BACKGROUND: Curcumin has emerged to be utilized as a superb beneficial agent, due to its naturally occurring anti-oxidant, anti-inflammatory and anti-carcinogenic property.

METHODS: The interaction of curcumin with human serum albumin, the main in vivo transporter of exogenous substances, was investigated using absorption spectroscopy, steady-state fluorescence, excited state life-time studies and circular dichroism spectroscopy.

RESULTS: Isothermal titration calorimetry techniques inferred one class of binding site with binding constant ～1.74×10⁵ M⁻¹ revealing a strong interaction. The binding profile was analyzed through the evaluation of the thermodynamic parameters, which indicated the involvement of hydrophobic interactions (burial of non-polar group). Fluorescence lifetime of tryptophan residue was observed to decrease to 1.94 ns from 2.84 ns in presence of Curcumin. Percentage of α helicity of human serum albumin was also reduced significantly upon binding with curcumin as evidenced by circular dichroism measurement leading to conformational modification of the protein molecule.

CONCLUSIONS: On the basis of such complementary results, it may be concluded that curcumin shows strong binding affinity for human serum albumin, probably at the hydrophobic cavities of the protein and at or around the tryptophan residue. Molecular Docking analysis of HSA and curcumin provided light on the number of binding sites at an atomic level, which were already determined at a molecular level in spectroscopic measurements. Our study unfolds the modes of interaction of curcumin with human serum albumin in the light of different biophysical techniques and molecular modeling analysis.