Insight into the internal structure of amyloid-β oligomers by isotope-edited Fourier transform infrared spectroscopy

• The internal structure of amyloid-β (Aβ) oligomers was investigated with isotope-edited Fourier transform infrared spectroscopy. Homo-oligomers of Aβ(40) and Aβ(42) were prepared from unlabeled and C-13, N-15-labeled monomeric Aβ and from mixtures of these. For the unlabeled peptides, two main bands were observed in (H2O)-H-2 at 1685 and 1622 cm(-1) for Aβ(40) and at 1685 and 1626 cm(-1) for Aβ(42). These band positions indicate that the number of strands per sheet is at least four. The obtained experimental amide I spectra were simulated using a number of structural models (antiparallel β-sheets, β-barrels and a dodecamer structure). According to experiments and calculations, the main C-13-band shifts down at increasing molar ratio of labeled peptides. This shift occurs when vibrational coupling becomes possible between C-13-amide groups in close-by strands. It is small, when intervening C-12-strands increase the distance between C-13-strands; it is large, when many neighboring strands are labeled. The shift depends on the internal structure of the peptides within the oligomers, i.e. on the building block that each peptide molecule contributes to the β-sheets of the oligomers. The shift is largest, when individual peptides contribute just a single strand surrounded by strands from other peptide molecules. It is smaller when each molecule forms two or three adjacent strands. As indicated by a comparison between experiment and computation, the number of adjacent β-strands per peptide molecule is two for Aβ(40) oligomers and two or more for Aβ(42) oligomers. Our results are well explained by regular, antiparallel β-sheets or β-barrels.

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Nyckelord

Biophysics

biofysik

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ref (ämneskategori)

art (ämneskategori)