Rotein MxiE and its coregulator IpgC positively regulate the expression of variety III secretion system genes within the three-tiered VirF/VirB/MxiE transcriptional cascade. Our findings recommend a unfavorable feedback loop inside the VirF/VirB/MxiE cascade, in which MxiE and IpgC counter VirF-dependent activation on the virB promoter, as a result creating this the first characterization of negative MxiE- and IpgC-dependent regulation. Our study supplies insight into a mechanism that most likely reprograms Shigella virulence gene expression following form III secretion, which has implications for other crucial bacterial pathogens with functional homologs of MxiE and IpgC. Key phrases Shigella, MxiE, IpgC, VirF, unfavorable AraC-like regulator, ospD1 promoter,Editor Patricia A. Champion, University of Notre Dame Copyright 2022 American Society for Microbiology. All Rights Reserved. Address correspondence to Helen J. Wing, [email protected]. Present address: Joy A. McKenna, Department of Microbiology and Immunology, Stanford School of Medicine, Stanford University, Stanford, California, USA. The authors declare no conflict of interest. Received 19 April 2022 Accepted 23 May possibly 2022 Published 15 JunevirB promoter, sort III secretion system, damaging feedback loop, form III secretionMany Gram-negative bacterial pathogens, which includes Shigella species, use form III secretion systems (T3SS) to straight inject virulence proteins, known as effectors, into host cells to invade and/or subvert host cell machinery (1). With out a functionalJuly 2022 Volume 204 Issue10.1128/jb.00137-Negative Feedback Loop Regulates T3SS-Encoding GenesJournal of BacteriologyT3SS, these pathogens are frequently avirulent in animal infection models (two). Often, genes encoding the T3SS are transcriptionally activated by members of the AraC family of transcriptional regulators (AFTRs) (3, 4). Examples of AFTRs that regulate T3SSencoding genes are VirF (5, 6) and MxiE (7, eight) in Shigella species, BsaN in Burkholderia pseudomallei (9), and InvF in Salmonella enterica serovars Typhi and Typhimurium (10). With the well-characterized proteins within the big AraC household of transcriptional regulators ( 830 proteins [11]), most are described as activators that regulate the transcription of genes involved in carbon metabolism, pressure response, or pathogenesis (12). A distinguishing feature of AFTRs is actually a conserved C-terminal DNA-binding domain comprised of two helix-turn-helix motifs (12, 13). Because of the higher homology of this domain, the DNA-binding and/or regulatory activities of some AFTRs have already been shown to be interchangeable when substituted for each and every other (146).AZD4635 Purity & Documentation In contrast, the N-terminal domains of AFTRs are functionally variable and involved in dimerization and/or ligand binding (4, 12, 17, 18).MKC-1 Cancer Due to the notorious insolubility of purified AFTRs in vitro, functional characterizations for the mechanism(s) of AFTR transcriptional regulation have verified challenging (19).PMID:24761411 In Shigella flexneri, a causal agent of bacillary dysentery, a T3SS is used to inject two distinct waves of effectors to invade human colonic epithelial cells and adopt intracellular residency (204). Most genes encoding the T3SS (e.g., apparatus, effectors, and regulators) are clustered within the 31-kb ipa mxi spa operons (25, 26) around the massive (;220 kb) virulence plasmid pINV (279). The pINV-associated virulence genes are regulated by the three-tiered VirF/VirB/MxiE transcriptional cascade, of which the firstand third-tier regulators VirF and MxiE be.
