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 β-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.