Binding mechanism of methyl-α-N-acetyl-D-galactopyranosyl amine to <i>Artocarpus lakoocha </i>lectin, artocarpin: A proton nuclear magnetic resonance study

299-306The dynamics of the binding mechanism between Artocarpus lakoocha lectin and Me-α-D-GalNAc has been studied using 1H NMR spectroscopy. Various thermodynamic parameters have been calculated with the help of temperature dependence of line broadening of the methoxy group resonance of Me-α-D-GalNAc. No change in the chemical shift has been observed while full line width at half height of the sugar protons was found to increase with increasing temperature indicating that the binding ligand is in fast exchange. No chemical shift between bound and free ligands has been observed.The activation parameters obtained from the association and dissociation rate constants suggest that the association process is controlled by high activation entropy which is due to the specific orientation of both lectin and sugar whereas the contribution of activation enthalpy is small. On the other hand, the dissociation reaction is controlled by high activation enthalpy due to the break in the interaction between the sugar and the lectin. From NMR data a two-step binding mechanism has been proposed. The associated complex is stabilized mainly by hydrogen bonding and vander Waals attractions while hydrophobic interaction is not significant as indicated by the negative entropy and enthalpy values