Inhibitive and Destructive Mechanisms of Chronic Traumatic Encephalopathy-Related R3-R4 Tau Peptide Chains and Protofibril by Epigallocatechin Gallate: Evidence from Molecular Dynamics Simulation

Chronic traumatic encephalopathy (CTE), a unique tauopathy, is pathologically associated with the aggregation of hyperphosphorylated tau protein into fibrillar aggregates. Inhibiting tau aggregation and disaggregating tau protofibril might be promising strategies to prevent or delay the development of CTE. Newly resolved tau fibril structures from deceased CTE patients' brains show that the R3-R4 fragment of tau forms the core of the fibrils and the structures are distinct from other tauopathies. An in vitro experiment finds that epigallocatechin gallate (EGCG) can effectively inhibit human full-length tau aggregation and disaggregate preformed fibrils. However, its inhibitive and destructive effects on the CTE-related R3-R4 tau and the underlying molecular mechanisms remain elusive. In this study, we performed extensive all-atom molecular dynamics simulations on the CTE-related R3-R4 tau dimer/protofibril with and without EGCG. The results reveal that EGCG could reduce the β-sheet structure content of the dimer, induce the dimer to form loosely packed conformations, and impede the interchain interactions, thus inhibiting the further aggregation of the two peptide chains. Besides, EGCG could reduce the structural stability, decrease the β-sheet structure content, reduce the structural compactness, and weaken local residue-residue contacts of the protofibril, hence making the protofibril disaggregated. We also identified the dominant binding sites and pivotal interactions. EGCG preferentially binds with hydrophobic, aromatic, and positively/negatively charged residues of the dimer, while it tends to bind with polar, hydrophobic, aromatic, and positively charged residues of the protofibril. Hydrophobic, hydrogen-bonding, π-π stacking, and cation-π interactions synergistically drive the binding of EGCG on both the dimer and the protofibril, but anion-π interaction only exists in the interaction of EGCG with the dimer. Our work unravels EGCG's inhibitive and destructive effects on the CTE-related R3-R4 tau dimer/protofibril and the underlying molecular mechanisms, which provides useful implications for the design of drugs to prevent or delay the progression of CTE.