Mid-infrared free-electron laser tuned to the amide I band for converting insoluble amyloid-like protein fibrils into the soluble monomeric form

Abstract

A mid-infrared free-electron laser (FEL) is operated as a pulsed and linearly polarized laser with tunable wavelengths within infrared region. Although the FEL can ablate soft tissues with minimum collateral damage in surgery, the potential of FEL for dissecting protein aggregates is not fully understood. Protein aggregates such as amyloid fibrils are in some cases involved in serious diseases. In our previous study, we showed that amyloid-like lysozyme fibrils could be disaggregated into the native form with FEL irradiation specifically tuned to the amide I band (1,620 cm−1). Here, we show further evidence for the FEL-mediated disaggregation of amyloid-like fibrils using insulin fibrils. Insulin fibrils were prepared in acidic solution and irradiated by the FEL, which was tuned to either 1,620 or 2,000 cm−1 prior to the experiment. The Fourier transform infrared spectroscopy (FT-IR) spectrum after irradiation with the FEL at 1,620 cm−1 indicated that the broad peak (1,630–1,660 cm−1) became almost a single peak (1,652 cm−1), and the β-sheet content was reduced to 25 from 40 % in the fibrils, while that following the irradiation at 2,000 cm−1 remained at 38 %. The Congo Red assay as well as transmission electron microscopy observation confirmed that the number of fibrils was reduced by FEL irradiation at the amide I band. Size-exclusion chromatography analysis indicated that the disaggregated form of fibrils was the monomeric form. These results confirm that FEL irradiation at the amide I band can dissect amyloid-like protein fibrils into the monomeric form in vitro.

Picosecond pulsed infrared laser tuned to amide I band dissociates polyglutamine fibrils in cells

“…The structure and function of the FEL was described in detail in previous studies [5][6][7][8][9]. The energy value used for the current experiment was in the range of 8.0-9.0 mJ, and the full-width at half maximum of the FEL waveform is 0.1-0.2 μm.…”

“…We recently discovered that a high-peak powered FEL, which has oscillation wavelengths at amide I band (C = O stretch vibration mode, 6.0-6.2 μm), can dissociate the aggregate forms of various proteins such as insulin, lysozyme, calcitonin fragment, and keratin to their monomer structures [5][6][7][8][9]. The FEL is operated as a picosecond pulsed laser with perfect linear polarization, in which one micro-pulse of 2 ps width is separated at 350 picosecond interval and one macro-pulse of 2-μs duration is structured by about 6000 of micro-pulses.…”

Infrared light as a potential therapeutic approach for neurodegeneration

“…Tiny strings of insulin fibrils prepared in an acidic solution (20% acetic acid) decreased substantially after irradiation at 6.17 µm (1620 cm -1 ), which corresponds to the amide I band. After 1 hour of irradiation, theβ-sheet content was decreased from 40% to 25%, indicating that β-sheet rich structure was reduced by FEL irradiation at the amide I band [13]. Almost same wavelength was also effective to dissociate non-amyloid keratin aggregate [30].…”

“…The mid-infrared FEL facility at the Tokyo University of Science can generate a laser beam using synchrotron radiation as a seed, with a variable wavelength within the mid-infrared region of 5-16 μm (625-2,000 cm −1 ) [13]. We introduce dissociation of polyglutamine aggregate as an example demonstrating potential usefulness of mid-infrared wavelength by FEL below.…”

“…The initial idea was brought by an observation that multiple protein aggregates can absorb most photon energy at the amide I band. Indeed, the structures of aggregated proteins was changed by a FEL tuned to the amide bands [13,[27][28][29][30].…”