The effects of sodium sulfate, glycosaminoglycans, and Congo red on the structure, stability, and amyloid formation of an immunoglobulin light-chain protein

Light-chain amyloidosis (AL) is characterized by immunoglobulin light-chain fragments aggregating into amyloid fibrils that deposit extracellularly in vital organs such as the kidney, the heart, and the liver, resulting in tissue degeneration and organ failure, leading to death. Cardiac involvement is found in 50% of AL patients and presents the most severe cases with a life expectancy of less than a year after diagnosis. In this study, we have characterized the variable domain of a cardiac AL patient light chain called AL-09. AL-09 folds as a beta-sheet and is capable of forming amyloid fibrils both in the presence of sodium sulfate and in self-seeded reactions under physiological conditions. Glycosaminoglycans such as dermatan sulfate and heparin promote amyloid formation of self-seeded AL-09 reactions, while the glycosaminoglycan chondroitin sulfate A stabilized oligomeric intermediates and did not elongate the preformed fibrils (nucleus) present in the reaction. Finally, the histological dye Congo red, known to bind to the cross beta-sheet structure of amyloid fibrils, inhibits AL-09 amyloid fibril formation in the presence of sodium sulfate and in self-seeded reactions. This paper provides insight into the impact of different reagents on light-chain stability, structure, amyloid fibril formation, and inhibition.