Green Tea Extracts EGCG and EGC Display Distinct Mechanisms in Disrupting Aβ42 Protofibril

The amyloid beta (A beta) fibrillar aggregate is the hallmark of Alzheimer's disease (AD). Disassembling preformed fibril or inhibiting aggregation is considered as a therapeutic strategy for AD. Increasing evidence shows that green tea extracts, epigallocatechin-3-gallate (EGCG, containing an extra gallic acid ester group compared to EGC) and epigallocatechin (EGC), can disassociate A beta fibrils and attenuate A beta toxicity. However, the underlying molecular mechanism is poorly understood. Herein, we performed microsecond all-atom molecular dynamics (MD) simulations to investigate the influences of EGCG/EGC on the newly cryo-EM resolved LS-shaped A beta(42) protofibrils and their detailed interactions. MD simulations demonstrate that both EGCG and EGC can disrupt A beta(42) protofibril and EGCG displays a higher disruptive capacity than EGC. EGCG alters the L-shape of A beta(42) protofibril by breaking the hydrogen bond between H6 and E11 through pi-pi interactions with residues H14/Y10 and hydrogen-bonding interactions with El 1, while EGC remodels the L-shape by inserting into the hydrophobic core formed by A2, F4, L34, and V36 and via aromatics interaction with H6/Y10. EGCG disrupts the salt bridges between the K28 side chain and A42 COO- through hydrogen-bonding interaction with A42 and cation-pi interaction between its gallic acid ester group and K28, while EGC damages the salt bridges through hydrophobic interactions with V39 and 141 as well as with 132, M35, and V40 located in the C-terminal hydrophobic core. This study demonstrates the pivotal role of the gallic acid ester group of EGCG in disrupting A beta(42) protofibril and provides atomic-level insights into the distinct mechanism by which EGCG and EGC disrupt A beta protofibril, which could be useful for designing amyloid inhibitors.