Tryptophan residues in alpha-galactosidase from Trichoderma reesei

Area of Science:

• Biochemistry
• Enzymology
• Protein Chemistry

Background:

• Alpha-galactosidase is a key enzyme involved in various biological processes.
• Understanding the enzyme's active site and conformational dynamics is crucial for its functional characterization.

Purpose of the Study:

• To investigate the location of tryptophan residues in alpha-galactosidase relative to the galactose binding site.
• To analyze the enzyme's conformational changes upon modification of active site sulfhydryl groups.
• To study the fluorescence quenching mechanisms of alpha-galactosidase.

Main Methods:

• Chemical modification of tryptophan residues using N-bromosuccinimide.
• Enzyme inhibition assays with galactose.
• Analysis of enzyme inactivation kinetics.
• Fluorescence spectroscopy to study quenching by heavy metal ions (Hg2+, Ag+).
• Determination of Forster's radii for protein-chromophore complexes.
• Investigation of dynamic fluorescence quenching.

Main Results:

• Tryptophan residues are not located in the galactose binding site, as demonstrated by modification experiments.
• Two distinct groups of tryptophan residues with different accessibility were identified.
• Specific quenching of fluorescence by Hg2+ and Ag+ ions indicates enzyme conformational changes.
• Abnormal dynamic quenching behavior was observed, necessitating a modified Stern-Volmer equation.

Conclusions:

• The study elucidates the structural and functional properties of alpha-galactosidase.
• It provides insights into the enzyme's active site and conformational flexibility.
• A modified Stern-Volmer equation is proposed for a more accurate description of dynamic quenching in this enzyme.