A small molecule, C24H17ClN4O2S, inhibits the function of the type III secretion system in Salmonella Typhimurium

Abstract

Background Salmonella enterica serovar Typhimurium (S. Typhimurium) causes gastroenteritis and diarrhea in humans and food-producing animals. The type III secretion system (T3SS) has been known to be a potent virulence mechanism by injecting effector proteins into the cytosol of host cells. S. Typhimurium encodes two T3SSs by Salmonella pathogenicity islands 1 and 2. Previous studies showed that T3SS shared a potent virulence mechanism and molecular structure among several gram-negative bacteria. Therefore, T3SS has been identified as an attractive target in the development of novel therapeutics for the treatment of bacterial infections. Several studies reported that small-molecule compounds are able to inhibit functions of bacterial T3SSs. A small molecule, C24H17ClN4O2S, has been shown the ability to inhibit the activity of Yersinia pestis T3SS ATPase, YscN, resulting to block the secretion of effector proteins. In this study, we studied the effects and mechanism for SPI-1 T3SS inhibition of this compound in S. Typhimurium. Results We demonstrated that this compound prohibited the secretion of effector proteins from Salmonella via SPI-1 T3SS at 100 μM. As the result, bacterial invasion ability into epithelial cell cultures was reduced. In contrast with previous study, the C24H17ClN4O2S molecule did not inactivate the activity of SPI-1 T3SS ATPase, InvC, in Salmonella. However, we studied the global cellular effects of S. Typhimurium after being treated with this compound using a quantitative proteomic technique. These proteomic results showed that the main SPI-1 transcription regulator, InvF, and two effector proteins, SipA and SipC, were reduced in bacterial cells treated with the compound. Conclusions It may explain that action of the small-molecule compound, C24H17ClN4O2S, for blocking the secretion of SPI-1 T3SS in Salmonella is through inhibition of SPI-1 regulator, InvF, expression. Further studies are necessary to identify specific mechanisms for inhibition between this small-compound and InvF SPI-1 regulator protein.

Research Progress on Small Molecular Inhibitors of the Type 3 Secretion System

“…A similar development strategy could be applied to other human pathogens that contain T3SSs, including enteropathogenic E. coli , S. flexneri , S. typhimurium , and Burkholderia mallei/pseudomallei species [ 125 ]. Recently, Boonyom et al [ 127 ] found that compound 25 interdicted the secretion of the effector protein SPI-1 of Salmonella T3SS at a concentration of 100 μM. The compound also attenuated the bacterial invasion of epithelial cells.…”

In Silico Screening and Evolution of Promising Novel Anti-Virulents Against Salmonella ATPase

“…In addition, inhibition of T3SS ATPase avoids the risk of cross-reaction between T3SS ATPase inhibitors and human ATPase enzymes because bacterial ATPase and human ATPase share less than 25% of their sequences and their active sites are structurally different 5 . Though there are many existing inhibitors of Salmonella T3SS, none have been shown to target the InvC protein vital for combating antibacterial resistance 20,21,22,23,24 .…”