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Chemicobiological Deciphering the Protein-Binding Details of Aspirin

Hang-Xing Xiong, Hong-Lin Wang, Hua-Xin Zhang and Li-Wei Li

Fluorescence quenching and fluorescence resonance energy transfer (FRET) theories are widely used in drug-protein binding study, but the inner filter effect is not always being corrected, which may cause inaccurate results. In view of this, the interaction of aspirin (ASP) with human serum albumin (HSA) was studied by three-dimensional fluorescence spectra, ultraviolet spectra, circular dichroism (CD) spectra, and molecular modeling methods. The inner effect was subtracted from raw data of the fluorescence when evaluating the number of binding sites, equilibrium constants, and thermodynamic parameters. The results showed that only one binding site formed on HSA and it obviously impaired by increasing temperature. The negative Gibbs free energy change (Gθ) suggested the binding was spontaneous. Meanwhile, negative enthalpy change (Hθ) and entropy change (Sθ) indicated hydrogen bonds had an important influence in the formation of ASP-HSA complex. The distance between donor and acceptor was calculated according to Förster’s non-radiation resonance energy transfer theory using the corrected fluorescence data. Synchronous spectra implied the polarity of tryptophan residue increased, which gave a clue to binding location. CD spectra were employed to detect the secondary structural changes of HSA. Based on experimental results, molecular modeling was carried out to calculate the most optimized docking mode, in which both panorama and details were involved.