Amyloid beta(1-42) in aqueous environments: Effects of ionic strength and E22Q (Dutch) mutation

Development of extracellular plaques characteristic of Alzheimer's disease is related to aggregation of amyloid peptides. The A beta-42 peptide is the most aggregation prone species, and some missense mutant forms increase this aggregation ability. Due to its poor solubility as monomer in aqueous solutions, A beta-42 conformational transitions in water have been largely investigated by molecular dynamics. Here we report an all-atom molecular dynamics analysis of the A beta-42 peptide in aqueous environment using as starting conformation a structure obtained in an isotropic, low-polarity medium, representing a plausible model for the membrane-bound species. While previous studies commonly show that A beta-42 is largely unstructured in aqueous solution, here we report that this peptide can adopt partially folded structures. Importance of ionic strength has been also investigated, showing that at physiological ionic strength condition a loop stabilizing electrostatic interaction involving Lys28 builds up. In addition, besides stable alpha-helix structures, we observe the appearance of 3(10) helix, similar to what was reported experimentally for the A beta-40 species. The effect of E22Q (Dutch) mutation in high ionic strength condition has been explored. We show that this mutation has a dramatic impact on the A beta-42 structure. Instead of a partially folded, but extended, conformation obtained with the wild type, the E22Q assumes a two-helix collapsed one due to the clustering of hydrophobic residues. (C) 2013 Elsevier B.V. All rights reserved.