Elucidation of energetics and mode of recognition of green tea polyphenols by human serum albumin

Green tea is rich in several polyphenols which has many beneficial biological effects. We have done a detailed qualitative and quantitative study on binding of two polyphenol (-)-epicatechin (EC) and (-)-epigallocatechin-3-gallate (EGCG) with human serum albumin (HSA) by using a combination of isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), steady-state fluorescence, and circular dichroism spectroscopies. The binding constants obtained from isothermal titration calorimetry for EC-HSA and EGCG-HSA complexes are (2.09 +/- 0.08) x 10(4) and (1.84 +/- 0.30) x 10(5), respectively. The effects of ionic strength and additives of polar and non-polar characters indicate contribution of a mix of ionic, hydrogen bonding and hydrophobic interactions in the polyphenol-HSA association process. The 3D fluorescence analysis and circular dichroism (CD) studies reveal that the complexation of EGCG induces significant conformational change in HSA. The DSC results also show that the binding of EGCG is stronger compared to that of EC and provides quantitative information on the effect of these polyphenols on the thermal stability of HSA. Such studies play a crucial role in understanding the mechanism of drug-protein interactions and optimization of various binding parameters for successful drug delivery. (C) 2018 Elsevier B.V. All rights reserved.