Combined spectroscopic and molecular docking study on the pH dependence of molecular interactions between β-lactoglobulin and ferulic acid

Interactions between p-lactoglobulin and ferulic acid were investigated at ambient temperature in relation to the dimer and monomer forms of the protein at pH 7.3 and 2.4, respectively. To this end, molecular dynamics (MD) simulations and a variety of spectroscopic methods were employed. Circular dichmism (CD) and Fourier transform infrared (FTIR) analysis indicate that the secondary structure of the protein is altered upon complexation, suggesting molecular interactions do occur in both the monomer and dimer forms. However, UV-vis measurements of beta-lactoglobulin remain constant upon complexation with ferulic acid, indicating that interactions are non-covalent in nature and are likely stabilised by hydrophobic forces and hydrogen bonds. Fluorescence quenching confirms the presence of a binding state, with the monomeric complex producing a stronger dissociation constant than the dimeric counterpart. Docking studies and MD simulations indicate that the preferred binding site in the dimer form (pH 7.3) lies at the interface of the two monomers. In contrast, the preferred binding site for the monomer form (pH 2.4) lies within the calyx shaped beta-barrel structure and is stabilised by hydrogen bonds and pi - alkyl interactions.