A quercetin-based flavanoid (rutin) reverses amyloid fibrillation in ß-lactoglobulin at pH 2.0 and 358 K.

ß-lactoglobulin (BLG) is a well characterized milk protein and a model for folding and aggregation studies. Rutin is a quercetin based-flavanoid and a famous dietary supplement. It is a potential protector from coronary heart disease, cancers, and inflammatory bowel disease. In this study, amyloid fibrillation is reported in BLG at pH 2.0 and temperature 358 K. It is inhibited to some extent by rutin with a rate of 99.3 h-1 M-1. Amyloid fibrillation started taking place after 10 h of incubation and completed near 40 h at a rate of 16.6 × 10-3 h-1, with a plateau during 40-108 h. Disruption of tertiary structure of BLG and increased solvent accessibility of hydrophobic core seem to trigger intermolecular assembly. Increase in 7% ß-sheet structure at the cost of 10% α-helical structures and the electron micrograph of BLG fibrils at 108 h further support the formation of amyloid. Although it could not block amyloidosis completely, and even the time required to reach plateau remains the same, a decrease of growth rate from 16.6 × 10-3 to 13.5 × 10-3 h-1 was observed in the presence of 30.0 µM rutin. Rutin seems to block solvent accessibility of the hydrophobic core of BLG. A decrease in the fibril population was observed in electron micrographs, with the increase in rutin concentration. All evidences indicate reversal of fibrillation in BLG in the presence of rutin.

Different conformational states of hen egg white lysozyme formed by exposure to the surfactant of sodium dodecyl benzenesulfonate.

The aim of this study was to investigate the effects of sodium dodecyl benzenesulfonate (SDBS) on hen egg white lysozyme (HEWL) fibrillogenesis at pH 7.4. HEWL fibrillogenesis in the presence of SDBS was characterized using several spectroscopic techniques (turbidity, light scattering, intrinsic fluorescence, ThT binding assay, ThT kinetics, far-UV CD, and transmission electron mmicroscopy). The turbidity and light scattering data revealed that SDBS induces aggregation in HEWL in dose-dependent manner. HEWL aggregation was seen at low SDBS concentrations (0.03 to 0.5 mM) but it was not observed at concentrations of SDBS at >0.6 mM. The ThT and TEM data clearly showed that the aggregates formed in the presence of SDBS had an amyloid-like morphology. From the CD analysis it was clear that low SDBS concentrations decreases the α-helical content while the ß-sheet content increased. As the SDBS concentration further increased, the α-helical content increased again. The ThT kinetics analysis revealed that the HEWL monomer directly converted into the amyloid fibril without lag phase. All the spectroscopic and microscopic results support the finding that low concentrations of SDBS stimulate fibrillogenesis in HEWL, and that no fibrillogenesis occurs at higher SDBS concentrations.

Allura red rapidly induces amyloid-like fibril formation in hen egg white lysozyme at physiological pH.

Allura red (AR) is an artificial azo dye mostly used in food industries and has potential health risks. We examined the role of AR in amyloidogenesis using hen egg white lysozyme (HEWL) at pH 7.0. The amyloidogenic induction properties of AR in HEWL were identified by circular dichroism (CD), turbidity, intrinsic fluorescence, light scattering, transmission electron microscopy (TEM), and molecular dynamic simulation studies. Turbidity and light scattering measurements showed that HEWL becomes aggregated in the presence of 0.03-15.0 mM of AR at pH 7.0 but not at very low AR concentrations (0.01-0.28 mM). However, AR-induced aggregation is a kinetically rapid process, with no observable lag phase and saturation within 6 s. The kinetics results suggested that the HEWL aggregation induced by AR is very rapid. The CD results demonstrated that the total ß-sheet content of HEWL was increased in the AR treated samples. The TEM results are established that AR-induced aggregates had amyloid-like structures. Molecular dynamics simulations analysis showed that the bound AR-HEWL structures were highly favored compared to unbound structures. The mechanism of AR-induced amyloid fibril formation may involve electrostatic, hydrogen bonding, and hydrophobic interactions.