Structural Discrimination between Aβ(1-40) and Aβ(1-42) Peptides in Films with Vibrational Circular Dichroism Spectroscopy.

Abstract

The secondary structure of full-length Aβ(1-40) and Aβ(1-42) peptides in films has been investigated with IR and vibrational circular dichroism (VCD) spectroscopy. From IR spectra, it is shown that the prepared films of Aβ(1-40) and Aβ(1-42) mainly comprise the β-sheet conformation that is characteristic of aggregated and fibrous Aβ. In the VCD spectra, the Aβ(1-42) film shows an intense and sharp band with left-handed optical activity at around 1625 cm-1, while the Aβ(1-40) film shows a weak and broad band with right-handed activity at around 1630 cm-1. The wavenumbers are characteristic of the β-sheet conformation. It has been clarified that the aggregated Aβ(1-42) adopts the β-sheet conformation with reverse optical activity compared with the aggregated Aβ(1-40). The left-handed optically active β-sheet of the aggregated Aβ(1-42) may contribute to the formation of protofibrils, which are a cause for the higher neurotoxicity of Aβ(1-42) fibrils than Aβ(1-40) fibrils.