# Molecular determinants of nucleic acid recognition by an RNA-targeting ADP-ribosyltransferase toxin

## TL;DR

This paper explores how a bacterial toxin called RhsP2 specifically targets RNA molecules, revealing the molecular mechanisms behind its antibacterial function.

## Contribution

The study identifies a positively charged RNA-binding surface on RhsP2 that is crucial for RNA recognition and toxin activity.

## Key findings

- RhsP2 recognizes RNA substrates via a positively charged surface near its catalytic site.
- Mutations in this RNA-binding surface disrupt RNA binding and ADP-ribosylation activity.
- RhsP2 binds small regulatory RNAs with varying affinities, indicating shape and electrostatic interactions are important for target selection.

## Abstract

ADP-ribosyltransferases use NAD+ to catalyze ADP-ribosylation reactions that regulate diverse cellular pathways in eukaryotes or function as toxins delivered by bacteria to kill competitor or host cells. Although most characterized ARTs target proteins, we recently identified RhsP2 as an antibacterial ART toxin that modifies the 2′-OH groups of structured RNAs during bacterial competition. However, the molecular basis for RhsP2’s unique specificity toward RNA remains poorly understood. Here, we show that RhsP2 is a divergent member of the ART superfamily that recognizes nucleic acid substrates via a positively charged RNA-binding surface adjacent to its catalytic site. Mutations within this surface disrupt both RNA binding and ADP-ribosylation activity, abolishing RhsP2’s antibacterial function. We further demonstrate that RhsP2 binds distinct small regulatory RNAs with varying affinities, suggesting that both electrostatic interactions and shape complementarity contribute to RNA target selection. Together, our findings define the molecular determinants of nucleic acid recognition by an unusual RNA-targeting ART toxin.