Bacterial Toxin Mimics Human CD38 to Deplete NAD+ in Rivals and Host Cells

NAD+ is a universal metabolic currency essential for energy production, DNA repair, and longevity-linked pathways including sirtuins and PARP enzymes. Its depletion is associated with aging and disease, making enzymes that consume NAD+ — like human CD38 — targets of intense longevity research. This study reveals that bacteria have independently evolved, or co-opted, an almost identical enzymatic fold for use as a weapon in microbial warfare.

Working with Pantoea ananatis, a plant-pathogenic bacterium, researchers analyzed a genomic island associated with its Type VI Secretion System (T6SS). They found a specialized PAAR protein (PANA_2924) containing an N-terminal trafficking domain and a C-terminal extension of unknown function. Expression of this C-terminal domain (ARC) in E. coli caused strong growth arrest, and expression in yeast (Saccharomyces cerevisiae) also inhibited growth — demonstrating dual antibacterial and anti-eukaryotic toxicity.

The crystal structure of the ARC domain, solved to 1.6 Å resolution, revealed a globular two-lobed fold consisting of a four-stranded β-sheet capped by five α-helices — nearly identical to human CD38. DALI structural alignment confirmed the similarity (Z-score: 8.6), with key catalytic residues conserved despite only ~26% sequence identity. Biochemical assays confirmed that the bacterial ARC domain hydrolyzes both NAD+ and NADP+ in vitro and in vivo, depleting these critical cofactors in target cells. A small adjacent gene (PANA_2923) encodes a cognate immunity protein that directly binds the toxin in a 1:1 complex, protecting the producing bacterium from self-intoxication.

Comparative genomics showed that CD38-like ARC domains are not unique to Pantoea — they are broadly distributed across bacterial phyla and fused to multiple distinct secretion and delivery systems (T6SS, T7SS, and CDI contact-dependent inhibition systems). Cross-immunity experiments demonstrated that non-cognate toxin–immunity pairs from different bacteria can partially protect against each other, suggesting functional conservation across this toxin class.

For longevity science, these findings carry dual significance. First, they illuminate a natural strategy for NAD+ depletion with atomic-level precision, potentially informing therapeutic targeting of CD38 — already a major focus for NAD+ restoration strategies in aging. Second, they reveal that bacteria harboring these toxins may influence host NAD+ levels during infection or colonization, with potential implications for host metabolism and immunity.