Destabilizing Alzheimer's Aβ42 Protofibrils with Morin: Mechanistic Insights from Molecular Dynamics Simulations

Alzheimer's disease is a progressive, neurodegenerative disorder that is the leading cause of senile dementia, afflicting millions of individuals worldwide. Since the identification of the amyloid beta-peptide (A beta) as the principal toxic entity in the progression of Alzheimer's disease, numerous attempts have been made to reduce endogenous A beta production and deposition, including designing inhibitors of the proteases that generate the peptide, generating antibodies against A beta aggregates, utilizing metal chelators, and identifying small molecules that target the peptide during the aggregation pathway. The last approach is particularly attractive, as A beta is normally present in vivo, but aggregation is a purely pathological event. Studies conducted in vitro and in vivo have suggested that administration of flavonoids, compounds naturally present in many foods, including wine and tea, can prevent and reverse A beta aggregation, but mechanistic details are lacking. In this work, we employ atomistic, explicit-solvent molecular dynamics (MD) simulations to identify the mechanism of A beta fibril destabilization by morin, one of the most effective anti-aggregation flavonoids, using a model of the mature A beta fibril. Through the course of 24 simulations totaling 4.3 mu s, we find that morin can bind to the ends of the fibrils to block the attachment of an incoming peptide and can penetrate into the hydrophobic core to disrupt the Asp23-Lys28 salt bridges and interfere with backbone hydrogen bonding. The combination of hydrophobicity, aromaticity, and hydrogen bonding capacity of morin imparts the observed behavior.