Paschou, A.M.; Christofilos, D.; Arvanitidis, J.; Pavlidou, E.; Zizak, I.; Katsikini, M.: Hydrostatic pressure response of alpha-keratin investigated with Raman spectroscopy. International Journal of Biological Macromolecules 328 (2025), p. 147401/1-10
10.1016/j.ijbiomac.2025.147401
Open Accesn Version
Abstract:
Keratins represent an important class of sulfur-rich structural proteins. In this study, the pressure response of alpha-keratin, extracted from sheep wool, was investigated using Raman spectroscopy up to 4 GPa. A non-polar liquid (a Fluorinert (TM) FC70/77 mixture) served as the Pressure Transmitting Medium (PTM) in a Diamond Anvil Cell (DAC). Scanning Electron Microscopy (SEM) and Small-Angle X-ray Scattering (SAXS) were used for the morphological and structural characterization of the sample. Three Raman bands were monitored during compression and decompression: (CH)-H-deformation, amide-I (dominated by the C=O stretching vibration of the peptide bond) and (CH)-H- stretching vibrations centered at approximately 1450, 1670 and 2940 cm(-1), respectively. The deformation modes of the (CH)-H- bonds exhibited a weak positive pressure dependence (similar to 1.7 cm(-1)/GPa), whereas the corresponding stretching modes showed a much stronger dependence (6-9 cm(-1)/GPa). A positive slope (similar to 2.2 cm(-1)/GPa) was also observed for the amide-I band, consistent with CO strengthening in the peptide bonds under compressin. This behavior contrasts with that of collagen, which exhibits a negative pressure slope for the same vibrational mode. The opposite responses are discussed in relation to the different structural roles of hydrogen bonding in these two fibrous proteins. Overall, the response of keratin to high hydrostatic pressure is reversible.