α,β-Dehydroamino-Acid-Containing Peptides Resist Proteolysis and Inhibit Aggregation of a Tau-Derived Model Peptide

Analogues of a tau protein subunit (VQIVYK, or PHF6) containing a medium-sized or bulky α,β-dehydroamino acid (ΔAA) were synthesized and evaluated for their ability to inhibit aggregation of the parent peptide. The ΔAAs were constructed via the dehydration of the corresponding β-hydroxyamino acids. Some analogues were assembled by solid-phase peptide synthesis, but a solution-phase strategy was required in two cases due to the failure of a key azlactone ring-opening amidation. The ΔAA-containing peptides are 2-20 times more stable to proteolysis than related proline-containing PHF6 analogues. Transmission electron microscopy and Thioflavin T (ThT) assays revealed that the ΔAA-containing analogues are potent inhibitors of PHF6 aggregation. The impact of the analogues on the morphology of the preformed PHF6 fibrils was also investigated. This study validates the use of medium-sized or bulky ΔAAs as tools for increasing the proteolytic stability of functional peptides.