Calorimetric Analysis of the Binding of Lectins with Overlapping Carbohydrate-Binding Ligand Specificities

Abstract

The thermodynamics of binding of a system of plant lectins specific for the oligosaccharide methyl 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside have been studied calorimetrically. This system of lectins consists of concanavalin A, the lectin isolated from Dioclea grandiflora, and the lectin from Galanthus nivalis. The group thus contains lectins with similar structures and similar binding properties as well as lectins with different structures but similar binding properties. Concanavalin A and the lectin from Dioclea are highly homologous, while the lectin from Galanthus nivalis shares no sequence homology with either of the legume lectins, although it also binds the mannose trisaccharide tightly. Calorimetric data for oligosaccharide binding to both of the legume lectins suggests that the total binding site comprises a single high-affinity site and an additional extended site. The pattern of binding for the lectin from Galanthus is significantly different. Binding studies with the same saccharides indicate that the lectin has binding sites designed specifically for the 1-->3 and 1-->6 arms of the mannose trisaccharide that are unable to accommodate other saccharides. Enthalpy--entropy compensation was observed for several saccharides as a function of lectin structure. Contributions of solvation effects to the enthalpy of binding and the configurational entropies were determined experimentally. For those systems studied here, solute-solute attractive interactions and configurational entropies were the greatest contributors to enthalpy-entropy compensation. Our studies clearly demonstrate that, despite their common affinity for the mannose trisaccharide, the three lectins bind oligosaccharides very differently.

A Comparison of the Fine Saccharide‐Binding Specificity of Dioclea grandiflora Lectin and Concanavalin A

“…The same is true for a(1-6) dimannosides 9 and 10, which are similar. These observations confirm recent titration microcalorimetry results for the binding of DGL and ConA to 5 and 10, respectively (Chervenak and Toone, 1995). Oligosaccharide 7 which possesses a 4dMan residue at the reducing terminal of a(1-3) dimannoside 5 shows nearly 13-fold enhanced affinity for ConA, relative to the binding of a-ManMe, but only a threefold enhanced affinity for DGL.…”

Mapping glycoside hydrolase substrate subsites by isothermal titration calorimetry

“…Thus, a change in enthalpy is compensated by an opposite change in entropy. This phenomenon, termed enthalpy-entropy compensation, has been described in many systems (36)(37)(38), however, the biological relevance of this phenomenon is a matter of debate (39)(40)(41). The seemingly linear relationship results, in fact, from the limited range of ⌬G a (K a values) used in the experiments and the Gibbs free energy relationship, ⌬G a ϭ ⌬H a Ϫ T⌬S a (see dashed lines in Fig.…”

Lectins: Tools for the Molecular Understanding of the Glycocode

“…83 This oligosaccharide represents a core branching structure in all Nlinked glycoproteins. 76 Despite the general feature of being enthalpically driven with an unfavourable entropic contribution, a few lectincarbohydrate systems show positive entropy changes. As reported in Table 2, most of the carbohydrates that bind to ECorL show negative DS, but positive entropic changes are observed for galactose, fucose, methyl-a-N-dansylgalactosaminide and 2 -fucosyllactose.…”