Thermodynamics of lectin-sugar interaction: binding of sugars to winged bean (Psophocarpus tetragonolobus) basic aggIutinin (WBAI)

Abstract

Combining site of WBAI is extended and encompasses all the residues of blood group A-reactive trisaccharide [GalNAcα3Galβ4Glc]. Though both of the fucose residues of A-pentasaccharide [GalNAcα(Fucα2)3Galβ(Fucα3)4Glc] do not directly interact with the combining site they thermodynamically favour the interaction of GalNAcα3Galβ4Glc part of the molecule by imposing a sterically favourable orientation of the binding epitope viz. GalNAcα3Galβ4Glc of the saccharide. Binding of sugars is driven by enthalpy and is devoid of heat capacity changes. This together with enthalpy-entropy compensation observed for these processes underscore the importance of water reorganization as being one of the principal determinant of protein-sugar interactions.