Mechanistic Insight into Nanomolar Binding of Multivalent Neoglycopeptides to Wheat Germ Agglutinin.

Multivalent carbohydrate-protein interactions are frequently involved in essential biological recognition processes. Accordingly, multivalency is often also exploited for the design of high-affinity lectin ligands aimed at the inhibition of such processes. In a previous study (D. Schwefel et al., J. Am. Chem. Soc. 2010, 132, 8704-8719) we identified a tetravalent cyclopeptide-based ligand with nanomolar affinity to the model lectin wheat germ agglutinin (WGA). To unravel the structural features of this ligand required for high-affinity binding to WGA, we synthesized a series of cyclic and linear neoglycopeptides that differ in their conformational freedom as well as the number of GlcNAc residues. Combined evidence from isothermal titration calorimetry (ITC), enzyme-linked lectin assays (ELLA), and dynamic light scattering (DLS) revealed different binding modes of tetra- and divalent ligands and that conformational preorganization of the ligands by cyclization is not a prerequisite for achieving high binding affinities. The high affinities of the tetravalent ligands rather stem from their ability to form crosslinks between several WGA molecules. The results illustrate that binding affinities and mechanisms are strongly dependent on the used multivalent system which offers opportunities to tune and control binding processes.