Compact, Polyvalent Mannose Quantum Dots as Sensitive, Ratiometric FRET Probes for Multivalent Protein–Ligand Interactions

A highly-efficient cap-exchange approach for preparing compact, dense polyvalent mannose-capped quantum dots (QDs) has been developed. The resulting QDs have been successfully used to probe multivalent interactions of HIV/Ebola receptors DC-SIGN and DC-SIGNR (collectively termed as DC-SIGN/R) via a sensitive, ratiometric Förster resonance energy transfer (FRET) assay. The QD probes specifically bind DC-SIGN, but not its closely related receptor DC-SIGNR, which is further confirmed by its specific blocking of DC-SIGN engagement with the Ebola virus glycoprotein. Tuning the QD surface mannose valency reveals that DC-SIGN binds more efficiently to densely packed mannosides and a FRET-based thermodynamic study reveals the binding is enthalpy driven. This work thus establishes QD-FRET as a rapid, sensitive technique for probing structure and thermodynamics of multivalent protein-ligand interactions.