English abstract
2,2-bis(4-hydroxyphenyl) propane, often known as bisphenol A (BPA), is an organic substance that is made by combining acetone and phenol and is used to make epoxy resins and polycarbonate plastics. Epoxy resins are used to coat metal can surfaces that are in contact with foods and beverages. BPA is considered as an endocrine disruptor which can exhibits estrogenic activity [1]. BPA can migrate from cans and polycarbonate plastics to foods. In a recent study, it was shown that 0.5 mg/kg of BPA may migrate from food packaging to its contents [2]. Studies have shown that BPA can cause adverse health effects such as an increase in insulin resistance, obesity, diabetes, and infertility in men. Furthermore, studies on BPA exposure verify that, of all sources and across all population groups, diet is the most important exposure source. Milk products are considered one of the widely consumed products by infants, children, and adults. Milk contains two main kinds of proteins. Casein makes up 80% of the proteins found in milk, whereas whey makes up 20%. Recent scientific attention has been focused on BPA's interactions with certain proteins to better understand the toxicity mechanism. Therefore, in this study, our intention is to provide investigation on the interaction of BPA with the two milk proteins by molecular modeling and electronic spectroscopy such as UV-visible absorption spectroscopy (UVA) and fluorescence spectroscopy (FL). In order to determine the optimum conditions to conduct the interaction experiments, the pH and concentration dependence on the FL emission and UVA spectra of these molecules are studied first. By estimating the binding constant, the level of toxicity of BPA is determined. Further the type of molecular interaction between the molecules is evaluated through analyzing the Stern-Volmer plots. In order to gain deeper insight on the complexation process of BPA with the proteins, we have conducted molecular dynamics (MD) simulations on these systems. Our results indicate that the BPA molecules prefer to bind to the proteins within the pockets dominantly made by tryptophan (TRP) residues, which is in agreement with our spectroscopy measurements. We further analyze the factors contributing to stability of the complex between BPA and proteins which are root mean square deviation (RMSD), root means square fluctuation (RMSF), radius of gyration (š¯‘…š¯‘”), solvent accessible surface area (SASA), and
Ramachandran plot. The results showed that the conformational changes introduced by the addition of BPA in casein protein are higher than that for whey protein. Our results are key to the designing of package materials and conditions to store the milk in liquid form. FÓ§rster energy transfer analyses were done. The intermolecular distance between the donor and the acceptor was calculated to be 1.3 nm which is near to 0.8 nm of TYR calculated by MD simulation.
