Probing Scaffold Size Effects on Multivalent Lectin-Glycan Binding Affinity, Thermodynamics and Antiviral Potency Using Polyvalent Glycan-Gold Nanoparticles

Multivalent lectin-glycan interactions (MLGIs) are pivotal for viral infections and immune regulation. Their structural and biophysical data are thus highly valuable, not only for the understanding of basic mechanisms but also for designing potent glycoconjugate therapeutics against target MLGIs. However, such information for some important MGLIs remain poorly understood, which has greatly limited the research progress in this area. We have recently developed densely glycosylated nanoparticles (e.g., ~4 nm quantum dot (QD) or ~5 nm gold nanoparticle (GNP)) as new mechanistic probes for MLGIs. Using two important tetrameric viral receptors, DC-SIGN and DC-SIGNR as model lectins, we have shown these probes not only can offer sensitive fluorescence readouts for MLGI affinity quantification, but also reveal key structural information (e.g., binding site orientation and binding mode) that are very useful for MLGI targeting. However, the relatively small sizes of scaffolds may not be optimal for maximizing MLGI affinity and targeting specificity. Herein, using -manno-1,2-biose (DiMan) functionalized GNPs (GNP-DiMan) probes, we have systematically studied how GNP scaffold size (e.g., 5, 13, and 27 nm) and glycan density (e.g., 100, 75, 50 and 25%) determine their MLGI affinities, thermodynamics, and antiviral properties. We have developed a new GNP fluorescence quenching assay format for quantifying MLGI affinity to minimize the potential interference from GNP’s strong inner filter effect, revealing that increasing GNP size is highly beneficial to enhance MLGI affinity. We have further determined the MLGI thermodynamics by combining temperature-dependent affinity measurement and Van’t Hoff analysis, revealing that GNP-DiMan-DC-SIGN/R binding is enthalpy driven. Finally, we find that increasing GNP size significantly enhances the antiviral potency. Notably, the DiMan functionalised 27 nm GNP (G27-DiMan) potently and robustly blocks both DC-SIGN and DC-SIGNR mediated pseudo-Ebola virus cellular entry with an EC50 of ~23 and ~49 pM, respectively, placing it the most potent glycoconjugate entry inhibitor against DC-SIGN/R mediated Ebola cellular infections.