A predominantly hydrophobic recognition of H‐antigenic sugars by winged bean acidic lectin: a thermodynamic study

Abstract

The thermodynamics of binding of winged bean (Psophocarpus tetragonolobus) acidic agglutinin to the Hantigenic oligosaccharide (FucK K1-2GalL L1-4GlcNAc-oMe) and its deoxy and methoxy congeners were determined by isothermal titration calorimetry. We report a relatively hydrophobically driven binding of winged bean acidic agglutinin to the congeners of the above sugar. This conclusion is arrived, from the binding parameters of the fucosyl congeners, the nature of the enthalpyentropy compensation plots and the temperature dependence of binding enthalpies of some of the congeners. Thus, the binding site of winged bean acidic agglutinin must be quite extended to accommodate the trisaccharide, with non-polar loci that recognize the fucosyl moiety of the H-antigenic determinant.z 1999 Federation of European Biochemical Societies.

Carbohydrate specificity and salt-bridge mediated conformational change in acidic winged bean agglutinin 1 1Edited by A. Klug

“…The binding is still higher when the methyl group is present, as required by the model involving conformation I. Also the 85-fold stronger af®nity of 2-fucosyllactose compared to that of 2fucosylgalactose (Srinivas et al, 1999) implies an extended binding site in WBAII The hydrogen bonds with Gln216 and the van der Waals and hydrophobic interactions with Tyr215 involving GlcNAc in the model is in qualitative conformity with this conclusion.…”

“…Thermodynamic measurements (Srinivas et al, 1999) show much reduced af®nity of 3O-Gal, 4O-Gal and 6O-Gal deoxy analogues of the H-type II oligosaccharide to WBAII, con®rming the role of the primary hydrogen-bonding interactions. The 2-deoxy fucosyl congener binds with a tenfold reduced binding af®nity while binding is altogether abolished in the corresponding 2-methoxy congener.…”

“…An attempt is made here to relate the available thermodynamic data on WBAII (Srinivas et al, 1998(Srinivas et al, , 1999 with its structure in a qualitative manner, as has been done for conA, (Bradbrook et al, 1998;Moothoo & Naismith, 1998;Moothoo et al, 1999) and EcorL (Moreno et al, 1997), with emphasis on comparative af®nities rather than on absolute values. For this purpose, the models of Htype II trisaccharide (Fuca2Galb4GlcNAcb) belonging to the two conformational families (hereafter referred to as conformations I and II) suggested by Imberty et al (1995) were separately docked into the sugar binding site of WBAII and EcorL, and the complexes were re®ned using energy minimisation.…”

“…Lectin-carbohydrate interactions are generally enthalpically driven and exhibit enthalpy-entropy compensation (Toone, 1994;Chervenak & Toone, 1995). Srinivas et al (1999), have commented on the relative predominance of the entropic factor in the energetics of binding of WBAII to fucosylated saccharides and also noted a distinct change in heat capacity upon binding, not yet observed in any other lectin-sugar interaction. The model of the complex provides a qualitative rationale for this unique property of the lectin.…”

The primary structure of the acidic lectin from winged bean (Psophocarpus tetragonolobus): insights in carbohydrate recognition, adenine binding and quaternary association

“…Quite unusually, the binding of these fucosylated sugars is more entropically driven than their non‐fucosylated counterparts (viz. galactose and lactose) suggesting an extended binding site with perhaps a hydrophobic region that recognizes the fucosyl moiety [7,8]. In addition, the thermal unfolding of WBA II suggests that its denaturation occurs independent of its subunit dissociation.…”