Cellular membrane disruption by amyloid fibrils involved intermolecular disulfide cross-linking

Accumulating evidence has strongly suggested that amyloid fibrils of protein or peptide are cytotoxic. Fibrillar species appear to lead to disruption of cell membrane structures and thereby cause cell death. In this study, human erythrocytes were used as an in vitro model to examine the disruptive effect of lysozyme fibrils on the plasma membrane. Both the protofibrils and mature fibrils induced hemolysis and aggregation of erythrocytes. Treating ghost membranes with the fibrils resulted in aggregation of membrane proteins through intermolecular disulfide cross-linking. LC-ESI-MS/MS and Western blotting analysis showed that lysozyme fragments were incorporated into the aggregates of ghost membrane proteins, which suggested that thio-disulfide exchange among lysozyme and membrane proteins was triggered when the fibrils interacted with erythrocyte membranes. Metal-ion chelators, radical scavengers, and antioxidants had no effect on the amyloid-induced disulfide cross-linking. The exposure of interior hydrophobic residues and the increased level of solvent-accessible disulfides in the lysozyme fibrils are thought to be involved in membrane disruption. These results may unveil a novel pathway for the cytotoxicity of amyloid fibrils.