Analysis of binding interaction of genistein and kaempferol with bovine α-lactalbumin

• Kaempferol and genistein come closer to the Trp-60 than to other tryptophans of BLA.
• Kaempferol and genistein bind to BLA by three and five hydrogen bonds, respectively.
• The main mechanism of fluorescence quenching of BLA by kaempferol and genistein is static.

The fluorescence quenching measurements and docking studies were used for investigating the binding of kaempferol and genistein as functional food ingredients to bovine α-lactalbumin (BLA) as a natural vehicle for bioactive ions and molecules. The closeness of the tryptophan residues to the bound ligands than to the tyrosine residues and the considerable change in microregion of the tryptophan residues in BLA is observed upon the binding of the genistein and kaempferol to BLA by synchronous fluorescence. The essential parameters which describe the characteristics of the binding such as the thermodynamic parameters, the binding constants and the binding stoichiometry were obtained from the fluorescence quenching measurements. The extent of vicinity of the bound ligands to the tryptophan residues of BLA was estimated by Förster's distance. The major role of hydrogen bonds in stabilizing the final ligand–protein complexes was concluded from the thermodynamic parameters which were calculated in different temperatures. The results of docking studies indicated that kaempferol and gnistein come closer to the Trp-60 than to other tryptophans and bind to BLA by three and five hydrogen bonds, respectively. The calculated distances between bound ligands and tryptophans obtained by docking studies were in agreement with fluorescence resonance energy transfer results. These findings can reveal that BLA can not only carry the metal ions, but also has binding affinity for natural polyphenolic compounds.