Dynamical structure of the hinge region of immunoglobulin G as studied by 13C nuclear magnetic resonance spectroscopy.

The segmental flexibility of the hinge region of immunoglobulin G (IgG) molecules has been considered to play important roles in the mediation between antigen recognition and effector functions. Here we report the result of a 13C nuclear magnetic resonance study of the dynamical structure of the hinge region of a mouse monoclonal IgG2a antibody. In the present work, a variety of IgG2a analogs selectively labeled with 13C at the carbonyl carbon atom were prepared. The flexibility of the hinge region was discussed on the basis of the linewidth data of 13C resonances obtained using a Carr-Purcell-Meiboom-Gill pulse train. It was concluded that the hinge region of the mouse IgG2a molecule has a mosaic structure with heterogeneous nature of flexibility with the rigid core part flanked by upper and lower hinges, which are highly flexible peptide segments. Cleavage of the inter-chain disulfide bridges led to homogeneous flexibility of the hinge region, except for the N-terminal side of the upper hinge. It was suggested that the rigidity in the N-terminal side of the upper hinge is due to the interaction with the CH1 domain. Biological significance of the mosaic structure of the hinge region was briefly discussed.