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Low-resolution structures of immunoglobulins IgG, IgM and rheumatoid factor IgM-RF in solution were analyzed using synchrotron radiation small-angle X-ray scattering and the macromolecular shapes were restored ab initio from the scattering data. The shape of IgG agrees well with the distorted Y-type crystallographic model but has a swollen appearance reflecting flexibility of the molecule in solution. The structures of pentameric IgM and IgM-RF were reconstructed assuming a five-fold symmetry. The IgM displays a flat star-like shape with observable F(ab) 2 regions. The overall shape of the IgM-RF is similar to that of the IgM but with distinctly asymmetric F(ab) 2 regions. This result agrees with the earlier observed functional dissimilarity of the Fab fragments in the rheumatoid factor and points to their structural dissimilarity. Keywords:small-angle X-ray scattering; immunoglobulins; monodisperse solutions; molecular shape; structure modeling. conference papers 504 Volkov et al.

Natural catalytic antibodies are known to be autoantibodies and are found in patients with different autoimmune diseases. The production of catalytic autoantibodies against DNA is demonstrated for a number of lymphoproliferative diseases. The statistical analyses performed show that this production is related to the chronic proliferation of mature B lymphocytes and correlates with the corresponding autoimmune disorders.

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