Development of a Potent and Functional In Vivo Peptide Competitive Inhibitor for the Toxin MazF.

Cell growth regulation granted by toxin-antitoxin systems enables bacteria to fight phage infections, evade host immune defenses, and survive antibiotic treatment. In this work, a potent and specific peptide competitive inhibitor for the Escherichia coli toxin MazF was developed and named Small Antitoxin of MazF (SamF). Employing a set of N-acetylated and C-amidated synthetic peptides, biophysical methods, biochemistry, and molecular biology techniques, we demonstrated that SamF binds tightly and with high specificity to MazF in vitro and in vivo, blocking access to the substrate binding site. Coexpression of SamF with MazF in E. coli efficiently counteracted the metabolic downregulation imposed by the toxin and the formation of antibiotic persisters. Altogether, our data uncovered a new MazF druggable site and an excellent scaffold for the design of antimicrobials. SamF is also a promising tool to study MazF in vitro and its physiological function in bacteria.