(1) its binding 𝐾 𝑑 was roughly the same as that of DC-SIGN (e.g. 1.6 ± 0.3 vs. 1.54 ± 0.07 nM), which is >20 fold lower (stronger) than that of DC-SIGNR (35 ± 2 nM) (Fig. ; Table ); (2) its maximum FRET ratio (F max ) was also comparable to that of DC-SIGN, which is >2 fold that of DC-SIGNR despite the PQR of the latter being 10 times that of the former (Fig. ; Table ); (3) binding of DC-SIGN-C with QD-DiMan yielded a QD-protein complex that has a similar Dh to that of DC-SIGN, which is much smaller than that of DC-SIGNR (SI, Fig. ). These results suggest that DC-SIGN-C still adopts the mode of simultaneous tetravalent binding similar to that of DC-SIGN, rather than the inter-crosslinking mode of binding observed for DC-SIGNR. This result indicates that the C-terminal segment is not directly responsible for the specific CRD orientation, and thus distinct binding modes, of DC-SIGN and DC-SIGNR. This is consistent to a previous report showing that the HIV-1 virus only bound to DC-SIGN and not DC-SIGNR, and removal of the C-terminal segment in DC-SIGN did not demolish its viral transmission, although its binding affinity to cell surface ICAM-3 and HIV-1 transmission efficiency were both reduced. Despite close similarities between DC-SIGN-C and DC-SIGN in QD-DiMan binding at 20 o C, their binding temperature dependencies are drastically different. While the 𝐾 𝑑 for DC-SIGN-QD-DiMan binding is increased roughly 4 fold (i.e. affinity is weakened 4 fold) as temperature is increased from 20 to 30 o C, the 𝐾 𝑑 of DC-SIGN-C remains essentially unchanged. Moreover, the maximum FRET ratio for DC-SIGN binding was found to remain almost constant, while that of DC-SIGN-C was decreased considerably with increasing temperature (Fig. and). The Van 't Hoff plot of DC-SIGN-C-QD-DiMan binding therefore shows little change in the ln(𝐾 𝑑 ) with changing 1/T, and the binding ∆𝐻 and -𝑇∆𝑆 (at 298 K) terms are obtained to be 2±4 and -52±3 kJ mol -1 , respectively. This thermodynamic profile contrasts greatly with that of DC-SIGN-QD-DiMan binding (∆𝐻 = -96.8 ± 0.6 and -𝑇∆𝑆 = 48.1 ± 0.6 kJ mol -1 ) or DC-SIGNR (∆𝐻 = -100 ± 10 and -𝑇∆𝑆 = 60 ± 10 kJ mol -1 ). Therefore the removal of the C-terminal segment in DC-SIGN has shifted the MLGI from being enthalpy driven (for DC-SIGN) to entropy driven (for DC-SIGN-C) without changing the lectin's multivalent binding mode. Here, the highly favorable binding enthalpy observed in DC-SIGN (-97 kJ mol -1 ) is diminished completely in DC-SIGN-C (~2 kJ mol - 1 ), but the binding is compensated with a strongly favorable entropy term (-𝑇∆𝑆 = -52 ± 3 kJ mol -1 ), giving rise to almost the same overall binding G (e.g. -49 ± 1 vs. -50 ± 5 kJ mol -1 for DC-SIGN vs. DC-SIGN-C at 298 K, see Table and Fig. ).