Significant other half of a glycoconjugate: contributions of scaffolds to lectin-glycoconjugate interactions

The glycan epitopes of natural and synthetic glycoconjugates exist as covalent attachments of well-defined inner structures or scaffolds. Macromolecules such as proteins, peptides, lipids, and saccharides and synthetic structures serve as scaffolds of glycoconjugates. It is generally perceived that the biological activities of glycoconjugates are determined mainly by the attached glycans, while the seemingly inert inner scaffolds play a passive role by providing physical support to the attached glycan epitopes. However, our data show that scaffolds actively influence lectin recognition and can potentially modulate lectin-mediated signaling properties of glycoconjugates. Through in vitro experiments, we found that the scaffolds significantly altered the thermodynamic binding properties of the covalently attached glycan epitopes. When a free glycan was attached to a scaffold, its lectin binding entropy became more positive. The level of positive entropic gain was dependent on the types of scaffolds tested. For example, protein scaffolds of glycoproteins were found to generate more positive entropy of binding than synthetic scaffolds. Certain scaffolds were found to have limiting effects on glycoconjugate affinity. We also found that scaffold-bearing glycans with a similar affinity or an identical valence demonstrated different kinetics of lattice formation with lectins, when the scaffold structures were different. Our data support the view that scaffolds of glycoconjugates (i) help the covalently attached glycans become more spontaneous in lectin binding and (ii) help diversify the lattice forming or cross-linking properties of glycoconjugates.