| Research Abstract |
We developed stable-isotope-assisted NMR strategies for structural analyzes of big systems in order to elucidate molecular mechanisms of signal transduction of multi-functional proteins. This project was mainly aimed at elucidation of the principles for the constructions of the functional sites in immunoglobulin molecules especially responsible for antigen recognition, effector functions, and the mediation of both functions.
1. Binding sites on IgG molecules of a variety of ligands, e.g., antigens and bacterial IgG-binding proteins, were identified. Conformations of the ligands in the complexes were determined.
2. Conformational changes of IgG molecules induced upon ligand-binding were detected on the basis of the chemical shift data. Dynamical structures of the antigen-binding sites were revealed on the basis of the H-D exchange and the relaxation data.
3. On the basis of the ^<13>C NMR data, it was revealed that the hinge region of IgG has a mosaic structure with a heterogeneous nature of flexibility. This flexibility allows the Fc portion to be mobile even in huge immune complexes.
4. By use of an IgG mutant that lacks the N-linked oligosaccharides attached to thd Fc portion, it was revealed that these sugar chains have crucial roles in the construction of local structures in the C_H2 domain that are responsible for expression of the effector functions.
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