The interaction between β-Lactoglobulin and allyl-isothiocyanate

Abstract

Beta-Lactoglobulin (β-Lg) is a globular milk protein and a major component of whey (~50% dry weight). β-Lg binds strongly to various hydrophobic ligands and may act as a transporter for these molecules. Monomeric β-Lg has two disulfide bonds and one free thiol group that have important roles in the formation of the tertiary structures of β-Lg. As a result, β-Lg reacts to pH changes in a very specific manner. In this study, isothermal titration calorimetry (ITC) and circular dichroism (CD) were used to investigate the interaction between β-Lg and allyl isothiocyanate (AITC) at different pH values 3.0, 6.5 and 8.5. The interaction was characterized using total reflectance Fourier-transform infrared spectroscopy and molecular docking. The final thermograms from ITC were fitted to three sites of a sequential binding model (Koshland model), showing the high affinity between β-Lg and AITC with binding constants of 104–105 M−1. ITC and CD results showed that AITC binding at different pH changes the secondary structure of β-Lg. FTIR results showed the binding of AITC with strong isothiocyanate peaks between 1900 and 2150 cm−1. Three different AITC-binding sites to β-Lg were confirmed using molecular docking. The results showed that the characteristic properties of the interaction between β-Lg and AITC can be used to predict the nanotransporter capacity of β-Lg for bioactive materials at different pH values.