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Changes in the microenvironment of Trp in lysozyme are one of the key factors in the fibrillation process. Gallic acid through the oxidation of o-dhydroxy moiety into quinone was shown to inhibit lysozyme fibrillation by stabilizing the Trp microregions [Konar et al., Int. J. Biol. Macromol. 103 (2017) 1224–1231]. In this article we compare the inhibitory effects of several gallic acid-based phenolic compounds. The results show that pyrogallol, and 3,4-dihydroxy benzoic acid, each containing the o-dihydroxy moiety exhibited a significant inhibitory effect on lysozyme fibrillation which is further supported by docking studies. Interestingly, the inhibitory effect of pyrogallol is almost similar to that observed for gallic acid. The lower inhibitory effect of 3,5-dihydroxy benzoic acid and 4-hydroxy benzoic acid corroborates this finding as neither of the compounds can be transformed into quinone intermediates. The ineffectiveness of benzoic acid towards fibrillation questions the role of the COOH group in the inhibition. The IC20 values determined show the similar trends. Results of the Thioflavin T binding assay and parameters from the docking studies reveal a strong correlation based on which a relation has been obtained that could be used to identify potential polyphenol based inhibitors by considering docking studies alone.

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.