Biochemical Characterizations of the Putative Amidase Endolysin Ecd18980 Catalytic Domain from Clostridioides...

Clostridioides difficile is the major causative pathogen of pseudomembranous colitis, and novel antimicrobial agents are required for treatment. Phage-derived endolysins exhibiting species-specific lytic activity have potential as novel antimicrobial agents. We surveyed the genome of C. difficile strain 630 and identified a gene encoding an endolysin, Ecd18980, which has an amidase_3 domain at the N-terminus but unknown C-terminal domain. The genes encoding Ecd18980 and its catalytic domain (Ecd18980CD) were cloned and expressed in Escherichia coli as N-terminal histidine-tagged proteins. These purified proteins showed lytic activity against C. difficile. Ecd18980CD showed higher lytic activity than the wild-type enzyme and near-specific lytic activity against C. difficile. This species specificity is thought to depend on substrate cleavage activity rather than binding. We also characterized the biochemical properties of Ecd18980CD, including optimal pH, salt concentration, and thermal stability.