Gallic acid induced dose dependent inhibition of lysozyme fibrillation

Amyloidosis is primarily characterized by the deposition of misfolded protein aggregates. Although the natural polyphenols have long been known as effective amyloid inhibitors, the mechanistic details of their inhibitory actions still remain unclear. Our present study explores the inhibition mechanism of polyphenols by studying the anti-amyloidogenic property of gallic acid (GA), the smallest structural unit of tea polyphenols, on hen egg white lysozyme (HEWL) at physiological pH. Using various spectroscopic techniques such as UV-vis, fluorescence, circular dichroism and dynamic light scattering, and microscopic techniques such as TEM and FESEM, it has been shown that GA potentially inhibits the self-aggregation process in a concentration dependent manner. Gel electrophoresis studies suggest that the o-dihydroxy moiety of GA is oxidized into the quinone moiety and H₂O₂ in the system under the experimental conditions. The quinone binds near the hydrophobic region of HEWL and restricts hydrophobic exposure. Cyclic voltammetry studies reveal that the Met residues of HEWL are oxidized by H₂O₂ to highly polar sulfoxide-modified side chains. The partially unfolded intermediates formed under the denaturing conditions employed remain in contact with the solvent thus preventing further aggregation.