Abstract
Amyloid light chain (AL) amyloidosis is a protein misfolding disease where immunoglobulin light chains sample partially folded states that lead to misfolding and amyloid formation, resulting in organ dysfunction and death. In vivo, amyloid deposits are found in the extracellular space and involve a variety of accessory molecules, such as glycosaminoglycans, one of the main components of the extracellular matrix. Glycosaminoglycans are a group of negatively charged heteropolysaccharides composed of repeating disaccharide units. In this study, we investigated the effect of glycosaminoglycans on the kinetics of amyloid fibril formation of three AL cardiac amyloidosis light chains. These proteins have similar thermodynamic stability but exhibit different kinetics of fibril formation. We also studied single restorative and reciprocal mutants and wild type germ line control protein. We found that the type of glycosaminoglycan has a different effect on the kinetics of fibril formation, and this effect seems to be associated with the natural propensity of each AL protein to form fibrils. Heparan sulfate accelerated AL-12, AL-09, κI Y87H, and AL-103 H92D fibril formation; delayed fibril formation for AL-103; and did not promote any fibril formation for AL-12 R65S, AL-103 delP95aIns, or κI O18/O8. Chondroitin sulfate A, on the other hand, showed a strong fibril formation inhibition for all proteins. We propose that heparan sulfate facilitates the formation of transient amyloidogenic conformations of AL light chains, thereby promoting amyloid formation, whereas chondroitin sulfate A kinetically traps partially unfolded intermediates, and further fibril elongation into fibrils is inhibited, resulting in formation/accumulation of oligomeric/protofibrillar aggregates.
Highlights
Proteins Selected in This Study; Secondary Structure and Thermodynamic Stability of Amyloid light chain (AL) Proteins—For this study, restorative and reciprocal mutants have been selected to understand the effect of specific amino acids in the fibril formation properties of these proteins in the presence of different glycosaminoglycans
We chose the restorative mutant AL-09 H87Y because it regains most of the thermodynamic stability found in the nonamyloidogenic germ line I O18/O8, whereas it significantly delays fibril formation compared with its parent protein AL-09
The double restorative mutant AL-09 I34N/H87Y increases the thermodynamic stability slightly beyond that of I O18/O8 and has a larger delay in fibril formation compared with I O18/O8 [32], suggesting that Ile-34 and His-87 play an important role in the amyloid formation process for AL-09
Summary
Results: Fibrillation of AL proteins was accelerated by heparan sulfate and inhibited by chondroitin sulfate A. Conclusion: Endogenous GAGs can modulate amyloid formation, and their effect is determined by the amyloidogenic properties of AL proteins studied. We investigated the effect of glycosaminoglycans on the kinetics of amyloid fibril formation of three AL cardiac amyloidosis light chains. These proteins have similar thermodynamic stability but exhibit different kinetics of fibril formation. We propose that heparan sulfate facilitates the formation of transient amyloidogenic conformations of AL light chains, thereby promoting amyloid formation, whereas chondroitin sulfate A kinetically traps partially unfolded intermediates, and further fibril elongation into fibrils is inhibited, resulting in formation/accumulation of oligomeric/protofibrillar aggregates
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