The Studies Of Interaction Between Several Typical Endocrine Disruptors And Human Serum Albumin

With the development of science and technology, a large amount of chemical substances are produced and used, which promote the progress of human civilization, but also bring serious pollution problems. The residues of these harmful substances in environment could enter into the body by means of ingestion, inhalation or skin contact, and interact with biomacromolecules such as protein, enzyme and nucleic acid directly or indirectly and then affect their function or genetic characteristic. Considering physiological importance of human serum albumin (HSA), investigating the binding mechanism of toxic materials with HSA has been an interesting research field of life sciences, chemistry and environmental sciences. Based on the significance of toxic substances-protein interactions and research trends at home and abroad, the binding mode and the molecule model of bisphenol A, three phthalate esters and two alkylphenols endocrine disruptors with HSA were revealed by the molecular modeling method, which can predict the possibility of interactions of the endocrine disruptors and HSA theoretically; Fluorescence spectrum, UV absorption spectrum, fourier transform infrared (FT-IR) spectrum and circular dichroism (CD) spectrum were used to study the interactions of the endocrine disruptors with HSA, respectively. The binding average distance between the donor (HSA) and the acceptor was evaluated according to the Foster's theory of non-radiation energy transfer.This thesis is divided into four chapters:Chapter 1:The sources and hazards of endocrine disruptors were introduced briefly. The structures and natures of proteins and the methods used to study interaction of ligands with proteins were reviewed. Meanwhile, the developments of interaction between endocrine disruptors and HSA were summarized.Chapter 2:The interaction of bisphenol A and HSA has been characterized by molecular modeling and spectroscopic methods. The binding mode between bisphenol A and HSA were studied by molecular docking technique. The quenching of HSA fluorescence take place with a binding constant and the number of binding site at four different temperatures, respectively. The thermodynamic parameters were calculated according to the Van't Hoff equation. The alterations of protein secondary structure in the presence of bisphenol A were explored by FT-IR and CD spectra. The distance between the tryptophan residues in HSA and bisphenol A was evaluated using Foster's equation on the basis of fluorescence energy transfer.Chapter 3:The binding characteristics of HSA with three phthalate esters (PAEs) such as dimethyl phthalate (DMP), butylbenzyl Phthalate (BBP), and di-2-ethylhexyl phthalate (DEHP) were studied by employing spectroscopy and molecular modeling, respectively. Fluorescence titration data indicated that DMP could bind to one class of sites on HSA, while the scatchard plots for the HSA-BBP and HSA-DEHP showed that these bindings were via two types of binding sites. Thermodynamic analysis indicated that hydrophobic interaction dominated in the association reaction. Time-resolved fluorescence studies showed that the lifetime of Trp residue of HSA decreased after the addition of PAEs, which implied that the three PAEs bind to residues located in subdomain IIA of HSA. The effects of the three PAEs on the secondary structure of HSA were investigated by FT-IR and CD techniques.Chapter 4:The fluorogenic enhancement effect of two alkylphenols endocrine disruptors such as 4-tert-octylphenol and 4-nonylphenol were exploited for the first time to analyze the interactions with HSA as a probe. The affinity constants under different temperatures were obtained from the experimental results. The thermodynamic functions enthalpy and entropy for the reactions were calculated according to Vant's Hoff equation. The decreasings of lifetime of Trp residue showed that the polarity around Trp residue were decreased, the secondary structures of HSA were changed. The distances between the tryptophan residues in HSA and the two alkylphenols were evaluated according to the Forster's theory of non-radiation energy transfer.