Molecular Analysis of Bacterial Adaptive Response to Host Reactive Species

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Infectious diarrhea afflicts a billion people a year and is responsible for 4% of all human deaths. Many of the 2,500 serovars of nontyphoidal Salmonella enterica are common causes of infectious diarrhea in the general population, active military servicemen and veterans. As is the case for Salmonella, the number of bacteria resistant to antibiotics is steadily increasing. Antibiotic resistance in Gram-negative bacilli is becoming a clinical problem of epic proportions with few therapeutic agents in the horizon. Future prophylactic and therapeutic approaches against drug resistant bacteria will greatly benefit from a deeper understanding of the molecular mechanisms of bacterial pathogenesis. The research of our group and many others has shown critical roles for the RNA polymerase regulatory protein DksA in the pathogenesis of multiple Gram-negative bacilli, including Salmonella, Shigella, Campylobacter, Haemophilus, Pseudomonas, and Vibrio. We have discovered that conserved cysteine residues in the DksA zinc finger are not only important for Salmonella pathogenesis but also represent a novel sensor of oxidative stress. The proposed research will test the hypothesis that the DksA zinc finger forms a stable sulfenic acid in response to low levels of oxidative stress, thereby activating transcription. At higher levels of oxidative stress, however, the oxidoreductase activity of the DnaJ chaperone catalyzes disulfide bond formation in DksA zinc finger, a redox state that represses gene transcription. This model is highly innovative because it defines DksA as a thiol multiplex with discrete regulatory outputs according to degree of oxidation of cysteine residues in the zinc finger. Our investigations will contribute to a deeper understanding of critical steps in bacterial pathogenesis and will also help the rational development of antibiotics against phylogenetically diverse Gram-negative bacilli. Based on our basic knowledge of DksA, we have already identified a drug that targets a pocket at the tip of the coiled-coil domain of this RNA polymerase regulatory protein. This novel compound has excellent antibiotic activity against Salmonella and E. coli. The proposed research will help develop and test novel antibiotics against conserved pockets in DksA. Our investigations will aid with the rational development of future therapies against a variety of Gram-negative, often antibiotic resistant, bacteria that cause high rates of morbidity and mortality in veterans and their families.