Millimolar concentration of sodium dodecyl sulfate inhibit thermal aggregation in hen egg white lysozyme via increased α-helicity

Abstract

The objective of this study was to assess the effects of sodium dodecyl sulphate (SDS) on the hen egg white lysozyme (HEWL) at pH 9.0. We employed several spectroscopic (light scattering, intrinsic fluorescence, dynamic light scattering (DLS), and circular dichroism (CD)) techniques to evaluate the role of SDS in prevention of aggregation and imparting stability to HEWL. From the spectroscopic measurements, it was observed that the secondary as well as tertiary structures were modified in the presence of SDS. Thermal stability of HEWL with or without SDS was also evaluated. In the absence of SDS, HEWL starts unfolding at transition temperature 54.0 ± 0.22 °C. However, in the presence of 2.0 mM SDS, the HEWL unfolded at slightly higher temperature, and transition temperature was found to be around 59.77 ± 0.27 °C. In this study, we also found that thermal unfolding of HEWL led to simultaneous aggregation at temperatures above 55 °C as confirmed by light scattering measurements but no aggregation was seen in the presence of SDS. In the absence of SDS, the hydrodynamic radii of HEWL increased at higher temperature. However, the hydrodynamic radii remained unchanged in the presence of SDS up to 90 °C. The overall results suggested that SDS provided extra stability to and simultaneously prevented aggregation of HEWL. The possible interactions found in SDS-stabilized HEWL are electrostatic and hydrophobic.