Study Of Cyclic Peptide LVFFARK On The Inhibition Of Amyloid β Protein Aggregation

Alzheimer’s disease（Alzheimer’s disease,AD）is the most common form of dementia,and amyloidβprotein’s misfolding and aggregation is an important inducement of AD.Inhibition of Aβfibrillation is thus a promising therapeutic approach to the prevention and treatment of AD.Previously,we designed a heptapeptide inhibitor,LVFFARK（LK7）,based on the fragment of Aβ_17-21 of full-length Aβprotein.LK7 shows promising inhibitory capability on Aβaggregation,but it was prone to self-assembling and the aggregates has strong cytotoxicity,which hinders its practical application.In order to improve the above defects of LK7,in this study,we modified LK7 by a head-to-tail cyclization to obtain cyclic LK7（cLK7）.The physical and chemical properties and the inhibitory effect on Aβaggregation were investigated by extensive experimental studies.The results indicate that cLK7 exhibited different self-assembly behavior from LK7,LK7 tends to form elongated dense fibrous aggregates,while cLK7 aggregated into dispersed small spherical particles,and the aggregates showed very low cytotoxicity toward SH-SY5Y and PC-12 cells.Besides,cLK7 possessed higher stability against proteolysis than LK7.Thermodynamic analysis revealed that both LK7 and cLK7 could bind to Aβ₄₀by electrostatic interactions,hydrogen bonding and hydrophobic interactions,but the binding affinity of cLK7 for Aβ₄₀（K_D=5.89μM）was eight times higher than that of LK7（K_D=48.13μM）due to its higher hydrophobic interactions.The strong binding made cLK7 could effectively bind to Aβ40 monomers and enable to stabilize the initial secondary structure of Aβ₄₀,potently inhibit its nucleation,aggregation and redirect its aggragation to an off-pathway mechanism,so it can significantly reduce the cytotoxicity induced by Aβaggregation.By contrast,LK7 could only moderately inhibit Aβ₄₀ fibrillation and cytotoxicity at low concentrations.The findings indicate that cyclization is a promising approach to alleviating the self-aggregation and enhancing the performance of their inhibitory effects on the design of peptide-based Aβaggregation inhibitors.