Free Energy Landscape for Alpha-Helix to Beta-Sheet Interconversion in Small Amyloid Forming Peptide under Nanoconfinement.

Understanding the mechanism of fibrillization of amyloid forming peptides could be useful for the development of therapeutics for Alzheimer's disease (AD). Taking this standpoint, we have explored in this work the free energy profile for the interconversion of monomeric and dimeric forms of amyloid forming peptides into different secondary structures namely beta-sheet, helix, and random coil in aqueous solution using umbrella sampling simulations and density functional theory calculations. We show that the helical structures of amyloid peptides can form β sheet rich aggregates through random coil conformations in aqueous condition. Recent experiments ( Chem. Eur. J. 2018, 24, 3397-3402 and ACS Appl. Mater. Interfaces 2017, 9, 21116-21123) show that molybdenum disulfide nanosurface and nanoparticles can reduce the fibrillization process of amyloid beta peptides. We have unravelled the free energy profile for the interconversion of helical forms of amyloid forming peptides into beta-sheet and random coil in the presence of a two-dimensional nanosurface of MoS2. Results indicate that the monomer and dimeric forms of the peptides adopt the random coil conformation in the presence of MoS2 while the helical form is preferable for the monomeric form and that the beta-sheet and helix forms are the preferable forms for dimers in aqueous solution. This is due to strong interaction with MoS2 and intramolecular hydrogen bonds of random coil conformation. The stabilization of random coil conformation does not lead to a β sheet like secondary structure for the aggregate. Thus, the confinement of MoS2 promotes deaggregation of amyloid beta peptides rather than aggregation, something that could be useful for the development of therapeutics for AD.