The circular dichroism of lysozyme

Area of Science:

• Biochemistry
• Spectroscopy
• Protein Structure

Background:

• Circular dichroism (CD) spectroscopy is a powerful tool for analyzing protein secondary and tertiary structures.
• Lysozyme and alpha-lactalbumin are well-studied model proteins with known structures and functions.

Purpose of the Study:

• To investigate the contribution of specific tryptophan residues (Trp-62 and Trp-108) to the circular dichroism spectra of hen egg white lysozyme.
• To re-evaluate the interpretation of CD spectra for lysozymes and alpha-lactalbumins based on these findings.

Main Methods:

• Circular dichroism spectroscopy was employed to measure spectra of native lysozyme and its selectively oxidized derivatives.
• Measurements were conducted across a pH range and wavelength spectrum (200-310 nm).
• The effect of saccharide binding on the CD spectra was also assessed.

Main Results:

• The positive rotational strength in the 280-300 nm region of the CD spectra is not primarily attributed to Trp-62 or Trp-108.
• The CD spectral region from 200-230 nm remained largely unchanged between native lysozyme and its derivatives.
• Saccharide binding had minimal impact on the 200-230 nm spectral region.

Conclusions:

• The study provides new insights into the assignment of spectral features in lysozyme CD spectra.
• The findings necessitate a reinterpretation of CD spectra for lysozymes and alpha-lactalbumins, particularly concerning tryptophan residue contributions.
• Specific tryptophan residues may not be the sole determinants of observed spectral characteristics.