A processed noncoding RNA regulates an altruistic bacterial antiviral system.

Area of Science:

• Microbiology
• Structural Biology
• Molecular Biology

Background:

• Bacteriophages drive bacterial evolution, necessitating phage-resistance mechanisms.
• The ToxIN system, comprising ToxN toxin and ToxI antitoxin, confers phage resistance.
• The precise mechanisms of ToxN toxicity and ToxI inhibition remain undefined.

Purpose of the Study:

• To determine the structural basis of the ToxN-ToxI complex.
• To elucidate the mechanism of phage resistance mediated by the ToxIN system.

Main Methods:

• X-ray crystallography was employed to determine the structure of the ToxN-ToxI complex.
• Structural analysis focused on RNA-protein interactions within the complex.

Main Results:

• The crystal structure of the ToxN-ToxI complex from Pectobacterium atrosepticum was determined at 2.75-Å resolution.
• A trimeric complex formed by three ToxI monomers and three ToxN monomers was observed.
• Extensive RNA-protein interactions mediate the assembly of the ToxN-ToxI complex.
• ToxN was identified as an endoRNase that processes ToxI, with regulation by its catalytic product.

Conclusions:

• The structure reveals intricate RNA-protein interactions critical for ToxIN system assembly.
• ToxN functions as an endoRNase, processing its own regulatory RNA antitoxin, ToxI.
• This provides mechanistic insight into bacterial phage resistance strategies.