Studies on the function of tryptophan-108 on lysozyme

Area of Science:

• Biochemistry
• Enzymology
• Protein Chemistry

Background:

• Selective chemical modification of tryptophan residues in enzymes is crucial for understanding their structure-function relationships.
• Previous studies on lysozyme's Trp-108 modification yielded ambiguous results regarding its impact on catalytic activity.

Purpose of the Study:

• To elucidate the role of Trp-108 in lysozyme's catalytic activity by resolving discrepancies from prior modification studies.
• To investigate the effects of specific Trp-108 modification on lysozyme's microenvironment and catalytic efficiency.

Main Methods:

• Selective modification of lysozyme at Trp-108 using 2-nitro-4-carboxyphenylsulfenyl chloride (NCPS-Cl).
• Isolation and purification of the modified lysozyme derivative via chromatographic fractionation.
• Sequence analysis to confirm site-specific modification.
• Physico-chemical and kinetic studies to assess residual lytic activity and analyze changes in the active site microenvironment.

Main Results:

• A lysozyme derivative modified exclusively at Trp-108 was successfully isolated.
• The modified lysozyme retained approximately 10% of its original lytic activity.
• Physico-chemical and kinetic analyses indicated subtle alterations in the active site microenvironment and modified ionization constants of catalytic groups.

Conclusions:

• The modification of Trp-108 significantly impacts lysozyme's catalytic activity, likely through subtle changes in the active site's microenvironment.
• The observed discrepancy in previous studies may stem from different modification byproducts or varying impacts on the active site.
• Trp-108 plays a critical role in maintaining the optimal microenvironment for lysozyme catalysis.