title: Directly Probing Intermolecular Structural Change of a Core Fragment of β2-Microglobulin Amyloid Fibrils with Low-Frequency Raman Spectroscopy.
abstract: Amyloid fibrils, which are ordered aggregates of proteins or peptides, have attracted keen interest because their deposition causes serious human diseases. Despite many studies utilizing X-ray crystallography, solid-state NMR, and other methods, intermolecular interactions governing the fibril formation remain largely unclear. Here, we used low-frequency Raman (LFR) spectroscopy to investigate the intermolecular β-sheet structure of a core fragment of β2-microglobulin amyloid fibrils, β2m21-29, in aqueous buffer solutions. The LFR spectra (approximately 10-200 cm-1) of β2m21-29amyloid fibrils measured at different pH values (ranging from 6.8 to 8.0) revealed a broad-spectral pattern with a maximum at ∼80 cm-1below pH 7.2 and at ∼110 cm-1above pH 7.4. This observation is attributed to a pH-dependent structural change from an antiparallel to a parallel intermolecular β-sheet structure. Multivariate curve resolution-alternating least-squares (MCR-ALS) analysis enabled us to decompose the apparently monotonous LFR spectra into three distinctly different contributions: intermolecular vibrations of the parallel and antiparallel β-sheets and intramolecular vibrations of the peptide backbone. Peak positions of the obtained LFR bands not only exhibit a much more pronounced difference between the two β-sheets than the conventional amide I band, but they also suggest stronger intermolecular interaction, due presumably to the hydrophobic effect, in the parallel β-sheet than in the antiparallel β-sheet. The present results show that LFR spectroscopy in combination with the MCR-ALS analysis holds promise for real-time tracking of the intermolecular dynamics of amyloid fibril formation under physiological conditions.
authors.affiliation: Department of Applied Chemistry, National Chiao Tung University , Hsinchu 30010, Taiwan.
authors.forename: Shinsuke
authors.identifier: 0000-0002-2035-2068
authors.initials: S
authors.lastname: Shigeto
authors.affiliation: Department of Applied Chemistry, National Chiao Tung University , Hsinchu 30010, Taiwan.
authors.forename: Chun-Fu
authors.initials: CF
authors.lastname: Chang
authors.affiliation: Graduate School of Pharmaceutical Sciences, Tohoku University , Sendai 980-8578, Japan.
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Hiramatsu
mesh_terms: D000682:Amyloid / Q000737:chemistry*; D006801:Humans; D016018:Least-Squares Analysis; D015999:Multivariate Analysis; D011487:Protein Conformation; D013059:Spectrum Analysis, Raman; D001613:beta 2-Microglobulin / Q000737:chemistry*
chemical_list: D000682:Amyloid; D001613:beta 2-Microglobulin