Polyvalent binding to carbohydrates immobilized on an insoluble resin

Abstract

Numerous studies have established that polyvalency is a critical feature of cell surface carbohydrate recognition. Nevertheless, carbohydrate-protein interactions are typically evaluated by using assays that focus on the behavior of monovalent carbohydrate ligands in solution. It has generally been assumed that the relative affinities of monovalent carbohydrate ligands in solution correlate with their polyvalent avidities. In this paper we show that carbohydrate ligands synthesized directly on TentaGel beads interact with carbohydrate-binding proteins in a polyvalent manner. The carbohydrate-derivatized beads can, therefore, be used as model systems for cell surfaces to evaluate polyvalent carbohydrate-protein interactions. By using a combinatorial approach to synthesize solid-phase libraries of polyvalent carbohydrates, one can rapidly address key issues in the area of cell surface carbohydrate recognition. For example, studies reported herein demonstrate that there is an unanticipated degree of specificity in recognition processes involving polyvalent carbohydrates. However, the correlation between polyvalent avidities and solution affinities is poor. Apparently, the presentation of carbohydrates on the polymer surface has a profound influence on the interaction of the ligand with the protein receptor. These findings have implications for how carbohydrates function as recognition signals in nature, as well as for how polyvalent carbohydrate-protein interactions should be studied.

Figure 1

Synthesis of the resin-bound disaccharide Galβ1,3GalNAcβSPh. T, TentaGel resin. Conditions were as follows: a, HOBt/HBTU, DIEA, NMP, room temperature, 12 h; b, NH₂NH₂/DMF (1:7), room temperature, 9 h; c, trifluoromethanesulfonic anhydride, DTBMP, CH₂Cl₂, −60°C to 0°C; repeat; d, thiolacetic acid, room temperature, 27 h; e, 20% trifluoroacetic acid/CH₂Cl₂, room temperature, 30 min; and f, LiOH, 80% MeOH/tetrahydrofuran, room temperature, 11 h.

Figure 2

Aggregation study of TentaGel beads. (A) Underivatized beads did not aggregate when treated with Arachis hypogaea lectin at 25 μg/ml. (B) Derivatized beads aggregated under the same conditions. (×100.)

Figure 3

Colorimetric assay of the four-carbohydrate mixture. (×100.)