Development of a Glycoconjugate Tool Set for the Assembly and Presentation of Carbohydrate Ligands on Surfaces

Carbohydrate and protein interactions are often essential in viral and bacterial infection, the immune response, cell differentiation and development, and the progression of tumor cell metastasis. Therefore, an understanding of carbohydrate–protein interactions at the molecular level would lead to a better insight into the biological process of living systems and assist in the development of therapeutic and diagnostic strategies. Our goal was to synthesize different mannose derivatives, immobilize them on nano-patterned surfaces and carry out binding studies with mannose-binding lectins in order to characterize carbohydrate–protein interactions.

Different derivatives of D-mannose (monosaccharide, (1→2)-linked disaccharide, (1→3)-linked disaccharide, and (1→2, 1→3)-linked trisaccharide) with tethered –SH groups were synthesized. Alkyne-terminated D-mannose derivatives were synthesized to be immobilized via click chemistry on azide-functionalized glass slides. These molecules were constructed by glycosylation of appropriately protected glycosyl donors and acceptors, followed by free-radical addition to introduce the thiol terminals onto the aglycons. Subsequent deprotection afforded the corresponding free-OH saccharides. Standard robotic microarray printing technology was used to couple these thiol-terminated aglycons to epoxide-functionalized glass slides.

Using a fluorescence scanner, binding between carbohydrates and Con A were quantified and processed to obtain dissociation constants (K_D). The (1→2)-linked disaccharide 18 showed highest binding with Con A with dissociation constant of 58 nM [nano molar]. The (1→3)-linked disaccharide 24 had a dissociation constant of 68 nM [nano molar] with Con A. The differences in binding constants seem to be greater at higher concentrations above 400 μM [micro molar]. The monosaccharide 5 had an average surface dissociation constant of 76 nM [nano molar] and 91 nM [nano molar] for the trisaccharide 29. In general, the disaccharides 18 and 24 showed enhanced binding interaction with Con A than the monosaccharide 5 and trisaccharide 29.