Optical properties of lysozyme. pH and saccharide binding difference spectra

Area of Science:

• Biochemistry
• Spectroscopy
• Protein Chemistry

Background:

• Lysozymes are enzymes with critical roles in biological systems.
• Understanding lysozyme's structural and functional dynamics is key to its applications.
• Spectroscopic methods provide sensitive probes for molecular interactions.

Purpose of the Study:

• To investigate the spectral differences in hen egg white (HEW) and turkey egg white (TEW) lysozymes.
• To analyze the effects of pH changes and saccharide binding on lysozyme spectra.
• To elucidate the impact of specific tryptophan residue oxidation on lysozyme's spectral characteristics.

Main Methods:

• UV-Vis difference spectroscopy was employed.
• pH-dependent spectral changes were recorded.
• Saccharide binding effects on spectra were measured.
• Site-specific oxidation of tryptophan residues (Trp-62, Trp-108) was performed.

Main Results:

• Identical pH difference spectra were observed for HEW, TEW, and Oxa-62 lysozymes.
• Oxidation of Trp-108 significantly altered both high and low pH difference spectra.
• Saccharide binding enhanced low pH difference spectra for HEW and Oxa-62 lysozymes.
• Oxidation of Trp-62 or Trp-108 modified the spectral signatures of saccharide binding.

Conclusions:

• The study provides insights into the perturbations causing lysozyme difference spectra.
• Glu-35 and other tryptophan residues are implicated in pH-dependent spectral changes.
• Trp-108 plays a major role in the spectral response to saccharide binding.
• Oxidation of Trp-108 leads to absorbance changes in the 250-265 nm region upon saccharide binding or Glu-35 ionization.