Multivalent Interactions of Polyamide Based Sequence-Controlled Glycomacromolecules with Concanavalin A.

Binding of mannose presenting macromolecules to the protein receptor concanavalin A (ConA) is investigated by means of single-molecule atomic force spectroscopy (SMFS) in combination with dynamic light scattering and molecular modeling. Oligomeric (M ≈ 1.5-2.5 kDa) and polymeric (M ≈ 22-30 kDa) glycomacromolecules with controlled number and positioning of mannose units along the scaffolds accessible by combining solid phase synthesis and thiol-ene coupling are used as model systems to assess the molecular mechanisms that contribute to multivalent ConA-mannose complexes. SMFS measurements show increasing dissociation force from monovalent (≈57 pN) to pentavalent oligomers (≈75 pN) suggesting subsite binding to ConA. Polymeric glycomacromolecules with larger hydrodynamic diameters compared to the binding site spacing of ConA exhibit larger dissociation forces (≈80 pN), indicating simultaneous dissociation from multiple ConA binding sites. Nevertheless, although simultaneous dissociation of multiple ligands could be expected for such multivalent systems, predominantly single dissociation events are observed. This is rationalized by strong coiling of the macromolecules' polyamide backbone due to intramolecular hydrogen bonding hindering unfolding of the coil. Therefore, this study shows that the design of glycopolymers for multivalent receptor binding and clustering must consider 3D structure and intramolecular interactions of the scaffold.