Secondary conformations and temperature effect on structural transformation of amyloid β (1-28), (1-40) and (1-42) peptides

Secondary structure of three amyloid beta-peptides [AP(1-28), Abeta(1-40) and Abeta(1-42)] in the solid state was respectively determined by Fourier transform infrared (FT-IR) microspectroscopy. Their thermal-dependent structural transformation were also investigated by FTIR microspectroscopy equipped with a thermal analyzer. The present result demonstrates that the solid-state Abeta(1-28), Abeta(1-40) and Abeta(1-42) peptides showed a significant IR spectral difference in the amide I and II bands. The secondary conformation of Abeta(1-28) peptide was the combination of major beta-sheet and minor alpha-helix with little random coil structures, but Abeta(1-40) peptide showed the co-existence of major beta-sheet and minor random coil with little alpha-helix structures. Abeta(1-42) peptide mainly consisted of the predominant beta-sheet structure. Although the intact Abeta(1-28), Abeta(1-40) or Abeta(1-42) peptide exhibits a different secondary structure, a similar beta-conformation may form after thermal treatment. A thermal-dependent transition was found for solid Abeta(1-28) and Abeta(1-40) peptides near 40degreesC and 45degreesC, respectively. There was no transition temperature for solid Abeta(1-42) peptide, however, due to only a very little level of alpha-helix and random coil structure containing in the solid Abeta(1-42) peptide. The thermal denaturation plays an important role in the structural transformation from alpha-helix/random coil to beta-sheet.