Analogs of the Autoinducer 3-Oxooctanoyl-Homoserine Lactone Strongly Inhibit Activity of the TraR Protein of Agrobacterium tumefaciens
AUTOR(ES)
Zhu, Jun
FONTE
American Society for Microbiology
RESUMO
The TraR and TraI proteins of Agrobacterium tumefaciens mediate cell-density-dependent expression of the Ti plasmid tra regulon. TraI synthesizes the autoinducer pheromone N-(3-oxooctanoyl)-l-homoserine lactone (3-oxo-C8-HSL), while TraR is an 3-oxo-C8-HSL-responsive transcriptional activator. We have compared the abilities of 3-oxo-C8-HSL and 32 related compounds to activate expression of a TraR-regulated promoter. In a strain that expresses wild-type levels of TraR, only 3-oxo-C8-HSL was strongly stimulatory, four compounds were detectably active only at high concentrations, and the remaining 28 compounds were inactive. Furthermore, many of these compounds were potent antagonists. In contrast, almost all of these compounds were stimulatory in a congenic strain that overexpresses TraR and no compound was a potent antagonist. We propose a model in which autoinducers enhance the affinity of TraR either for other TraR monomers or for DNA binding sites and that overexpression of TraR potentiates this interaction by mass action. Wild-type A. tumefaciens released a rather broad spectrum of autoinducers, including several that antagonize induction of a wild-type strain. However, under all conditions tested, 3-oxo-C8-HSL was more abundant than any other analog, indicating that other released autoinducers do not interfere with tra gene induction. We conclude that (i) in wild-type strains, only 3-oxo-C8-HSL significantly stimulates tra gene expression, while many autoinducer analogs are potent antagonists; (ii) TraR overexpression increases agonistic activity of autoinducer analogs, allowing sensitive biodetection of many autoinducers; and (iii) autoinducer stimulatory activity is potentiated by TraR overproduction, suggesting that autoinducers may shift an equilibrium between TraR monomers and dimers or oligomers. When autoinducer specificities of other quorum-sensing proteins are tested, care should be taken not to overexpress those proteins.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=107588Documentos Relacionados
- Amino-Terminal Protein Fusions to the TraR Quorum-Sensing Transcription Factor Enhance Protein Stability and Autoinducer-Independent Activity
- Binding Events of (S)-N-(3-Oxo-octanoyl)-homoserine Lactone with Agrobacterium tumefaciens Mutant Cells Studied by Saturation Transfer Difference NMR
- The crystal structure of the quorum sensing protein TraR bound to its autoinducer and target DNA
- In Situ Activation of the Quorum-Sensing Transcription Factor TraR by Cognate and Noncognate Acyl-Homoserine Lactone Ligands: Kinetics and Consequences
- Activity of the Agrobacterium Ti plasmid conjugal transfer regulator TraR is inhibited by the product of the traM gene.