Conjugation of One Polyol (xylitol) with Trypsin: Spectroscopic and Theoretical insights

The aim of the present study was to investigate how xylitol could influence the structure and thermal stability of trypsin. The influence of xylitol on the structure and stability of trypsin explored using thermal stability, fluorescence spectroscopy, circular dichroism (CD) studies and molecular docking. We have calculated the thermodynamic parameters of transition temperature (Tm), enthalpy change (∆H°), entropy change (∆S°) and Gibbs free energy change (∆G°) to understand trypsin stability. Xylitol acted as enhancers for trypsin stability, with varying efficiencies and efficacies. The result reveals the ability of xylitol to protect the native structural conformation of trypsin. These results explicitly illustrate that stabilizing xylitol is preferentially excluded from the surface of trypsin, since water has a higher tendency toward favorable interactions with functional groups of trypsin than with xylitol. Fluorescence intensity changes showed static quenching during the xylitol binding. The trypsin fluorescence quenching suggested the more polar location of Trp residues. Near-UV and Far- UV CD studies also are proven the transfer of Trp, Phe and Tyr residues to a more flexible environment. Increasing of the trypsin absorption in the presence of xylitol was as a result of the formation of a xylitol – trypsin complex. Molecular docking results revealed a negative value for the Gibbs free energy of the binding of xylitol to trypsin and the presence of one binding site. Docking study also revealed that hydrogen bonds interactions dominated in the binding site. Moreover, the increased thermal stability of trypsin might be due to the lower surface hydrophobicity and the higher hydrogen bond formation after xylitol enhancing, which was reflected in the increase of UV absorbance, the quenching, as well as the increase of α-Helix content.