Divergent Synthesis of 48 Heparan Sulfate-Based Disaccharides and Probing the Specific Sugar–Fibroblast Growth Factor‑1 Interaction

Several biological processes involve glycans, yet understanding their ligand specificities is impeded by their inherent diversity and difficult acquisition. Generating broad synthetic sugar libraries for bioevaluations is a powerful tool in unraveling glycan structural information. In the case of the widely distributed heparan sulfate (HS), however, the 48 theoretical possibilities for its repeating disaccharide call for synthetic approaches that should minimize the effort in an undoubtedly huge undertaking. Here we employed a divergent strategy to afford all 48 HS-based disaccharides from just two orthogonally protected disaccharide precursors. Different combinations and sequence of transformation steps were applied with many downstream intermediates leading up to multiple target products. With the full disaccharide library in hand, affinity screening with fibroblast growth factor-1 (FGF-1) revealed that four of the synthetic sugars bind to FGF-1. The molecular details of the interaction were further clarified through X-ray analysis of the sugar–protein cocrystals. The capability of comprehensive sugar libraries in providing key insights in glycan–ligand interaction is, thus, highlighted

Interactions That Influence the Binding of Synthetic Heparan Sulfate Based Disaccharides to Fibroblast Growth Factor‑2

Heparan sulfate (HS) is a linear sulfated polysaccharide that mediates protein activities at the cell–extracellular interface. Its interactions with proteins depend on the complex patterns of sulfonations and sugar residues. Previously, we synthesized all 48 potential disaccharides found in HS and used them for affinity screening and X-ray structural analysis with fibroblast growth factor-1 (FGF1). Herein, we evaluated the affinities of the same sugars against FGF2 and determined the crystal structures of FGF2 in complex with three disaccharides carrying <i>N</i>-sulfonated glucosamine and 2-<i>O</i>-sulfonated iduronic acid as basic backbones. The crystal structures show that water molecules mediate different interactions between the 3-<i>O</i>-sulfonate group and Lys125. Moreover, the 6-<i>O</i>-sulfonate group forms intermolecular interactions with another FGF2 unit apart from the main binding site. These findings suggest that the water-mediated interactions and the intermolecular interactions influence the binding affinity of different disaccharides with FGF2, correlating with their respective dissociation constants in solution