THERMODYNAMICS OF LECTIN SUGAR INTERACTION - BINDING OF SUGARS TO WINGED BEAN (PSOPHOCARPUS-TETRAGONOLOBUS) BASIC AGGLUTININ (WBAI)

Combining site of WBAI is extended and encompasses all the residues of blood group A-reactive trisaccharide [GalNAcalpha3Galbeta4Glc]. Thoug h both of the fucose residues of A-pentasaccharide [GalNAcalpha(Fucalp ha2)3Galbeta(Fucalpha3)4Glc] do not directly interact, with the combin ing site they thermodynamically favour the interaction of GalNAcalpha3 Galbeta4Glc part of the molecule by imposing a sterically favourable o rientation of the binding epitope viz. GalNAcalpha3Galbeta4Glc of the saccharide. Binding of sugars is driven by enthalpy and is devoid of h eat capacity changes. This together with enthalpy-entropy compensation observed for these processes underscore the importance of water reorg anization as being one of the principal determinant of protein-sugar i nteractions.