Flexibility analysis of activity-enhanced mutants of bacteriophage T4 lysozyme

Genetically Encoded Biosensor-Based Screening for Directed Bacteriophage T4 Lysozyme Evolution

Lysozyme is widely used as a model protein in studies of structure–function relationships. Recently, lysozyme has gained attention for use in accelerating the degradation of secondary sludge, which mainly consists of bacteria. However, a high-throughput screening system for lysozyme engineering has not been reported. Here, we present a lysozyme screening system using a genetically encoded biosensor. We first cloned bacteriophage T4 lysozyme (T4L) into a plasmid under control of the araBAD promoter. The plasmid was expressed in Escherichia coli with no toxic effects on growth. Next, we observed that increased soluble T4L expression decreased the fluorescence produced by the genetic enzyme screening system. To investigate T4L evolution based on this finding, we generated a T4L random mutation library, which was screened using the genetic enzyme screening system. Finally, we identified two T4L variants showing 1.4-fold enhanced lytic activity compared to native T4L. To our knowledge, this is the first report describing the use of a genetically encoded biosensor to investigate bacteriophage T4L evolution. Our approach can be used to investigate the evolution of other lysozymes, which will expand the applications of lysozyme.

Examining the molecular characteristics of glycoside hydrolase family 20 β-N-acetylglucosaminidases with high activity

β-N-Acetylglucosaminidases (GlcNAcases) possess many important biological functions and are used for promising applications that are often hampered by low-activity enzymes. We previously demonstrated that most GlcNAcases of the glycoside hydrolase (GH) family 20 showed higher activities than those of other GH families, and we presented two novel GH 20 GlcNAcases that showed higher activities than most GlcNAcases. A highly flexible structure, which was attributed to the presence of to a high proportion of random coils and flexible amino acid residues, was presumed to be a factor in the high activity of GH 20 GlcNAcases. In this study, we further hypothesized that two special positions might play a key role in catalytic activity. The increase in GH 20 GlcNAcase activity might correspond to the increased structural flexibility and substrate affinity of the two positions due to an increase in random coils and amino acid residues, notably acidic Asp and Glu.