Stoichiometry and Thermodynamics of the Interaction between the Fc Fragment of Human IgG1 and Its Low-Affinity Receptor FcγRIII

Abstract

IgG-Fc receptors, cell surface glycoproteins binding the Fc region of antibodies, play a crucial role in the immune system. To better understand the nature of the recognition process, we have examined the interaction between huIgG1-Fc and a soluble fragment of huFcγRIII (sCD16). Analytical ultracentrifugation experiments clearly demonstrate that IgG1-Fc and sCD16 interact weakly to form a 1:1 complex with an association constant of 1.7 x 105 M-1 in PBS at 22.0 °C. The thermodynamic parameters, obtained from the temperature dependence of the equilibrium binding constants, exhibit an enthalpy-entropy compensation with a favorable enthalpy at physiological temperatures. The value of -360 cal mo..