Background: Frequently observed structural deviations of myeloma-derived immunoglobulins affect polypeptide chain packing and domain stability, enhancing their tendency to aggregate, with all the clinical consequences. Congo red complexation with myeloma immunoglobulins is proposed in this work as a general test to disclose the instability of these proteins. The large ribbon-like supramolecular ligands of Congo red form complexes with proteins by adhesion to beta-conformation polypeptide chains, if allowed to make contact with their backbone interfaces. This can occur in the case of myeloma-derived immunoglobulins with deficient polypeptide chain packing.
Material/methods: Specially adapted two-dimensional agarose electrophoresis of serum proteins, which allows the transient contact of Congo red and serum proteins during migration, was used to reveal the presence of protein components amenable to ligand penetration and binding. The combination of electrophoresis and Congo red binding to proteins permits the removal of loosely attached dye and evaluation of the effective complexation properties of the immunoglobulin fraction directly in the serum.
Results: Comparative studies of dye complexation with two L chains having different reactivities with Congo red confirmed that dye binding depended on protein instability in the conditions used. Myeloma proteins revealed different binding capabilities in the test used here.
Conclusions: The complexes formed by the supramolecular dye Congo red with myeloma immunoglobulins differ in stability. Those of high stability indicate the abnormal protein structure thought to produce clinical symptoms. This work proposes an easy technique to differentiate the stability of complexes.