IGEM:MIT/2005/*ToxR* info, etc.

Pathway summary coming up soon.. if impatient, read the 2nd paper.

• ToxR/lambda phage
  • Read the intro to this article (not just the abstract). Its VERY informative --> good for beginners.
• Co-regulation of cholera toxin genes
  • ToxR’s role is signal transduction through the membrane. It’s mechanism of action is thought to be the dimerization of ToxR (DiRita & Mekalanos, 1991). This mechanism of an extracellular protein causing a transmembrane protein to complex and activate transcription is fairly novel among bacterial transcriptional regulation systems.]
• Synthesis of cholera toxin is positively regulated at the transcriptional level by toxR.
  • 1984 paper, mostly stuff we know, but in being sensitive to manipulating cells that can have negative human affects: "Southern blot analysis suggests
  • that all V. chokrae, including nontoxinogenic strains, have the toxR gene. Moreover, nontoxinogenic strains not only lack the structural genes for cholera toxin but also sequences associated with the larger 7-kilobase ctx genetic element." No, We Don't Have to Work With Virulent Cholera To Use ToxR.
• Invivo evidence for TonB dimerization with ToxR
  • I've only read the abstract, but TonB is a protein on the surface of E.Coli
  • Dimerization of ToxR causes ctx to be produced. But in E.Coli, this dimerization is studied by placing a lacZ (or other reporter gene) under the ctx promoter. So we don't need to be concerned about virulence factors.
• Co-ordinate expression of virulence genes by ToxR in Vibrio cholerae.
  • take home message: ToxR directly promotes some stuff (which includes production of ToxT). ToxT then directly promotes other stuff. ToxR can be a stand alone transcriptional factor.
• Changes in the periplasmic linker and in the expression level affect the activity of ToxR and lambda-ToxR fusion proteins in Escherichia coli.
  • Only read the abstract
  • These guys used ToxR-lambda phage repressor as a dimerization reporter
  • they constructed plasmids for various transmembrane fusion proteins.
  • Current status: reading it to summarize
  • Uh oh, problem: this article says: "the authors suggested that dimerization is not a requirement for ToxR activity in E. coli 10. Someone should get on the referenced paper right now and find out why this is a problem.
    • • best I can tell, the reference claims that the ToxR periplasmic domain could be replaced with a few other dimers and a toxr_like monomer. Further anaylisis showed that this substitution only sort of worked. The "correct" ToxR confirmation may be more important for function says the paper. This point is worth remembering, but likely not a game-breaker.