Two-dimensional infrared spectra of isotopically diluted amyloid fibrils from Abeta40

Proc Natl Acad Sci U S A. 2008 Jun 3;105(22):7720-5. doi: 10.1073/pnas.0802993105. Epub 2008 May 22.


The 2D IR spectra of the amide-I vibrations of amyloid fibrils from Abeta40 were obtained. The matured fibrils formed from strands having isotopic substitution by (13)C (18)O at Gly-38, Gly-33, Gly-29, or Ala-21 show vibrational exciton spectra having reduced dimensionality. Indeed, linear chain excitons of amide units are seen, for which the interamide vibrational coupling is measured in fibrils grown from 50% and 5% mixtures of labeled and unlabeled strands. The data prove that the 1D excitons are formed from parallel in-register sheets. The coupling constants show that for each of the indicated residues the amide carbonyls in the chains are separated by 0.5 +/- 0.05 nm. The isotope replacement of Gly-25 does not reveal linear excitons, consistent with the region of the strand having a different structure distribution. The vibrational frequencies of the amide-I modes, freed from effects of amide vibrational excitation exchange by 5% dilution experiments, point to there being a component of an electric field along the fibril axis that increases through the sequence Gly-38, Gly-33, Gly-29. The field is dominated by side chains of neighboring residues.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amyloid beta-Peptides / chemistry*
  • Carbon Isotopes / chemistry
  • Glycine / chemistry
  • Humans
  • Hydrogen-Ion Concentration
  • Isotope Labeling
  • Molecular Sequence Data
  • Oxygen Isotopes / chemistry
  • Peptide Fragments / chemistry*
  • Protein Conformation
  • Spectrophotometry, Infrared / methods
  • Spectroscopy, Fourier Transform Infrared
  • Vibration


  • Amyloid beta-Peptides
  • Carbon Isotopes
  • Oxygen Isotopes
  • Peptide Fragments
  • amyloid beta-protein (1-40)
  • Glycine