Abstract

The binding mechanisms of two cyanobacterial toxins, Microcystin-LR and Nodularin, to Protein Phosphatase 1 (PP1) were studied with molecular modeling and molecular dynamics simulations. The models of the two toxin-phosphatase complexes are based on the structure of PP1-microcystin complex determined by X-ray crystallography, and on the conformation of nodularin in water determined by NMR. The binding site of PP1 including the ligated toxin and the surrounding water molecules were simulated for 600 ps using CHARMm software. Conformations, dynamics and intermolecular interactions were analyzed from the simulations. The binding was found to be quite similar for both toxins. The characteristic feature in the binding was the interaction of IGlu amino acid carboxyl group of the toxins with the metal ions in the PP1 catalytic site. A number of other interactions in the enzyme and toxins, which participated in the binding, was found as well. The two models of the PP1-inhibitor complexes, presented here, are mostly in agreement with the experimental data, and explain why certain modifications in cyanobacterial hepatotoxins and in protein phosphatases affect the toxin binding.