Bis azo dyes--studies on the mechanism of complex formation with IgG modulated by heating or antigen binding.

The mechanism of binding of azo dyes (bis azo) to immunoglobulin G of altered conformation, induced by heating or interaction with antigen was analysed in this work. Azo dyes: Congo Red, Evans Blue and Trypan Blue were selected for these studies. The molecules of Congo Red and Evans Blue associate readily in water and exist as polymolecular micellar species of liquid crystalline organization. Such organization of molecules appeared necessary for these dyes to interact with antibodies and to affect the formation of immune complex. It was proved by studying the properties of isomeric dyes Evans Blue and Trypan Blue, whose ability to form polymolecular conglomerates in water differs, being high for Evans Blue and low for Trypan Blue. The dyes seem to influence the formation of the immune complex generally by interacting with individual immunoglobulin molecules. The rate of exchange of dye molecules in conglomerate bound to protein varies and is the lowest for the portion of molecules which are engaged directly in the complex with protein. Electron microscopic studies also confirmed the polymolecular form of the dye in the dye-protein complex. The computational simulation of dye-dye and dye-protein interaction was performed in a model system. The micelle in the system was represented by three molecules of Congo Red. The peptide loop composed of amino acids 68-88 originating from VL IgG domain, was selected to represent protein. Amino acid side chains of this fragment were reduced to C beta. The best fitness was found for peptide chains of twisted beta conformation and independently optimized conformation of the dye in a form of "twisted ribbon" micelle. It was concluded that the IgG domains become accessible for penetration of the dye after being relaxed in the result of heating or interaction with the antigen.