Impact of the mutation A21G (Flemish variant) on Alzheimer's beta-amyloid dimers by molecular dynamics simulations.

Soluble oligomers of the amyloid beta-protein (Abeta) are linked to Alzheimer's disease. Irrespective of the nature of the nucleus before fibril growth, dimers are essential species in Abeta assembly, but their transient character has precluded, thus far, high-resolution structure determination. We have investigated the effects of the point mutation A21G on Abeta dimers by performing high temperature all-atom molecular dynamics simulations of Abeta(40), Abeta(42), and their Flemish variants (A21G) starting from their fibrillar conformations. Abeta dimers are found in equilibrium between various topologies, and the absence of common structural features shared by the four species makes problematic the design of a unique inhibitor for blocking dimers. We also show that the impact of the point mutation A21G on Abeta structure and dynamics varies from Abeta(40) to Abeta(42). Finally, we provide a possible structural explanation for the reduced aggregation rate of Abeta fibrils containing the Flemish disease-causing mutation.