Probing Carbohydrate-Lectin Recognition in Heterogeneous Environments with Monodisperse Cyclodextrin-Based Glycoclusters

A series of beta-cyclodextrin (beta CD)-scaffolded glycoclusters exposing heterogeneous yet perfectly controlled displays of alpha-mannosyl (alpha-Man) and beta-lactosyl (beta-Lact) antennas were synthesized to probe the mutual influence of varying densities of the saccharide motifs in the binding properties toward different plant lectins. Enzyme-linked lectin assay (ELLA) data indicated that the presence of beta-Lact residues reinforced binding of alpha-Man to the mannose-specific lectin concanavalin A (Con A) even though homogeneous beta-Lact clusters are not recognized at all by this lectin, supporting the existence of synergic recognition mechanisms (heterocluster effect). Conversely, the presence of alpha-Man motifs in the heteroglycoclusters also resulted in a binding-enhancing effect of beta-Lact toward peanut agglutinin (PNA), a lectin strongly binding multivalent lactosides but having no detectable affinity for alpha-mannopyranosides, for certain architectural arrangements. Two-site, sandwich-type ELLA data corroborated the higher lectin clustering efficiency of heterogeneous glycoclusters compared with homogeneous displays of the putative sugar ligand with identical valency. A turbidity assay was also consistent with the previous observations. Most revealingly, the lectin cross-linking ability of heterogeneous glycoclusters was sensitive to the presence of high concentrations of the non-ligand sugar, strongly suggesting that "mismatching" saccharide motifs may modulate carbohydrate-lectin specific recognition in a lectin-dependent manner when present in highly dense displays together with the "matching" ligand, a situation frequently encountered in biological systems.