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.

Thermodynamic and kinetic analyses of curcumin and bovine serum albumin binding.

Bovine serum albumin (BSA)/curcumin binding and dye photodegradation stability were evaluated. BSA/curcumin complex showed 1:1 stoichiometry, but the thermodynamic binding parameters depended on the technique used and BSA conformation. The binding constant was of the order of 105L·mol-1 by fluorescence and microcalorimetric, and 103 and 104L·mol-1 by surface plasmon resonance (steady-state equilibrium and kinetic experiments, respectively). For native BSA/curcumin, fluorescence indicated an enthalpic and entropic driven process based on the standard enthalpy change (ΔH○F=-8.67kJ·mol-1), while microcalorimetry showed an entropic driven binding process (ΔH○cal=29.11kJ·mol-1). For the unfolded BSA/curcumin complex, it was found thatp ΔH○F=-16.12kJ·mol-1 and ΔH○cal=-42.63kJ·mol-1. BSA (mainly native) increased the curcumin photodegradation stability. This work proved the importance of using different techniques to characterize the protein-ligand binding.