Binding studies for the interaction between hazardous organophosphorus compound phosmet and lysozyme: Spectroscopic and In-silico analyses

Abstract

Organophosphorus compounds are generally toxic compounds found uses in agriculture, pharmaceutics, and other industries. These organophosphorus compounds are life threatening and may cause mortalities on acute exposure. Also, some of these are well known nerve agents. Phosmet is one such organophosphorus compound with moderate nerve toxicity on prolonged exposure. Phosmet is widely used pesticide on various trees including apple, pear, peach, almond and vines like grape vine. Thus, phosmet is the major contaminant of most of the consumed fruits.The present study investigated the binding of phosmet with lysozyme to understand the toxicology and the transport of phosmet using various spectroscopic techniques, molecular modeling and enzymatic assay. The ability of lysozyme to act as a biomarker for phosmet can also be revealed by the current study. The UV–Visible spectrum of lysozyme in presence of phosmet indicated hyperchromicity in the absorbance peak of lysozyme. The fluorescence quenching of lysozyme in presence of phosmet involve predominantly static quenching. The complexation is further quantified in terms of a binding constant (Kb) and the number of sets of equivalent binding sites (n) with the help of double logarithmic regression curve. The Kb value of 103–104 M−1 and n value near 1 indicated that phosmet is binding through non-covalent forces in single set of equivalent binding sites. Static quenching was additionally confirmed by modified Stern-Volmer plot for lysozyme-phosmet interactions. Post binding protein conformation changes and the enhanced protein stability of lysozyme were showed by CD spectrum and melting curves of lysozyme. The FT-IR spectrum also revealed the changes in secondary structure content of protein on interaction with phosmet. The docked structure for binding of phosmet with lysozyme were achieved using molecular docking analysis with a glide score −5.273 k J/mol-1 that indicated towards moderate binding as suggested by other experimental studies. The enzymatic activity of lysozyme depicted an increase of 16% after binding with phosmet indicative of interaction with the active site.