Effect of Divalent Metal Ions on the Ribonuclease Activity of the Toxin Molecule HP0894 from .

Bacteria and archaea respond and adapt to environmental stress conditions by modulating the toxin-antitoxin (TA) system for survival. Within the bacterium , the protein HP0894 is a key player in the HP0894-HP0895 TA system, in which HP0894 serves as a toxin and HP0895 as an antitoxin. HP0894 has intrinsic ribonuclease (RNase) activity that regulates gene expression and translation, significantly influencing bacterial physiology and survival. This activity is influenced by the presence of metal ions such as Mg. In this study, we explore the metal-dependent RNase activity of HP0894. Surprisingly, all tested metal ions lead to a reduction in RNase activity, with zinc ions (Zn) causing the most significant decrease. The secondary structure of HP0894 remained largely unaffected by Zn binding, whereas structural rigidity was notably increased, as revealed using CD analysis. NMR characterized the Zn binding, implicating numerous His, Asp, and Glu residues in HP0894. In summary, these results suggest that metal ions play a regulatory role in the RNase activity of HP0894, contributing to maintaining the toxin molecule in an inactive state under normal conditions.