Nanobiocatalyst facilitated aglycosidic quercetin as a potent inhibitor of tau protein aggregation.

Polyphenols have been suggested as potential therapeutic agents for the treatment of amyloidogenic diseases. In this work, we evaluate quercetin-rich onion extract for its ability to inhibit tau fibrillization. Considering the presence of polyphenols in multiple glycosidic and aglycosidic forms, a nanobiocatalyst-mediated approach has been used to extract quercetin from onion skins. The nanobiocatalysts facilitate greater release of quercetin compared to the use of free enzymes. Atomic force microscopy and fluorescence microscopy show that quercetin possesses a novel inhibitory character on tau-fibril aggregation. In contrast, quercetin-diglucoside does not have an inhibitory effect. Molecular Dynamics simulations reveal conformational changes in tau protein upon interaction with quercetin due to specific hydrogen bonding and hydrophobic interactions. The resulting conformational stability of tau monomer reduces propensity of the protein to aggregate. The ability of quercetin to inhibit tau fibrillization expands the paradigm for application of bioactive polyphenols.

Mechanistic insights into remodeled Tau-derived PHF6 peptide fibrils by Naphthoquinone-Tryptophan hybrids.

Intra-cellular tau protein tangles and extra-cellular ß-amyloid plaques are hallmarks of Alzheimer's disease (AD), characterized by the conversion of natively unfolded monomeric protein/peptide into misfolded ß-sheet rich aggregates. Therefore, inhibiting the aggregation cascade or disassembling the pre-formed aggregates becomes a pivotal event in disease treatment. In the present study, we show that Naphthoquinone-Tryptophan hybrids, i.e., NQTrp and Cl-NQTrp significantly disrupted the pre-formed fibrillar aggregates of Tau-derived PHF6 (VQIVYK) peptide and full-length tau protein in vitro, in a dose-dependent manner as evident from ThS assay, CD spectroscopy, and TEM. Molecular dynamics simulation of PHF6 oligomers and fibrils with the Naphthoquinone-Tryptophan hybrids provides a possible structure-function based mechanism-of-action, highlighting the role of hydrophobic interaction and hydrogen bond formation during fibril disassembly. These findings signify the effectiveness of NQTrp and Cl-NQTrp in disassembling fibrillar aggregates and may help in designing novel hybrid molecules for AD treatment.

Simplified method to obtain enhanced expression of tau protein from E. coli and one-step purification by direct boiling.

Tau is an intrinsically disordered protein responsible for maintaining the structure and stability of axonal microtubules. However, in certain disease conditions including Alzheimer's disease, tau protein may undergo biochemical and structural changes to form intracellular aggregates. Since tau is a proline- and arginine-rich eukaryotic protein, heterologous expression in Escherichia coli often results in poor yield and has been a major technical challenge. In the current work, we have improved the expressed yield of tau by overcoming codon bias problem and established a simplified protocol for efficient extraction. The reported method has two distinct features: (i) enhanced tau expression (upto eightfold) by supplementing deficient tRNAs that aid in rapid translation and (ii) direct boiling of expressed E. coli cells to extract tau with no separate cell lysis step. We further demonstrate that tau extracted by the direct boiling method is similar to tau purified by size-exclusion chromatography exhibiting similar structural and biophysical characteristics including aggregation propensity. Since morphologies and in vitro toxicity of fibrillar tau aggregates were also similar, tau extracted by the one-step direct boiling method can be used for tau aggregation assays without any additional purification.