Two-dimensional infrared spectra of isotopically diluted amyloid fibrils from A beta 40
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- Two-dimensional infrared spectra of isotopically diluted amyloid fibrils from A beta 40
- Kim, Yung Sam; Liu, Liu; Axelsen, Paul H.; Hochstrasser, Robin M.
- β-amyloid 40; Exciton; Two-dimensional infrared spectroscopy
- Issue Date
- NATL ACAD SCIENCES
- PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OFAMERICA, v.105, no.22, pp.7720 - 7725
- The 2D IR spectra of the amide-I vibrations of amyloid fibrils from Aβ40 were obtained. The matured fibrils formed from strands having isotopic substitution by 13C=18O 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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