Unraveling the molecular interaction of hydroxytyrosol with human serum albumin via multi-spectroscopy, thermodynamic...

Hydroxytyrosol (HT) is a powerful antioxidant that scavenges free radicals and protects cells and also is one of the main active ingredients in functional foods. Recently, the consumption of HT has been increasing due to its excellent biological and pharmacological effects. However, the interaction of HT and major proteins in the circulatory system remains unclear. Herein, Human Serum Albumin (HSA) binding interactions with HT were analyzed on a molecular level through multi-spectroscopy analysis, thermodynamic analysis, molecular docking and molecular dynamics (MD) simulation in the present study. UV-vis absorption spectroscopy, three-dimensional (3D) fluorescence spectroscopy, synchronous fluorescence spectroscopy, circular dichroism (CD) spectroscopy, FT-IR spectroscopy and surface hydrophobicity experiment revealed that HT induced conformational changes and a slight secondary structure changes in HSA. Thermodynamic analysis and site competition experiments demonstrated that HT was bound predominantly to HSA's Sudlow site I via hydrophobic forces (ΔH > 0, ΔS > 0) and was a spontaneous process (ΔG < 0). The HSA quenching fluorescence mechanism by HT is dominated with a static quenching mechanism accompanied by a weak dynamic quenching mechanism. The molecular docking results showed that HT was more stable bound to HSA's Sudlow site I (-25.12 kJ·mol^-1) than Sudlow site III and Sudlow site II. Moreover, HT binds to HSA via hydrophobic and hydrogen bond interactions, as also validated by molecular docking and MD simulations. In summary, this study contributes to an advanced understanding of HSA-HT interactions as well as to a theoretical understanding of the interplay between HT absorption, distribution, and transport.