Raman Spectroscopic Studies On The Interactions Between Human Serum Albumin And Drugs

HSA (Human serum albumin), the most abundant protein of plasma, is a heart-shaped, monomeric protein of 585 amino acids. HSA is composed of three homologous domains (labeled I -III) and each with two subdomains (A and B). Altogether, roughly 67% of HSA is helical, with a remainder in turns and extended polypeptide and a large number of disulphide bridges. HSA can help to maintain colloidal osmotic blood pressure and detoxify by binding poisonous metabolites. Additionally, HSA can carry a wide variety of both endogenous and exogenous substances. HSA is one of the main protein involved in the binding of drugs, with two major primary binding sites located in subdomain IIA and subdomain III A. The binding of ligands to proteins occurs mostly through weak non-covalent interactions, namely hydrophobic interaction, van der Waals forces, and hydrogen bonding. Raman spectroscopy is a powerful method to study the structure of protein and its transformations, especially in solution and in living system. In this thesis, Raman spectroscopy was used to study transformation of conformations and decide the binding site. The main results are as follows:(1) The binding of three drugs to HSA induces the transformation of Raman spectra of the unique tryptophan residues. Since the drugs employed in this thesis are hydrophobic molecules, they can better penetrate into the hydrophobic subdomain II A, where Trp214 is located.(2) The binding of three drugs to HSA changes the conformation of the disulfide bonds. Since the binding site I is located in the part of the cavity created by a smaller disulfide double loop within the region of inter-domain connections, it seems to be logically suggested that the two disulfide bridges within the smaller disulfide double loop change their conformation upon binding of the three drugs.(3) The binding of three drugs to HSA induces the transformation of Raman spectra of tryptophan residue. The transformations of tryptophan residue andtryptophan residues suggest the existing of hydrophobic interaction.