Dynamics of amyloid-like aggregation and gel formation of hen egg-white lysozyme in highly concentrated ethanol solution

Abstract

We investigated the mechanisms of amyloid-like aggregation and gel formation in hen egg-white lysozyme (HEWL) in a mixed solvent comprising 90% v/v ethanol in water using dynamic light scattering (DLS) and circular dichroism CD. The mechanism of HEWL in ethanol aqueous solution is interpreted into three stages as: (I) denaturation of HEWL; (II) elongation of amyloid fibrils composed of β-sheet-rich HEWL by lateral aggregation; and (III) gel formation due to the creation of junctions in amyloid fibrils. The transformation of sol to gel can be confirmed by: (1) the oscillation behavior and the rapid increase in the intensity of scattered light; (2) the power-law behavior of the correlation function of scattered light g⁽²⁾(t); (3) the appearance of a long-time tail in the distribution function of the decay time G(τ); and (4) the beginning of the reduction in initial amplitude in g⁽²⁾(t). The gelation rate was strongly dependent on the protein concentration. The estimated rod length of the amyloid fibrils increased significantly over time. Scanning electron microscopy (SEM) performed on the formation of fibrils in the HEWL gels revealed that the structure was highly heterogeneous, with areas characterized by dense fiber networks interspersed with loose network areas.