Identification of inhibitors of the Salmonella FraB deglycase, a drug target.

Nontyphoidal Salmonella is one of the most prevalent causes of human foodborne illnesses worldwide, with no narrow-spectrum antibiotics or vaccines available. Here, we seek to address this gap. During the host inflammatory response, Salmonella metabolizes fructose-asparagine as a nutrient using proteins encoded in the fra operon. Deletion of fraB leads to a build-up of 6-phosphofructose-aspartate, the substrate of FraB, and intoxicates Salmonella. Because fra genes are absent in mammals and most members of the human gut microbiome, FraB inhibitors are expected to have limited off-target effects and offer prospects as potential therapeutics. To identify such inhibitors, we conducted a high-throughput screening of small-molecule libraries using a FraB activity-based biochemical assay. We screened 131,165 compounds and identified 126 hits that could be obtained commercially for further characterization. When tested at 25 μm inhibitor in the presence of 1 mm 6-phosphofructose-aspartate, FraB activity was reduced ~ 30-100% by 65 compounds. Guided by preliminary cell-based data, we further characterized six compounds (one triazolidine, two thiadiazolidines, and three triazolothiadiazoles) and found them to exhibit IC