Enhanced bacteriolytic activity of hen egg-white lysozyme due to conversion of Trp62 to other aromatic amino acid residues

Tryptophan at the 62nd position (Trp62) of hen egg-white lysozyme is an amino acid residue whose action is essential for its enzymatic activity. Its indole ring may possibly come into direct contact with sugar residues of the substrate, and thus contribute significantly to substrate binding. For further elucidation of its role in catalytic processes, this amino acid was converted to other aromatic residues, such as Tyr, Phe, and His, by site-directed mutagenesis. All the mutations were found to enhance the bacteriolytic activity but to decrease the hydrolytic activity toward an artificial substrate, glycol chitin. Such a change in substrate preference appears remarkable considering the smaller size of the aromatic residue on the mutant enzyme at the 62nd position.