Raman Microspectroscopy of Hair: Low-Frequency Markers of Protein Secondary Structure

Area of Science:

• Biophysics
• Spectroscopy
• Materials Science

Background:

• Protein secondary structure analysis is crucial for understanding protein function.
• Raman spectroscopy offers a non-destructive method for molecular vibration analysis.
• Keratin, a fibrous protein, possesses complex secondary structures.

Purpose of the Study:

• To determine specific low-frequency Raman spectral intervals indicative of protein secondary structures.
• To assign observed Raman bands to distinct structural elements within keratin.
• To establish the utility of Raman spectroscopy for studying protein secondary structures.

Main Methods:

• Raman spectroscopy was employed to analyze unpigmented human hair keratin.
• Measurements were conducted using two excitation radiation configurations: coaxial and perpendicular to the hair.
• Polarization sensitivity analysis was used to interpret spectral data.

Main Results:

• Specific Raman bands at 150 cm⁻¹ and 221 cm⁻¹ were assigned to alpha-helical structures based on polarization sensitivity.
• Vibrations associated with beta-sheet structures were identified within the 270–340 cm⁻¹ spectral range.
• Distinct spectral features correlated with varying contents of secondary structure elements in keratin.

Conclusions:

• Low-frequency Raman spectroscopy effectively probes protein secondary structures.
• The identified spectral markers provide a basis for studying alpha-helical and beta-sheet conformations in keratin.
• These findings are applicable to the broader study of protein secondary structures using Raman spectroscopy.