title: Two-dimensional infrared spectra of isotopically diluted amyloid fibrils from Abeta40.
abstract: 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.
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323, USA.
authors.forename: Yung Sam
authors.initials: YS
authors.lastname: Kim
authors.forename: Liu
authors.initials: L
authors.lastname: Liu
authors.forename: Paul H
authors.initials: PH
authors.lastname: Axelsen
authors.forename: Robin M
authors.initials: RM
authors.lastname: Hochstrasser
mesh_terms: D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000737:chemistry*; D002247:Carbon Isotopes / Q000737:chemistry; D005998:Glycine / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007553:Isotope Labeling; D008969:Molecular Sequence Data; D010103:Oxygen Isotopes / Q000737:chemistry; D010446:Peptide Fragments / Q000737:chemistry*; D011487:Protein Conformation; D013055:Spectrophotometry, Infrared / Q000379:methods; D017550:Spectroscopy, Fourier Transform Infrared; D014732:Vibration
chemical_list: D016229:Amyloid beta-Peptides; D002247:Carbon Isotopes; D010103:Oxygen Isotopes; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40); D005998:Glycine