Disulfide-Bond Scrambling Promotes Amorphous Aggregates in Lysozyme and Bovine Serum Albumin

Disulfide bonds are naturally formed in more than 50% of amyloidogenic proteins, but the exact role of,disulfide bonds in protein aggregation is still not well-understood. The intracellular reducing agents and/or improper use of antioxidants in extracellular envirtminent can break proteins disulfide bonds, Making them unstable and prone to misfolding and aggregation. In this study, we report the effect of disulfide-reducing agent dithiothteitol (DTT) on hen egg white lysozyme (lysozyme) and bovine:serum albumin (BSA) aggregation at pH 7.2 and 37 degrees C. BSA and lysozyme proteins treated with disulfidereducing agents form very distinct amorphous aggregates as observed by scanning electron microscope. However, proteins with intact disulfide bonds were stable and did not aggregate over time. BSA and lysozyrne aggregates Show unique but measurable differences in 8-anilino-1-naphthalenesulfonic acid (ANS) and 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid (bis-ANS) fluorescence, suggesting a loose and flexible aggregate structure for lysozyme -but a more compact aggregate structure for BSA. Scrambled disulfide-bonded protein aggregates were observed by nonreducing sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) for both proteins. Similar amorphous aggregates were also generated using a nonthiol-based reducing agent, tris(2-carboxyethyL)phosphine (TCEP), at pH 7.2 and 37 degrees C. In summary, formation of distinct amorphous aggregates by disulfide-reduced BSA and lysozyme suggests an alternate pathway for protein. aggregation that may be relevant to several proteins.