Comparison of carrying mechanism between three fat-soluble vitamins and alpha-lactalbumin: Effects on structure and physicochemical properties of alpha-lactalbumin

Abstract This study aims to explore the interaction mechanisms between alpha-lactalbumin (ALa) and three fat-soluble vitamins (VA, VD3 and VE) at pH 7.0 and their impacts on structure and functionality of ALa. Analysis of fluorescence spectroscopy showed that vitamins quenched intrinsic fluorescence of ALa in a static mode and cholecalciferol (VD3) had a higher binding affinity for ALa than Retinol (VA) and alpha-tocopherol (VE). Synchronous fluorescence and three-dimensional fluorescence spectra demonstrated the conformation changes of ALa. Meanwhile, fourier transform infrared spectroscopy manifested that three vitamins induced a transition from α-helix to β-sheet in ALa, and VD3 notably increased its random coil content. Furthermore, a combination of VE with ALa generated macromolecular aggregates, based on particle size results. The addition of VA and VD3 increased zeta potential and surface hydrophobicity of ALa, while VE triggered that of ALa initially increased and then decreased with vitamins ranging from 0 to 0.35 mmol/L. Additionally, molecular simulation suggested that VA and VE had a same binding site in the cleft of ALa, but VD3 bound in a hydrophobic pocket in protein, and their binding driving forces were hydrophobic interaction and hydrogen bond. This study reveals that ALa might be a potentially suitable carrier for delivering vitamins, providing a theoretical basis of interaction between proteins and small molecules.