Jul 1, 1975

Antigen-induced conformational changes in antibodies and their Fab fragments studied by circular polarization of fluorescence

Proceedings of the National Academy of Sciences of the United States of America
J SchlessingerI Pecht

Abstract

Conformational changes induced in antibody molecules and in their Fab fragments by binding of antigen were investigated by the circular polarization of the fluorescence emitted by the tryptophan residues. This property of the fluorescence is related to the asymmetry, and thus to the conformation and environment, of the emitting chromophore. Changes in the circular polarization of the fluorescence of the antibody were observed upon binding of RNase to anti-RNase, of poly(DL-alanyl)-poly(L-lysine) to antipoly(D-alanine), and of the "loop" of lysozyme, a monovalent antigenic determinant, to anti"loop." The spectral changes were observed at different antigen-antibody ratios, including high antigen excess, indicating that they are due to antigen binding and not to aggregation. The circular polarization of fluorescence also detects changes in conformation of the different Fab fragments upon binding of the corresponding antigens. These changes in conformation were, however, markedly different from those observed for the whole antibody molecules, and indicated an interaction between the Fc and Fab fragments in the antibody molecule, and probably a change in the conformation of Fc upon binding of antigen to the antibody. In contrast, th...Continue Reading

Mentioned in this Paper

Tryptophan
Antigen Binding
Binding Sites, Antibody
Aggregation
Lysozyme Test
Macromolecular Alteration
Fluorescence Spectroscopy
Plasma Protein Binding Capacity
Lysine
Fab Immunoglobulins

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