Spectroscopic and docking studies of the interaction mechanisms of xylitol with α-casein and κ-casein

The molecular interactions of xylitol (XY) with α-casein (α-CN) and κ-casein (κ-CN) at pH 7.4 as a function of temperature (298, 308, and 318 K) were characterized by multispectral techniques and molecular docking. The fluorescence results showed that XY strongly quenched the intrinsic fluorescence of α- and κ-CN by static quenching, as well as the presence of a single binding site for XY on both proteins with a binding constant value of ∼10⁵ L/mol. The binding affinity of both proteins for XY decreased with increasing temperature, and Van der Waals forces, hydrogen bonding and protonation were the key forces in the interactions. The addition of XY altered the polarity of the microenvironment of proteins and changed their secondary structure from ordered to disordered. The molecular docking results showed that XY had different binding sites to α- and κ-CN, with several amino acids involved in the binding processes.