Insight into the Molecular Mechanism for the Discrepant Inhibition of Microcystins (MCLR, LA, LF, LW, LY) on Protein Phosphatase 2A

Abstract

Microcystins (MCs) exhibit diversified inhibition effects on protein phosphatases (PPs) due to their structural differences. To fully evaluate the potential mechanism for the discrepant inhibition effects, the five most frequent MCs with varying residues at position Z4 were selected as the tested toxins. Their inhibition sequence on PP2A was detected as follows: MCLR > MCLW > MCLA > MCLF > MCLY. Combined with homology modeling and molecular docking technology, the major interaction parameters between the MCs and PP2A were obtained. The correlation analysis for the major interaction parameters and inhibition effects showed that the hydrophobicity of Z4 had an important influence on the interaction of the MCs to PP2A. The introduction of hydrophobic Z4 directly weakened hydrogen bonds Z4→Pro213 and Z4←Arg214, indirectly weakened hydrogen bonds Adda5←Asn117, Glu6←Arg89, and MeAsp3←Arg89, but indirectly enhanced ionic bonds Glu6←Arg89, Glu6-Mn12+, and Glu6-Mn22+. In this way, the combination of the MCs with PP2A was blocked, and thus, the interactions between PP2A and the Mn2+ ions (in the catalytic center) were further affected; metal bonds Asp85-Mn12+ and Asp85-Mn22+ were weakened, while metal bond His241-Mn12+ was enhanced. As a result, the interactions in the catalytic center were inhibited to varying degrees, resulting in the reduced toxicity of MCs.

Regulation Effectiveness and Mechanism of Biotransformation Pathway on the Toxicity of Microcystin-LR Target to Protein Phosphatase 2A

“…Since the Mn 2+ ions in the catalytic center were important to maintain PPs' activity [30], the key interactions involving the Mn 1 2+ ion in the biotransformation pathway were critical for the recovery of the PP2A's catalytic activity. This finding agreed with previous studies, in which the inhibition effects of toxins on PP2A were primarily mediated by Mn 1 2+ ions [25]. Among the structural units of the MCLR/MCLR-BTPs, "Mdha 7 " was more significant than that of other sites.…”

“…To ensure the comparability of MCLR-BTPs with their original toxin, "template dock" mode was adopted (in "template dock" mode, the placement and refinement of MCLR-BTPs were in keeping with their original toxin). The specific docking parameters were set as follows: amber 10 EHT, solvation r-field, temperature 25.0 • C, pH 7.4, salinity 0.05 M [25]. Finally, the candidate interaction parameters (combination areas, related surface areas, hydrogen bonds, metal bonds, ionic bonds, exposure areas of Mn 2+ ions, and introduced phosphate group) related to the combination of toxins to PP2A could be obtained.…”

“…Unfortunately, limited by the crystal structures of MC-BTP-PP complexes, the molecular mechanism of the biotransformation pathway is difficult to elucidate. A pioneering study by Xu et al provided a new perspective on evaluating the interactions between toxins and proteins without corresponding crystal structures [25]. They constructed the interaction models for typical MC-PP2A complexes and explored the key interactions based on homology modeling and molecular docking.…”