Energetics and mechanism of β-lactoglobulin binding to dextran sulfate

Abstract Interactions of a major whey protein, β-lactoglobulin (BLG), with an anionic polysaccharide, dextran sulfate (DS), were investigated by nephelometric titration and high-sensitivity differential scanning calorimetry at pH 2.5–7.0 and NaCl concentrations of 0–500 mM. The pH-dependences of the light scattering of the BLG−DS system revealed a maximum. Its position was dependent on the polysaccharide/protein ratio and salt concentration. Thermodynamic parameters of the denaturation of BLG in mixtures with DS were determined at different pH and salt concentrations. Conformational stability of BLG in the BLG–DS complexes was shown to either increase or decrease depending on the solution conditions and complex composition. The binding curves of BLG to DS were calculated from the light scattering and calorimetric data and analyzed using various binding models including the Langmuir and McGhee–von Hippel models as well as a stoichiometric interpolyelectrolyte reaction. Mechanisms responsible for changes in the BLG oligomer structure and conformational stability induced by the complex formation with the polysaccharide were proposed.