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摘要
The human amyloid beta (A beta) peptides, A beta(1-40) and A beta(1-42), structural modifications, from soluble monomers to fully formed fibrils through intermediate structures, were investigated, and the results were compared with those obtained for the inverse A beta(40-1) and A beta(42-1), mutant A beta(1-40)Phe(10) and A beta(1-40)Nle(35), and rat A beta(1-40)Rat peptide sequences. The aggregation was followed at a slow rate, in chloride free media and room temperature, and revealed to be a sequence-structure process, dependent on the physicochemical properties of each A beta peptide isoforms, and occurring at different rates and by different pathways. The fibrilization process was investigated by atomic force microscopy (AFM), via changes in the adsorption morphology from: (i) initially random coiled structures of similar to 0.6 nm height, corresponding to the A beta peptide monomers in random coil or in alpha-helix conformations, to (ii) aggregates and proto-fibrils of 1.5-6.0 nm height and (iii) two types of fibrils, corresponding to the A beta peptide in a beta-sheet configuration. The reactivity of the carbon electrode surface was considered. The hydrophobic surface induced rapid changes of the A beta peptide conformations, and differences between the adsorbed fibrils, formed at the carbon surface (beaded, thin, <2.0 nm height) or in solution (long, smooth, thick, >2.0 nm height), were detected. Differential pulse voltammetry showed that, according to their primary structure, the A beta peptides undergo oxidation in one or two steps, the first step corresponding to the tyrosine amino acids oxidation, and the second one to the histidine and methionine amino acids oxidation. The fibrilization process was electrochemically detected via the decrease of the Ab peptide oxidation peak currents that occurred in a time dependent manner.
- 出版日期2016-7-5
