The binding thermodynamic parameters for QD-DiMan binding with DC-SIGN/R were summarized in Table . Based on these data, two conclusions can be drawn. ). Given that glycan binding does not lead to conformational changes in CRD, and the QD-OH control without the terminal DiMan shows no measurable binding with DC-SIGN (SI, Fig. ), these results suggest that all four CRDs in DC-SIGN/R must have engaged in glycan binding as expected for enthalpy driven MLGIs. The excellent consistency between the H values measured here and that measured from ITC thus confirms our QD-FRET technique as a valid, sensitive new method for investigating the binding thermodynamics of MLGIs. (2) The multivalent binding entropy contributions (-TS) for DC-SIGN/R-QD-DiMan are ~5.7 and ~7 times that of the monovalent DC-SIGN CRD-DiMan binding measured by ITC (8.5 kJ mol -1 at 298 K), respectively. Thus a larger entropy penalty for DC-SIGNR binding with QD-DiMan is responsible for its lower binding affinity compared to DC-SIGN. The total entropy change of multivalent interactions consists of changes in translational and rotational entropies of binding partners as well as entropy changes associated with the surrounding water molecules upon association. It also includes entropy changes from binding induced conformational changes. Given that all four CRDs in DC-SIGN/R are engaged in glycan binding and each CRD most likely accommodates a single DiMan molecule, entropic contributions from conformation change of monovalent CRD-DiMan binding should be very similar for both lectins. Therefore, the higher entropic penalty observed for DC-SIGNR over DC-SIGN upon binding with QD-DiMan is most likely due to a greater reduction of translational and rotational degrees of freedom by forming a smaller number of larger inter-cross-linked protein-QD complexes. The thermodynamic parameters obtained here are fully consistent with what is expected for MLGIs with different binding modes (i.e. simultaneous binding v.s. inter-crosslinking).