Effect of Alzheimer's Disease Causative and Protective Mutations on the Hydration Environment of Amyloid-beta

This study investigates the local structure and dynamics of hydration water around the intrinsically disordered protein amyloid-beta (A beta) and its Alzheimer's disease causative N-terminus mutants, i.e., A2V, Taiwan (D7H), Tottori (D7N), and English (H6R), and the protective A2T mutant via atomistic MD simulations. The effect of mutations on the hydration environment around different domains of this protein is evaluated through the surface distribution function, tetrahedral order parameter, and the survival probability of the water molecules within the hydration shell. The water density around the hydrophobic hp1 (17-21) domain is found to be higher for the A2T mutant as compared to the wild-type A beta and its selected causative mutants. The average tetrahedral order parameter of water molecules around the hydrophobic hp1 (17-21) domain shows that water molecules are less ordered around the A2V, Taiwan, Tottori, and English mutants and more ordered around the A2T mutant than those of the wild-type protein. The survival probability decays rapidly for the A2V, Taiwan, Tottori, and English mutants, while it is comparatively slower for the protective A2T mutant. These results exhibit different hydration environments for the causative and protective mutants highlighting the differential roles of charge and hydrophobicity.