Correlation between the structure of IgG and its Fc-fragment and their ability to interact with staphylococcal protein A

Interaction between 7S monomers of rabbit IgG, dimers of molecules of this protein, IgG with disulfide bond ruptured in the hinge region of the molecule, and various fragments of IgG molecules, on the one hand, and protein A ofStaphylococcus aureus, on the other hand, were investigated by the passive hemagglutination inhibition test. Only the Fc-fragment of the rabbit IgG molecule obtained with papain was shown to bind protein A. Activity of the Fc-fragment on a molar basis was shown to be only one-sixth of that of native IgG. After repair of the disulfide bond between the chains in the hinge region of the IgG molecule, its ability to bind protein A was reduced by two-thirds. The binding activity of IgG was increased on a molar basis twelvefold as a result of its spontaneous dimerization. It is concluded from the results that the structural organization of the Fc-fragment of the IgG molecule correlates with its ability to interact with protein A.Laboratory of Immunochemistry, N. F. Gamaleya Institute of Epidemiology and Microbiology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR P. A. Vershilova.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 89, No. 3, pp. 318–320, March, 1980.