Regulatory mechanisms of type III secretion system by molecular chaperones and proteases in Salmonella enterica serovar Typhimurium.

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Salmonella enterica serovar Typhimurium, similar to various facultative intracellular pathogens, has been shown to respond to the hostile conditions inside macrophages of the host organism by inducing stress proteins. The stress proteins are functionally divided into two groups, molecular chaperones and proteases. We showed molecular chaperones and proteases have an important function for the Salmonella Pathogenicity.(1)Regulatory mechanisms of type III secretion system (TTSS) by AAA+ protease familyWe showed that the heat shock proteases ClpXP and Lon are essentially involved in systemic infection with S.enterica serovar Typhimurium in BALB/c mice. ClpXP and Lon are required for the survival and growth of S.enterica serovar Typhimurium within macrophages. We reported that ClpXP and Lon control the expression of two TTSSs in S.enterica serovar Typhimurium in which one is encoded by flagellar regulon and another is by Salmonella Pathogenicity Island 1(SPI1).(2)Regulatory mechanisms of TTSS by molecular chaperoneMacrophage survival assays revealed that the DnaK/DnaJ-depleted mutant could not survive or proliferate at all within macrophages. This mutant could neither invade cultured epithelial cells nor secrete any of the invasion proteins encoded within SPI1. We also showed that the DnaK/DnaJ-depleted mutant could not secrete flagellar proteins and SPI2 effector proteins encoded by TTSSs.(3)Development of Salmonella live vaccine.Immunization with the ClpXP-or Lon-deficient strain protected mice against oral challenge with the S. enterica serovar Typhimurium virulent strain. Both the challenged virulent and immunized avirulent salmonellae were completely cleared from the spleen, mesenteric lymph nodes, Peyer's patches, and even cecum 5 days after the challenge. Our data indicated that Salmonella with a disruption of the ATP-dependent protease ClpXP or Lon could be useful in developing a live vaccine strain.