Phage-encoded NARP3 system rebuilds NAD⁺ to subvert bacterial immunity

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Bacteriophages (phages) employ various strategies to counteract bacterial immunity, particularly those targeting nicotinamide adenine dinucleotide (NAD+).
• Existing known phage countermeasures include NAD+ reconstitution pathway 1 (NARP1) and NARP2, which manage NAD+ levels through different biochemical routes.
• The existence of additional NAD+-restoring strategies in phages remained largely unexplored.

Purpose of the Study:

• To identify and characterize novel NAD+-restoring phage pathways.
• To elucidate the mechanism of action and structural basis of the newly discovered pathway.
• To understand the role of this pathway in phage-bacterial conflicts and its biotechnological potential.

Main Methods:

• Bioinformatic analysis to identify conserved gene clusters in phages.
• Biochemical assays to determine enzyme activity and substrate specificity.
• X-ray crystallography to determine the structure of key enzymes.
• Site-directed mutagenesis to confirm the essentiality of pathway components.

Main Results:

• Identification of NARP3, a conserved two-gene pathway widespread in Enterobacteriaceae-infecting phages.
• NARP3 comprises a nicotinamide riboside transporter (Bas30_87) and a bifunctional enzyme (Bas30_86) that converts nicotinamide riboside to NAD+.
• NARP3 effectively restores NAD+ pools depleted by bacterial defenses, enabling robust phage replication.
• X-ray crystal structures revealed the mechanism of NAD+ synthesis and regulation by Bas30_86.

Conclusions:

• NARP3 represents a novel metabolite-centered countermeasure employed by phages to overcome bacterial NAD+-directed immunity.
• The discovery expands the known repertoire of phage survival strategies and highlights NAD+ metabolism as a critical battleground.
• NARP3 provides a framework for engineering phages to bypass bacterial immunity and offers insights for biotechnological applications harnessing viral strategies.