Head-to-tail cyclization of a heptapeptide eliminates its cytotoxicity and significantly increases its inhibition effect on amyloid β-protein fibrillation and cytotoxicity

Abstract

Amyloid-β (Aβ) protein aggregation is the main hallmark of Alzheimer’s disease (AD). Inhibition of Aβ fibrillation is thus a promising therapeutic approach to the prevention and treatment of AD. Recently, we designed a heptapeptide inhibitor, LVFFARK (LK7). LK7 shows a promising inhibitory capability on Aβ fibrillation, but is prone to self-assembling and displays high cytotoxicity, which would hinder its practical application. Herein, we modified LK7 by a head-to-tail cyclization and obtained a cyclic LK7 (cLK7). cLK7 exhibits a different self-assembly behavior from LK7, and has higher stability against proteolysis than LK7 and little cytotoxicity to SH-SY5Y cells. Thermodynamic analysis revealed that both LK7 and cLK7 could bind to Aβ₄₀ by electrostatic interactions, hydrogen bonding and hydrophobic interactions, but the binding affinity of cLK7 for Aβ₄₀ (K_D = 4.96 µmol/L) is six times higher than that of LK7 (K_D = 32.2 µmol/L). The strong binding enables cLK7 to stabilize the secondary structure of Aβ₄₀ and potently inhibit its nucleation, fibrillation and cytotoxicity at extensive concentration range, whereas LK7 could only moderately inhibit Aβ₄₀ fibrillation and cytotoxicity at low concentrations. The findings indicate that the peptide cyclization is a promising approach to enhance the performance of peptide-based amyloid inhibitors.

Graphical abstract

Keywords

Alzheimer’s disease / amyloid β-protein / cyclic peptide / inhibition / protein aggregation

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Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature