The role of phenolic OH groups of flavonoid compounds with H-bond formation ability to suppress amyloid mature fibrils by destabilizing ?-sheet conformation of monomeric A?17-42.

Abstract

Alzheimer's disease (AD) is a kind of brain disease that arises due to the aggregation and fibrillation of amyloid ?-peptides (A?). The peptide A?17-42 forms U-shape protofilaments of amyloid mature fibrils by cross-? strands, detected in brain cells of individuals with AD. Targeting the structure of A?17-42 and destabilizing its ?-strands by natural compounds could be effective in the treatment of AD patients. Therefore, the interaction features of monomeric U-shape A?17-42 with natural flavonoids including myricetin, morin and flavone at different mole ratios were comprehensively studied to recognize the mechanism of A? monomer instability using molecular dynamics (MD) simulations. We found that all flavonoids have tendency to interact and destabilize A? peptide structure with mole ratio-dependent effects. The interaction free energies of myricetin (with 6 OHs) and morin (with 5 OHs) were more negative compared to flavone, although the total binding energies of all flavonoids are favorable and negative. Myricetin, morin and flavone penetrated into the core of the A?17-42 and formed self-clusters of A?17-42-flavonoid complexes. Analysis of A?17-42-flavonoids interactions identified that the hydrophobic interactions related to SASA-dependent energy are weak in all complexes. However, the intermolecular H-bonds are a main binding factor for shifting U-shape rod-like state of A?17-42 to globular-like disordered state. Myricetin and morin polyphenols form H-bonds with both peptide's carbonyl and amine groups whereas flavone makes H-bonds only with amine substitution. As a result, polyphenols are more efficient in destabilizing ?-sheet structures of peptide. Accordingly, the natural polyphenolic flavonoids are useful in forming stable A?17-42-flavonoid clusters to inhibit A?17-42 aggregation and these compounds could be an effective candidate for therapeutically targeting U-shape protofilaments' monomer in amyloid mature fibrils.