Interaction between an (−)-epigallocatechin-3-gallate-copper complex and bovine serum albumin: Fluorescence, circular dichroism, HPLC, and docking studies

The interaction of copper complexed with (-)-epigallocatechin-3-gallate (EGCG) and bovine serum albumin (BSA) was investigated using fluorescence, circular dichroism (CD) spectroscopy, HPLC and protein-ligand docking. The fluorescence quenching efficiency of BSA by EGCG was enhanced after EGCG was complexed with copper, and the EGCG-Cu complex exhibited a higher apparent binding affinity (8.88 × 105 M-1) to BSA compared with EGCG alone (5.17 × 105 M-1). The CD experiment showed that both the EGCG-BSA and [EGCG-Cu]-BSA interactions resulted in the unfolding of the secondary structure of the protein. Results of competitive binding experiments confirmed that the location of EGCG and EGCG-Cu complex binding in BSA was site I. Furthermore, molecular modeling was used to identify the amino acid residue in site I and site II that play key roles in this binding interaction. The data suggest that most of the residues involved in the [EGCG-Cu]-BSA reaction belong to the subdomains IIa (site I) of BSA.