Is the Viscoelasticity of Alzheimer’s Aβ42 Peptide Oligomers a General Property of Protein Oligomers Related to Their Toxicity?

The largest group of protein misfolding diseases is associated with the conversion of specific peptides or proteins from their soluble functional states into highly organized fibrillar aggregates named amyloid fibrils or plaques. The amyloid-β peptide (Aβ) is involved in pathogenesis of Alzheimer's disease (AD), being the main constituent of the amyloid plaques found in AD brains. Aβ is a proteolytic product of a transmembrane protein and due to its amphipathicity it may be retained in the membrane, and this has been shown to be crucial for neurotoxicity. Hydrophobic and electrostatic interactions strongly influence its conformation and aggregation both in solution and at interfaces. Appropriate solid sorbent surfaces were used to study the different interactions independently. Quartz crystal microbalance with dissipation monitoring (QCM-D), atomic force microscopy (AFM) and attenuated total reflection infrared spectroscopy (ATR-IR) were employed for the investigation of the behavior of Aβ peptides on planar surfaces. Aβ peptides have high affinity for hydrophobic and rough surfaces that promote aggregation. QCM-D measurements indicate that the oligomers are soft when compared to monomers, and this property might be related to the bioactivity of protein oligomers in general.