Computational and biochemical characterization of the immobilized esterase of Salinicoccus roseus for pesticide degradation

The continuous exposure of chemical pesticides in agriculture, their contamination in soil and water pose serious threat to the environment. Current study used an approach to evaluate various pesticides like Hexaconazole, Mancozeb, Pretilachlor, Organophosphate and λ-cyhalothrin degradation capability of esterase. The enzyme was isolated from Salinicoccus roseus. Genome analysis unveiled the carboxylesterase genes underlying the degradation of pesticides, and was located between 2070Mbp to 2080Mbp region. Herein, partially purified esterase was immobilized into beads by mixing with an equal volume (1:1) of sodium alginate solution [2.5% (w/v)].Scanning electron microscopy (SEM) of the beads showed the microspheres for enhanced enzyme-substrate reaction, wide peak at 3316, 1635 and 696 cm^{- 1} in Fourier-transform infrared spectroscopy (FTIR) represented intermolecular hydrogen bonding, and thermogravimetric analysis (TGA) reaffirmed the binding of esterase entrapped into the beads. Maximum degradation rate (after 4 days) for free enzyme accounted 83.2% in Hexaconazole. Degradation rate moderately increased 4% in the presence of immobilized esterase. Degradation products were detected by liquid chromatography-mass spectrometry (LC-MS). Cytotoxicity test (root length and mitotic index) revealed differences in various treatments. Enzyme kinetics parameters, Michaëlis-Menten constant (K_M) 6.61 mM and maximum velocity (V_max) 1.89 µmol/min/mg increased after immobilization. Further, molecular docking results validated that esterase contributed to pesticide degradation by catalytic triad of Ser⁹³-His²²²-Phe²⁴, ligand interactions, and specific binding pockets. Additionally, molecular dynamics (MD) simulations confirmed the protein-ligand conformational stability. Hence, present study highlighted an effective method for improving the catalytic properties of esterase, and also potential candidate for bioremediation of pesticides.