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

Abstract

The molecular interaction between bovine lactoferrin (LF) and (−)-epigallocatechin-3-gallate (EGCG) was investigated in an aqueous solution at pH6.0. 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.