Unravelling the role of amino acid sequence order in the assembly and function of the amyloid-β core

Abstract

The amino acid sequence plays an essential role in amyloid formation. Here, using the central core recognition module of the Aβ peptide and its reverse sequence, we show that although both peptides assemble into β-sheets, their morphologies, kinetics and cell toxicities display marked differences. In addition, the native peptide, but not the reverse one, shows notable affinity towards bilayer lipid model membranes that modulates the aggregation pathways to stabilize the oligomeric intermediate states and function as the toxic agent responsible for neuronal dysfunction.

Fig. 1. (a) TEM and (b and c) AFM images of Aβ(16-22). (d) TEM and (e and f) AFM images of Aβ(22-16). (g and h) CD spectra for Aβ(16-22) (g) and Aβ(22-16) (h). (i and j) FTIR spectra for the native peptide (i) and its reverse sequence (j).

Fig. 2. (a and b) Kinetics of fiber formation as observed by TEM for Aβ(16-22) (a) and Aβ(22-16) (b). (c and d) CD spectra showing the transition from unstructured conformation into β-sheet over time for Aβ(16-22) (c) and Aβ(22-16) (d).

Fig. 3

(a) ζ-potential of the two peptides. (b) MTT cell viability assay. (c–f) Cryo-TEM of Aβ(16-22) (c and d) and Aβ(22-16) (e and f) in the presence of lipid vesicles. Insets show negatively stained images of the peptides only. (g) Kinetics of peptide fibrillation using ThT fluorescence. (h) CD spectroscopy secondary structure analysis of Aβ(16-22) and Aβ(22-16) with and without lipid vesicles. In (g and h): blue and red spectra represent Aβ(16-22) and Aβ(22-16), respectively. Broken line represents peptide only and continuous line represents peptide with lipid vesicles. Scale bar for (c–f) is 200 nm.