The emerging antibiotic resistance requires the development of new antibiotics working on novel bacterial targets. Here, we reported an antibiotic discovery workflow by combining the cysteine-reactive compound library phenotypic screening with activity-based protein profiling, which enables the rapid identification of lead compounds as well as new druggable targets in pathogens. Compounds featuring chloromethyl ketone scaffolds exhibited a notably high hit rate against both gram-negative and gram-positive bacterial strains, but not the more commonly used warheads such as acrylamide or chloroacetamide. Target identification of the lead compound, 10-F05, revealed that its primary targets in S. flexneri are FabH Cys112 and MiaA Cys273. We validated the target relevance through biochemical and genetic interactions. Mechanistic studies revealed modification of MiaA by 10-F05 impair substrate tRNA binding, leading to decreased bacterial stress resistance and virulence. Our findings underscore chloromethyl ketone as a novel antibacterial warhead in covalent antibiotic design. The study showcases that combining covalent compound library phenotypic screening with chemoproteomics is an efficient way to identify new drug targets as well as lead compounds, with the potential to open new research directions in drug discovery and chemical biology.
