Phenotypic characterization of a Salmonella typhimurium dsbA null mutant and identification of factors that regulate the expression of the disulfide oxidoreductase DsbA (Salmonella typhimurium)

Protein disulfide bond formation in Gram negative bacteria has been shown to be catalyzed by the various periplasmic and membrane proteins that make up a disulfide bond formation (dsb) system. We are studying the contribution of these periplasmic foldases to the folding of proteins in Salmonella typhimurium. The gene coding for the key enzyme in this system, disulfide oxidoreductase DsbA, had been cloned in our laboratory and it has been determined that DsbA is regulated in a growth-phase dependent manner in S. typhimurium . In this study three aspects of the dsb system were further explored. The role of DsbA in the phenomenon of resistance to cationic peptide exhibited by this organism was examined.; It was determined that the S. typhimurium dsbA null strain is more susceptible than the wild type strain to the effects of protamine sulfate, a cationic antimicrobial peptide that is considered to be a functional analogue of defensin. Although the exact mechanism of susceptibility is unknown, the disruption of disulfide bond formation was shown to affect the secreted, envelope and outer membrane protein profiles of the dsbA null strain. The approaches we undertook for the identification of the dsbB gene proved unsuccessful, however, we now know that a dsbB homologue does exist in S. typhimurium as it has been sequenced by the Washington University Genome Sequencing Centre. (Abstract shortened by UMI.)...