Rheumatoid factors are the characteristic autoantibodies of rheumatoid arthritis, which bind to the Fc regions of IgG molecules. Here we report the crystal structure of the Fab fragment of a patient-derived IgM rheumatoid factor (RF-AN) complexed with human IgG4 Fc, at 3 ...
Rheumatoid factors are the characteristic autoantibodies of rheumatoid arthritis, which bind to the Fc regions of IgG molecules. Here we report the crystal structure of the Fab fragment of a patient-derived IgM rheumatoid factor (RF-AN) complexed with human IgG4 Fc, at 3.2 A resolution. This is the first structure of an autoantibody-autoantigen complex. The epitope recognised in IgG Fc includes the C gamma 2/C gamma 3 cleft region, and overlaps the binding sites of bacterial Fc-binding proteins. The antibody residues involved in autorecognition are all located at the edge of the conventional combining site surface, leaving much of the latter available, potentially, for recognition of a different antigen. Since an important contact residue is somatic mutation, the structure implicates antigen-driven selection, following somatic mutation of germline genes, in the production of pathogenic rheumatoid factors.
Related Citations:
Crystallization of a Complex between the Fab Fragment of a Human Immunoglobulin M (Igm) Rheumatoid Factor (Rf-an) and the Fc Fragment of Human Igg4 Sohi, M.K., Corper, A.L., Wan, T., Steinitz, M., Jefferis, R., Beale, D., He, M., Feinstein, A., Sutton, B.J., Taussig, M.J. (1996) Immunology 88: 636
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