A novel LysinB from an F2 sub-cluster mycobacteriophage RitSun

With the growing antibiotic resistance in mycobacterial species posing a significant threat globally, there is an urgent need to find alternative solutions. Bacteriophage-derived endolysins aid in releasing phage progeny from the host bacteria by attacking the cell wall at the end of their life cycle. Endolysins are attractive antibacterial candidates due to their rapid lytic action, specificity and low risk of resistance development. In mycobacteria, owing to the complex, hydrophobic cell wall, mycobacteriophages usually synthesize two endolysins: LysinA, which hydrolyzes peptidoglycan; LysinB, which delinks mycolylarabinogalactan from peptidoglycan and releases mycolic acid. In this study, we conducted domain analysis and functional characterization of a recombinant LysinB from RitSun, an F2 sub-cluster mycobacteriophage. Several properties of RitSun LysinB are important as an antimycobacterial agent: its ability to lyse Mycobacterium smegmatis from without, a specific activity of 1.36 U/mg, higher than the reported ones and its inhibitory effect on biofilm formation. Given the impervious nature of the mycobacterial cell envelope, native endolysins ability to damage cells on exogenous applications warrants further investigation. A molecular dissection of RitSun LysinB to identify its cell wall destabilizing sequence could be utilized to engineer other native lysins as fusion proteins and expand their activity profile.