Experimental and molecular docking study of the binding interactions between bovine α-lactalbumin and oleuropein

Oleuropein (OLE) is the major phenolic compound of olive leaves, known for its numerous health benefits. α-lactalbumin (ALA) is a milk protein constituting almost 20% of whey proteins with a high nutritional value owing to its essential amino acids. In this study, binding properties of OLE to ALA was explored by fourier transform infrared (FTIR) spectroscopy, fluorescent spectroscopy, dynamic light scattering, circular dichroism (CD) spectroscopy and molecular docking. The experimental results revealed a decrease in the fluorescence units due to binding process with fluorescent residues, especially with Trp104 which was then confirmed by CD spectroscopy and FTIR data and molecular docking. Also, the increase of OLE content resulted in the formation of a stable complex with a zeta potential near −15 mV. The size of the complex decreased after addition of more OLE to the protein which was attributed to the formation of hydrogen bonds and folding of protein structure. Moreover, molecular docking indicated that hydrogen bonding plays a crucial role in the formation of OLE-ALA complexes including amide groups of Asn44 and Asn56 with the hydroxy groups of OLE. These findings indicated that ALA may be an ideal nanocarrier to load OLE for further applications in food and pharmaceutical fields.