Thermodynamics of ligand (substrate/end product) binding to endoxylanase from Chainia sp. (NCL-82-5-1): isothermal calorimetry and fluorescence titration studies.

The binding of xylo-oligosaccharides to Chainia endoxylanase resulted in a decrease in fluorescence intensity of the enzyme with the formation of 1:1 complex. Equilibrium and thermodynamic parameters of ligand binding were determined by fluorescence titrations and titration calorimetry. The affinity of xylanase for the oligosaccharides increases in the order X2<X3<X4</=X5. Contributions from the enthalpy towards the free energy change decreased with increasing chain length from X2 to X4, whereas an increase in entropy was observed, the change in enthalpy and entropy of binding being compensatory. The entropically driven binding process suggested that hydrophobic interactions as well as hydrogen bonds play a predominant role in ligand binding.