Molecular modeling and docking of recombinant HAP-phytase of a thermophilic mould Sporotrichum thermophile reveals insights into molecular catalysis and biochemical properties.

A thermostable and protease-resistant HAP-phytase of Sporotrichum thermophile was over-expressed in Pichia pastoris X-33. Purified recombinant phytase displayed all its biochemical properties similar to wild type. Molecular modeling and docking of phytase with various substrates showed differential binding patterns with GoldScore values ranging from 40.61 to 79.78. Docking with different substrates revealed strong binding affinity with ATP and phytic acid, while the lowest with AMP and phosphoenol pyruvate. This was further confirmed using biochemical assays, as the recombinant enzyme displayed broad substrate specificity. Docking with inhibitors also showed differential binding with GoldScore values ranging from 22.94 (2,3-butanedione) to 85.72 (myo-inositol hexasulphate). Validation using biochemical analysis revealed that both 2,3-butanedione and phenyl glyoxal inhibited the phytase activity significantly. Furthermore, presence of inorganic phosphate in the reaction mixture also inhibited the phytase activity, as there was no activity at and beyond 0.8 mM. Docking of phytase with metavanadate showed binding at the same atom in the active-site where the substrate i.e. phytic acid binds. Vanadium incorporation resulted in the catalytic conversion of phytase into a peroxidase with concomitant inhibition of phytase activity. Peroxidase activity was high in acidic range and the product formation showed correlation with reaction time. Furthermore, molecular modeling and docking of recombinant HAP-phytase of a thermophilic mould S. thermophile reveals insights into molecular catalysis that is validated by the biochemical properties.