Amyloid Beta Peptide VHHQ, KLVFF, and IIGLMVGGVV Domains Involved in Fibrilization: AFM and Electrochemical Characterization

The time-dependent structural modifications and oxidation behavior of specifically chosen five short amyloid beta (A beta) peptides, A beta(1-16), A beta(1-28), A beta(10-20), A beta(12-28), and A beta(17-42), fragments of the complete human A beta(1-40) peptide, were investigated by atomic force microscopy (AFM) and voltammetry. The objective was to determine the influence of different A beta domains (VHHQ that contains electroactive histidine H residues, KLVFF that is the peptide hydrophobic aggregation core, and IIGLMVGGVV that is the C-terminus hydrophobic region), and of A beta peptide hydrophobicity, in the fibrilization mechanism. The short A beta peptides absence of aggregation or the time-dependent aggregation mechanisms, at room temperature, in free chloride media, within the time window from 0 to 48 h, were established by AFM via changes in their adsorption morphology, and by differential pulse voltammetry, via modifications of the amino acid residues oxidation peak currents. The first oxidation peak was of tyrosine Y residue and the second peak was of histidine H and methionine M residues oxidation. A correlation between the presence of an intact highly hydrophobic KLVFF aggregation core and the time-dependent changes on the A beta peptides aggregation was found. The hydrophobic C-terminal domain IIGLMVGGVV, present in the A beta(1-40) peptide, also contributed to accelerate the formation of A beta(1-40) peptide aggregates and fibrils.