Towards understanding the interaction of β-lactoglobulin with capsaicin: Multi-spectroscopic, thermodynamic, molecular docking and molecular dynamics simulation approaches

This study systematically investigated the binding mechanism between capsaicin (CAP) and beta-lactoglobulin (beta-lg) through the method of multi-spectroscopic, thermodynamics, molecular docking, and molecular dynamics simulation at pH 7.4. The results showed that CAP could interact with beta-lg to enhance the fluorescence intensity of beta-lg. Simultaneously, the complex formed by CAP and beta-lg enhanced the hydrophobicity of the microenvironment of Trp and Tyr in beta-lg. The change in particle size without changing the secondary structure of beta-lg indicates a transition between the large aggregate particle to small aggregate particle of beta-lg. Isothermal titration calorimetric (ITC) results show that hydrophobic interactions play an important role in the formation of the complex. The MD simulation results showed that the RMSD of the systems reached equilibrium and wiggle around the mean value after 30 ns of simulation time. Analysis of Rg indicated that beta-lg and beta-lg/CAP complex was stabilized around 30 ns. Secondary structure analysis results showed that CAP has no distinct effect on the beta-lg structure. Furthermore, the van der Waals interactions are also involved in binding between beta-lg and CAP according to the result of MD simulation. The calculational results indicated that CAP preferred to bind to the hydrophobic pocket of beta-lg. The obtained results could provide some new clues to the interaction mechanism of beta-lg and CAP, which proved that beta-lg possesses the ability to apply in functional food as the vehicle of capsaicin.