Study On The Interaction Between Small Dye/Drug Molecules And Protein

Serum albumin being the major ligand binding and transport protein of circulatory system is considered as a model protein for studying small molecules-protein interaction in vitro. Human serum albumin (HSA), the main protein in the blood plasma acting as the transporter and disposition of endogenous and exogenous compounds, has been frequently used as a model protein for investigating the protein folding and ligand-binding mechanism. In most cases, small molecules interactions at protein binding level will significantly affect the apparent distribution volume of the small molecules. Considering the application of small molecules-protein interactions in diagnostic and pharmaceutical, the binding characteristics of human serum albumin with dyes, herbicide and drugs were studied by employing fluorescence, ultraviolet-visible (UV-vis), Fourier transform infrared (FT-IR), and circular dichroism (CD). The binding average distance between the donor (HSA) and the acceptor was evaluated according to the Foster's theory of non-radiation energy transfer; the effects of coexistent substances on the binding constants of small molecules-HS A complex were also discussed.This thesis is divided into five chapters:Chapter 1:Many small molecules which can interact with protein were presented. The types, structures, functions of proteins were introduced. The methods for the study of the interaction between small molecules and proteins were reviewed.Chapter 2:The interaction mechanism of herbicide glyphosate and human serum albumin has been characterized by fluorescence, UV, FT-IR, CD spectroscopic and molecular modeling methods. The structural characteristics of HSA and glyphosate were studied, and affinity constants were determined under different temperatures. The enthalpy changes and the entropy changes were calculated according to the Van't Hoff equation. These results indicated that glyphosate binds to HSA mainly by hydrogen bond and hydrophobic interaction can also not be excluded. The average binding distance, r, between the donor (HSA) and the acceptor (glyphosate) was evaluated according to the Forster's theory of non-radiation energy transfer. The alteration of protein secondary structure in the presence of glyphosate was confirmed by the evidences of UV, FT-IR and CD spectroscopies.Chapter 3:The binding characteristics of human serum albumin with C.I. Direct Yellow 9, C.I. Acid Green 1 were studied by employing spectroscopy and molecular modeling, respectively. Coexisting substances on the binding constant of C.I. Direct Yellow 9/C.I. Acid Green 1-human serum albumin complexes were investigated. Spectroscopic analysis showed that quenching of human serum albumin by the two dyes operates by a static quenching mechanism and the secondary structures of HSA were changed. The binding mode was investigated in terms of the association constants, number of binding sites and basic thermodynamic parameters.Chapter 4:The interactions between nobiletin, esculetin, mangiferin and human serum albumin were investigated by spectroscopy and molecular modeling. The results proved the formation of complex between the three active components of Chinese herbs drugs and HSA. Hydrophobic interaction dominated in the association reaction. The binding of the three active components to HSA leaded to changes in the conformation of HSA according to synchronous fluorescence spectra, FT-IR, UV-vis and CD data. The presence of coexisting substances affected the binding constant of esculetin/mangiferin-HSA complex. Computational mapping of the possible binding sites of the three drugs were also investigated.Chapter 5:This study was designed to examine the interaction of oxaliplatin with human serum albumin under physiological conditions by using fluorescence, UV-vis, FT-IR and CD spectroscopic techniques in combination with molecular docking. The quenching mechanism of oxaliplatin with HSA was static quenching. From the CD and FT-IR results, it was apparent that the interaction of oxaliplatin with HSA caused a conformational change of the protein. The result of molecular docking showed that oxaliplatin bind to residues located in subdomain IIA of HSA. The binding constant of HSA-oxaliplatin complex was affected by metal ions and amino acids.