Controlling Amyloid Beta Peptide Aggregation and Toxicity by Protease-Stable Ligands

Polymerization of soluble amyloid beta (A beta) peptide into protease-stable insoluble fibrillary aggregates is a critical step in the pathogenesis of Alzheimer's disease (AD). The N-terminal (NT) hydrophobic central domain fragment 16KLVFF20 plays an important role in the formation and stabilization of beta-sheets by self-recognition of the parent A beta peptide, followed by aggregation of A beta in the AD brain. Here, we analyze the effect of the NT region inducing beta-sheet formation in the A beta peptide by a single amino acid mutation in the native A beta peptide fragment. We designed 14 hydrophobic peptides (NT-01 to NT-14) by a single mutation at 18Val by using hydrophobic residues leucine and proline in the natural A beta peptide fragment (KLVFFAE) and analyzed its effect on the formation of A beta aggregates. Among all these peptides, NT-02, NT-03, and NT-13 significantly affected the A beta aggregate formation. When the NT peptides were coincubated with the A beta peptide, a significant reduction in beta-sheet formation and increment in random coil content of A beta was seen, confirmed by circular dichroism spectroscopy and Fourier transform infrared spectroscopy, followed by the reduction of fibril formation measured by the thioflavin-T (ThT) binding assay. The aggregation inhibition was monitored by Congo red and ThT staining and electron microscopic examination. Moreover, the NT peptides protect the PC-12 differentiated neurons from A beta-induced toxicity and apoptosis in vitro. Thus, manipulation of the A beta secondary structure with protease-stable ligands that promote the random coil conformation may provide a tool to control the A beta aggregates observed in AD patients.