Solution Structures of Human Immunoglobulins IgG
and IgM and Rheumatoid Factor IgM-RF

V. V. Volkov*, R. L. Kayushina*, V. A. Lapuk**, E. V. Shtykova*, E. Yu. Varlamova***,
M. Malfois****, and D. I. Svergun*****

* Shubnikov Institute of Crystallography, Russian Academy of Sciences,
Leninski pr. 59, Moscow, 119333 Russia

e-mail: vvo@ns.crys.ras.ru

** Zelinski Institute of Organic Chemistry, Russian Academy of Sciences,
Leninski pr. 47, Moscow, 119991 Russia

*** Hematology Research Center, Russian Academy of Medical Sciences,
Novozykovski proezd 4a, Moscow, 125167 Russia

**** Netherlands Organization for Scientific Research, Grenoble, France

***** European Molecular Biology Laboratory, c/o DESY, Notkestrasse 85, Hamburg, 22603 Germany

Received July 1, 2002

Abstract—The low-resolution structures of human immunoglobulins M (IgM) and G (IgG) and the rheumatoid
factor (IgM-RF) in solution were determined from synchrotron-radiation small-angle X-ray scattering by the
method of dummy atom modeling (bead models). The structural models of IgM determined on the assumption
that the molecule has a fivefold symmetry axis are in good agreement with the atomic structure of this protein
proposed earlier. The molecular structure of the rheumatoid factor IgM-RF reconstructed by dummy atom mod-
eling differs from the model of the IgM molecule: the F(ab)₂ regions in the IgM-RF pentamer are asymmetric.
This result confirms the earlier assumption that these regions in IgM-RF are different both structurally and bio-
chemically. The typical shape of the IgG molecule in solution was demonstrated to be closer to the Y type, with
the maximum size being larger than the size of the known crystallographic models. © 2003 MAIK
“Nauka/Interperiodica”.

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