Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 105, Issue 22, Pages 7720-7725Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0802993105
Keywords
beta-amyloid 40; exciton; two-dimensional infrared spectroscopy
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Funding
- NCRR NIH HHS [P01RR01348, P41 RR001348] Funding Source: Medline
- NIGMS NIH HHS [GM76201, R37 GM012592, GM12592, R01 GM076201, GM 48310, R01 GM012592] Funding Source: Medline
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The 2D IR spectra of the amide-I vibrations of amyloid fibrils from A beta 40 were obtained. The matured fibrils formed from strands having isotopic substitution by C-13 = O-18 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.
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