A comparison study of the interaction between β-lactoglobulin and retinol at two different conditions: spectroscopic and molecular modeling approaches

The interaction between bovin beta-Lactoglobulin (beta-LG) and retinol at two different pH values was investigated by multispectroscopic, zeta potential, molecular modeling, and conductometry measurements. The steady state and polarization fluorescence spectroscopy revealed that complex formation at two different pH values could occur through a remarkable static quenching. According to fluorescence quenching, one set of binding site at pH 2 and two sets of binding sites at pH 7 were introduced for binding of retinol to beta-LG that show the enhancement of saturation score of beta-LG to retinol in dimmer condition. The polarization fluorescence analysis represented that there is more affinity between beta-LG and retinol at pH 7 rather than at pH 2. The effect of retinol on beta-LG was studied by UV-visible, circular dichroism (CD), and synchronous fluorescence, which indicated that retinol induced more structural changes on beta-LG at pH 7. beta-LG-retinol complex formation at two different pH values was recorded via applying resonance light scattering (RLS) and zeta potential. Conductometry and RLS showed two different behaviors of interaction between beta-LG and retinol at two different pH values; therefore, dimmer formation played important roles in different behaviors of interaction between beta-LG and retinol. The zeta potential was the implied combination of electrostatic and hydrophobic forces which are involved in beta-LG-retinol complex at two different pH values, and the hydrophobic interactions play a dominant role in complex formation. Molecular modeling was approved by all experimental results. The acquired results suggested that monomer and dimmer states of beta-LG can be induced by retinol with different behaviors.