Molecular interaction between (−)-epigallocatechin-3-gallate and bovine lactoferrin using multi-spectroscopic method and isothermal titration calorimetry

The molecular interaction between bovine lactoferrin (LF) and (−)-epigallocatechin-3-gallate (EGCG) was investigated in an aqueous solution at pH 6.0. The presence of EGCG did not change the size and turbidity of LF-EGCG complex in an aqueous solution until the LF/EGCG molar ratio was over a critical value of 1:25. The fluorescence spectra revealed that both tryptophanyl and tyrosyl groups of LF were associated with the interaction with EGCG. The infrared spectra of freeze-dried LF-EGCG complexes showed that they were different from those of LF and EGCG alone, FTIR and far-UV CD results indicated that EGCG induced a progressive increase in the proportion of α-helix structure at the cost of β-sheet structure of LF. The near-UV CD data testified that LF tertiary conformation was altered in the presence of EGCG. Isothermal titration calorimetry (ITC) analysis implied that EGCG was spontaneously bound to LF by a two-stage mechanism, about 31 EGCG molecules were integrated with 1 molecule LF and hydrogen bonds were always involved in the assembly process.