Binding interaction of harpagoside and bovine serum albumin: spectroscopic methodologies and molecular docking / 中国中药杂志

Scrophularia ningpoensis has exhibited a variety of biological activities and been used as a pharmaceutical product for the treatment of inflammatory ailment, rheumatoid arthritis, osteoarthritis and so on. Harpagoside (HAR) is considerer as a main bioactive compound in this plant. Serum albumin has important physiological roles in transportation, distribution and metabolism of many endogenous and exogenous substances in body. It is of great significance to study the interaction mechanism between HAR and bovine serum albumin (BSA). The mechanism of interaction between HAR and BSA was investigated using 2D and 3D fluorescence, synchronous florescence, ultraviolet spectroscopy and molecular docking. According to the analysis of fluorescence spectra, HAR could strongly quench the fluorescence of BSA, and the static quenching process indicated that the decrease in the quenching constant was observed with the increase in temperature. The magnitude of binding constants (KA) was more than 1×10⁵ L·mol⁻¹, and the number of binding sites(n) was approximate to 1. The thermodynamic parameters were calculated through analysis of fluorescence data with Stern-Volmer and Van't Hoff equation. The calculated enthalpy change (ΔH) and entropy change (ΔS) implied that the main interaction forces of HAR with BSA were the bonding interaction between van der Waals forces and hydrogen. The negative values of energy (ΔG) demonstrated that the binding of HAR with BSA was a spontaneous and exothermic process. The binding distance(r) between HAR and BSA was calculated to be about 2.80 nm based on the theory of Frster's non-radiation energy transfer, which indicated that energy is likely to be transfer from BSA to HAR. Both synchronous and 3D florescence spectroscopy clearly revealed that the microenvironment and conformation of BSA changed during the binding interaction between HAR and BSA. The molecular docking analysis revealed HAR is more inclined to BSA and human serum albumin (HSA) in subdomain ⅡA (Sudlow's site I). This study will provide valuable information for understanding the action mechanism of HAR.

Spectroscopic Study of Interaction of Harpagoside and Human Serum Albumin / 分析化学

Harpagoside (HAR) is believed to be a main compound in Scrophularia ningpoensis which possess a broad of biological activities.Human serum albumin (HSA) has important physiological roles in transportation, distribution and metabolism of many endogenous and exogenous substances in body.It is great significance in pharmacology to investigate the interaction mechanism of HAR and HSA.In this work, the interaction between HAR and HSA was investigated by fluorescence and ultraviolet absorption spectroscopy at different pH (pH=4.0, 7.4, and 9.0) and temperatures (297, 310 and 323 K).The experimental results showed that the HAR could cause the fluorescence quenching of HSA through a static quenching procedure, showing that the HAR regularly quenched the intrinsic fluorescence of HSA, and a decrease in the quenching constant was observed with an increase in temperature.Under different conditions, all the magnitude of binding constants (KA) was larger than 105 L/mol and the number of binding sites (n) in the binary system were approximate to 1.Base on the magnitude of enthalpy and entropy changes, the negative values of ΔG, ΔH and ΔS revealed that the binding of HAR with HSA was spontaneous and exothermic process, and the main interaction forces of the HAR with HAR were van der Waals forces and/or hydrogen bonding interaction.The binding distance (r) between the HAR and HSA was calculated to be about 4.2 nm based on the theory of F(o)rster′s nonradiation energy transfer, which indicated that the energy transfer from HSA to HAR occurred with high possibility.What was more, the synchronous florescence spectroscopy confirmed the conformational changes of HSA during the binding reaction.