighting the importance of cyclic oligonucleotide signaling.
• The reprogrammability of this CRISPR system opens avenues for fundamental research and potential biotechnological applications.