Thermodynamic analysis of the molecular interactions between amyloid beta-peptide 42 and (-)-epigallocatechin-3-gallate.

One of the key factors of Alzheimer's disease (AD) is the conversion of amyloid beta-peptide (Abeta) from its soluble random coil form into various aggregated forms. (-)-Epigallocatechin-3-gallate (EGCG) has been proved effective in preventing the aggregation of Abeta, but the thermodynamic mechanisms are still unclear. In this work, isothermal titration calorimetry (ITC) was utilized to study the interactions between Abeta42 and EGCG at different temperatures, salt concentrations, pH values, and EGCG and Abeta42 concentrations. Molecular dynamics (MD) simulations were performed to study the hydrogen bonding between Abeta42 and EGCG. The results indicate that the binding stoichiometry N is linearly related to the EGCG/Abeta42 ratio. Hydrophobic interaction and hydrogen bonding are both substantial in the binding process, but the extent of their contributions changes with experimental conditions. Namely, the predominant interaction gradually shifts from a hydrogen bonding to a hydrophobic interaction with the increase of the EGCG/Abeta42 ratio, resulting in a transition of the binding from enthalpy-driven to entropy-driven. This experimental observation is validated by the MD simulations. The binding of EGCG to Abeta42 can be promoted by increasing temperature and salt concentration and changing pH away from Abeta42's pI. The findings have provided new insight into the molecular interactions between Abeta42 and EGCG from a thermodynamic perspective and are expected to facilitate the research on the inhibition of Abeta42 aggregation.