title: Inhibition of the Agrobacterium tumefaciens TraR quorum-sensing regulator. Interactions with the TraM anti-activator.
abstract: The Agrobacterium tumefaciens quorum-sensing transcriptional regulator TraR and its inducing ligand 3-oxo-octanoyl-l-homoserine lactone control conjugal transfer of the tumor-inducing plasmid, the primary virulence factor responsible for crown gall disease of plants. This regulatory system enables A. tumefaciens to express its conjugal transfer regulon preferentially at high population densities. TraR activity is antagonized by a second tumor-inducing plasmid-encoded protein designated TraM. TraM and TraR are thought to form an anti-activation complex that prevents TraR from recognizing its target DNA-binding sites. The formation and inhibitory function of the TraM-TraR anti-activation complex was analyzed using several different assays for protein-protein interaction, including surface plasmon resonance. The TraR-TraM complex forms readily in solution and is extremely stable (K(D) of 1-4 x 10(-9) m). Directed mutational analysis of TraM identified a number of amino acids that play important roles in the inhibition of TraR, clustering in two regions of the protein. Interestingly, several mutants were identified that proficiently bound TraR but were unable to inhibit its activity. This observation suggests a mechanistic separation between the initial assembly of the complex and conversion of TraR to an inactive form.
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana 47405, USA.
authors.forename: A
authors.initials: A
authors.lastname: Swiderska
authors.forename: A K
authors.initials: AK
authors.lastname: Berndtson
authors.forename: M R
authors.initials: MR
authors.lastname: Cha
authors.forename: L
authors.initials: L
authors.lastname: Li
authors.forename: G M
authors.initials: GM
authors.lastname: Beaudoin
authors.forename: J
authors.initials: J
authors.lastname: Zhu
authors.forename: C
authors.initials: C
authors.lastname: Fuqua
mesh_terms: D016960:Agrobacterium tumefaciens / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D010941:Plant Tumors / Q000382:microbiology; D010957:Plasmids; D011485:Protein Binding; D020349:Surface Plasmon Resonance; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C080512:TraR protein, Agrobacterium tumefaciens; D014157:Transcription Factors; C074281:TraM protein, bacterial