Influence of protein conformation and selected Hofmeister salts on bovine serum albumin/lutein complex formation

Protein conformation and the 3D water structure play important roles in the ability of bovine serum albumin (BSA) to form stable nanostructures with bioactive molecules. We studied the influence of BSA unfolding and those of two Hofmeister salts, sodium chloride (NaCl) as kosmotrope and sodium thiocyanate (NaSCN) as chaotrope, on BSA/lutein binding at pH 7.4 using fluorescence spectroscopy. The BSA/lutein complex formation was entropically driven and lutein was preferentially bound to site III of BSA. The binding constant (104 L mol−1), complex stoichiometry (1:1), and thermodynamic potential for BSA/lutein binding were independent of protein conformation and Hofmeister salts. However, the enthalpic and entropic components of BSA/lutein binding in the presence of NaSCN decreased as the temperature increased. The opposite was observed for BSA/lutein binding in the presence of NaCl and for denatured BSA/lutein binding. Therefore, the BSA conformation and 3D water structure directly affected the BSA/lutein binding thermodynamics. •Bovine serum albumin (BSA) and lutein (LUT) formed a stable complex.•LUT bound to site III of BSA by an entropically driven process.•The hydrophobic effect drove the denatured-BSA/LUT complex formation.•Entropy-enthalpy compensation occurred for BSA/LUT binding in the presence of NaSCN.•The BSA/LUT binding in the presence of NaCl was driven by the increase in entropy.