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 "Adda(3)" 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 "Adda(3)" weakened the hydrogen bonds "Adda(3)"Asn(117) and "Adda(3)"His(118). Subsequently, the disruption of "Adda(3)" altered key interactions between NOD-R-DBPs and PP2A (hydrogen bond Mdhb(5) ← Arg(89), ionic bond Glu(4)-Arg(89), metal bond His(241)-Mn(1)(2+), etc.). The changes in these interactions further altered the interactions between conserved amino acids and the catalytic center Mn(2+) (ionic bond Asp(57)-Mn(2)(2+)), thereby increasing Mn(2+) exposure. Meanwhile, the retained interactions promoted the binding of -PO(4) with the conserved amino acids His(118) and Arg(89). Prototypical NOD-R-DBPs retained the aforementioned key interactions and thus exhibit potential inhibitory effects on PP2A. The varying degrees of damage to the Adda(3) structure led to significant differences in the inhibitory effects of different NOD-R-DBPs on PP2A.