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Tethered thiazolidinone dimers as inhibitors of the bacterial type III secretion system.

ABSTRACT: Disruption of protein-protein interactions by small molecules is achievable but presents significant hurdles for effective compound design. In earlier work we identified a series of thiazolidinone inhibitors of the bacterial type III secretion system (T3SS) and demonstrated that this scaffold had the potential to be expanded into molecules with broad-spectrum anti-Gram negative activity. We now report on one series of thiazolidinone analogs in which the heterocycle is presented as a dimer at the termini of a series of linkers. Many of these dimers inhibited the T3SS-dependent secretion of a virulence protein at concentrations lower than that of the original monomeric compound identified in our screen.

SUBMITTER: Kline T

PROVIDER: S-EPMC2680725 | biostudies-literature | 2009 Mar

REPOSITORIES: biostudies-literature

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Tethered thiazolidinone dimers as inhibitors of the bacterial type III secretion system.

Kline Toni T Barry Kathleen C KC Jackson Stona R SR Felise Heather B HB Nguyen Hai V HV Miller Samuel I SI

Bioorganic & medicinal chemistry letters 20090120 5

Disruption of protein-protein interactions by small molecules is achievable but presents significant hurdles for effective compound design. In earlier work we identified a series of thiazolidinone inhibitors of the bacterial type III secretion system (T3SS) and demonstrated that this scaffold had the potential to be expanded into molecules with broad-spectrum anti-Gram negative activity. We now report on one series of thiazolidinone analogs in which the heterocycle is presented as a dimer at the ...[more]

PMID: 19195888

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Project description:BackgroundType III secretion systems are a common virulence mechanism in many Gram-negative bacterial pathogens. These systems use a nanomachine resembling a molecular needle and syringe to provide an energized conduit for the translocation of effector proteins from the bacterial cytoplasm to the host cell cytoplasm for the benefit of the pathogen. Prior to translocation specialized chaperones maintain proper effector protein conformation. The class II chaperone, Invasion plasmid gene (Ipg) C, stabilizes two pore forming translocator proteins. IpgC exists as a functional dimer to facilitate the mutually exclusive binding of both translocators.ResultsIn this study, we present the 3.3 A crystal structure of an amino-terminally truncated form (residues 10-155, denoted IpgC10-155) of the class II chaperone IpgC from Shigella flexneri. Our structure demonstrates an alternative quaternary arrangement to that previously described for a carboxy-terminally truncated variant of IpgC (IpgC1-151). Specifically, we observe a rotationally-symmetric "head-to- head" dimerization interface that is far more similar to that previously described for SycD from Yersinia enterocolitica than to IpgC1-151. The IpgC structure presented here displays major differences in the amino terminal region, where extended coil-like structures are seen, as opposed to the short, ordered alpha helices and asymmetric dimerization interface seen within IpgC1-151. Despite these differences, however, both modes of dimerization support chaperone activity, as judged by a copurification assay with a recombinant form of the translocator protein, IpaB.ConclusionsFrom primary to quaternary structure, these results presented here suggest that a symmetric dimerization interface is conserved across bacterial class II chaperones. In light of previous data which have described the structure and function of asymmetric dimerization, our results raise the possibility that class II chaperones may transition between asymmetric and symmetric dimers in response to changes in either biochemical modifications (e.g. proteolytic cleavage) or other biological cues. Such transitions may contribute to the broad range of protein-protein interactions and functions attributed to class II chaperones.

Project description:Most pathogenic bacteria deliver virulence factors into host cytosol through type III secretion systems (T3SS) to perturb host immune responses. The expression of T3SS is often repressed in rich medium but is specifically induced in the host environment. The molecular mechanisms underlying host-specific induction of T3SS expression is not completely understood. Here we demonstrate in Xanthomonas citri that host-induced phosphorylation of the ATP-dependent protease Lon stabilizes HrpG, the master regulator of T3SS, conferring bacterial virulence. Ser/Thr/Tyr phosphoproteome analysis revealed that phosphorylation of Lon at serine 654 occurs in the citrus host. In rich medium, Lon represses T3SS by degradation of HrpG via recognition of its N terminus. Genetic and biochemical data indicate that phosphorylation at serine 654 deactivates Lon proteolytic activity and attenuates HrpG proteolysis. Substitution of alanine for Lon serine 654 resulted in repression of T3SS gene expression in the citrus host through robust degradation of HrpG and reduced bacterial virulence. Our work reveals a novel mechanism for distinct regulation of bacterial T3SS in different environments. Additionally, our data provide new insight into the role of protein posttranslational modification in the regulation of bacterial virulence.IMPORTANCE Type III secretion systems (T3SS) are an essential virulence trait of many bacterial pathogens because of their indispensable role in the delivery of virulence factors. However, expression of T3SS in the noninfection stage is energy consuming. Here, we established a model to explain the differential regulation of T3SS in host and nonhost environments. When Xanthomonas cells are grown in rich medium, the T3SS regulator HrpG is targeted by Lon protease for proteolysis. The degradation of HrpG leads to downregulated expression of HrpX and the hrp/hrc genes. When Xanthomonas cells infect the host, specific plant stimuli can be perceived and induce Lon phosphorylation at serine 654. Phosphorylation on Lon attenuates its proteolytic activity and protects HrpG from degradation. Consequently, enhanced stability of HrpG activates HrpX and turns on bacterial T3SS in the host. Our work provides a novel molecular mechanism underlying host-dependent activation of bacterial T3SS.

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Tethered thiazolidinone dimers as inhibitors of the bacterial type III secretion system.

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Tethered thiazolidinone dimers as inhibitors of the bacterial type III secretion system.

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