[Theoretical and experimental studies on the conformation of the hinge regions in human immunoglobulin G subclasses]

Using the methods of difference adiabatic scanning microcalorimetry and difference thermal perturbation spectrophotometry it was established that both the Fc subunits within the intact immunoglobulins G of different subclasses, and the Fc fragments corresponding to them significantly differ in conformational properties. These differences are associated with a different energy of interactions between the CH2 and CH3 domains and also with a different rigidity of structure of the N- and C-terminal parts of the CH2 domains. The analysis of these data allowed to suggest that the "hinge region" interacts with the CH2 domains and the difference in the structure of this region affect the conformation of the Fc subunits. Possible models of the "hinge regions" in immunoglobulins G of the first, second and fourth subclasses, and also their arrangement relative to the CH2 domains were proposed. The analysis of curves of the small-angle scattering of X-rays shows an agreement between the theoretical models and experimental data.