# Evaluating the Potential Inhibition of PP2A by Nodularin-R Disinfection By-Products: Effect and Mechanism

## TL;DR

This study explores how nodularin-R disinfection by-products affect protein phosphatase 2A, revealing structural changes that reduce toxicity but still allow some inhibitory effects.

## Contribution

The study identifies structural changes in Adda3 as key to reduced toxicity and provides a mechanistic explanation for the inhibitory effects of NOD-R-DBPs on PP2A.

## Key findings

- Structural changes in 'Adda3' during chlorination significantly reduce NOD-R toxicity.
- NOD-R-DBPs retain some toxicity (2.8–81% of NOD-R) and affect key interactions with PP2A.
- Disruption of Adda3 alters interactions with PP2A, increasing Mn2+ exposure and promoting phosphate binding.

## Abstract

The secondary contamination of nodularin disinfection by-products (NOD-DBPs) is a problem worthy of attention. In this study, prototypical NOD-R-DBPs were prepared, and their toxicity was assessed using conventional protein phosphatase (PPs) inhibition assay, confirming that structural changes in “Adda3” during chlorination are key factors leading to a significant reduction in NOD-R toxicity. However, some NOD-R-DBPs still exhibit certain levels of toxicity (2.8–81% of NOD-R). To elucidate the mechanism underlying the potential inhibitory effect of NOD-R-DBPs on protein phosphatase 2A (PP2A), molecular simulations were employed to establish interaction models between prototypical NOD-R-DBPs and PP2A using homology modeling strategies, and molecular docking was used to obtain candidate interaction parameters between prototypical NOD-R-DBPs and PP2A. Structural changes in “Adda3” weakened the hydrogen bonds “Adda3”Asn117 and “Adda3”His118. Subsequently, the disruption of “Adda3” altered key interactions between NOD-R-DBPs and PP2A (hydrogen bond Mdhb5 ← Arg89, ionic bond Glu4-Arg89, metal bond His241-Mn12+, etc.). The changes in these interactions further altered the interactions between conserved amino acids and the catalytic center Mn2+ (ionic bond Asp57-Mn22+), thereby increasing Mn2+ exposure. Meanwhile, the retained interactions promoted the binding of -PO4 with the conserved amino acids His118 and Arg89. Prototypical NOD-R-DBPs retained the aforementioned key interactions and thus exhibit potential inhibitory effects on PP2A. The varying degrees of damage to the Adda3 structure led to significant differences in the inhibitory effects of different NOD-R-DBPs on PP2A.