Weaker N-Terminal Interactions for the Protective over the Causative Aβ Peptide Dimer Mutants.

Knowing that abeta amyloid peptide (Aβ) dimers are the smallest and most abundant neurotoxic oligomers for Alzheimer's disease (AD), we used molecular simulations with advanced sampling methods (replica-exchange) to characterize and compare interactions between the N-termini (residues 1-16) of wild type (WT-WT) and five mutant dimers under constrained and unconstrained conditions. The number of contacts and distances between the N-termini, and contact maps of their conformational landscape illustrate substantial differences for a single residue change. The N-terminal contacts are significantly diminished for the dimers containing the monomers that protect against (WT-A2T) as compared with those that predispose toward (A2V-A2V) AD and for the control WT-WT dimers. The reduced number of N-terminal contacts not only occurs at or near the second residue mutations but also is distributed through to the 10th residue. These findings provide added support to the accumulating evidence for the "N-terminal hypothesis of AD" and offer an alternate mechanism for the cause of protection from the A2T mutant.