A methylome-derived m⁶-dAMP trigger assembles a PUA-Cal-HAD immune filament that depletes dNTPs to abort phage...

Area of Science:

• Bacteriology
• Molecular Biology
• Immunology

Background:

• Bacteria possess defense systems against phage infection, but the specific danger signals remain largely unknown.
• Distinguishing self from foreign invaders like phages is crucial for bacterial survival.

Purpose of the Study:

• To identify the danger signals triggering bacterial defense mechanisms against phages.
• To elucidate the molecular mechanism of anti-phage protection conferred by the PUA-Calcineurin-CE-HAD module in *Escherichia coli*.

Main Methods:

• Biochemical assays to study protein-ligand interactions and enzyme kinetics.
• Filament formation assays and characterization of the PUA-Calcineurin-CE-HAD module.
• Analysis of phage-bacteria interactions under different conditions.

Main Results:

• The PUA-Calcineurin-CE-HAD module binds to Dam-methylated deoxyadenosine monophosphate (m⁶-dAMP), a product of phage-induced DNA degradation.
• Ligand binding induces the assembly of a PUA-Calcineurin-CE hexamer into a polymerizing filament.
• This filament functions as a dNTP sink, depleting dATP and dADP, which halts phage replication and causes abortive infection.
• Phages employ DNA mimic proteins to inhibit filament assembly, indicating a direct counter-defense strategy.

Conclusions:

• The PUA-Calcineurin-CE-HAD module provides broad anti-phage protection by sensing m⁶-dAMP and forming a dNTP-depleting filament.
• This mechanism represents a novel nucleotide-depletion antiviral defense strategy in bacteria.
• The findings suggest that modified-nucleotide sensing by related PUA-Calcineurin-CE modules is a widespread bacterial defense mechanism.