Braondon ChildersWhen ToxT “talks”……it’s all about diarrhea….
This was how Brandon Childers summarized his findings on the regulatory mechanisms mediated by a protein that controls how Vibrio cholerae causes diarrhea published recently in Journal of Molecular Biology. Brandon, a graduate student affiliated with the STCEID and the University of Texas Health Science Center at San Antonio works on Vibrio cholerae, which is a gram negative bacterium that is responsible for a devastating diarrheal disease known as cholera. The disease is marked by a sudden onset of illness, as well as the loss of large amounts of water, up to one liter per hour in severe cases, through watery stool. This sudden loss of water can result in severe dehydration, hypovolemic shock, acidosis, and eventual death from organ failure if the disease is left untreated. While the disease is almost unseen in the United States, and is effectively treated by a proper rehydration strategy, the disease remains a large problem in underdeveloped countries with little water sanitation or medical care, where the disease can produce explosive outbreaks, resulting in loss of thousands of lives.

Infection with V. cholerae begins through the consumption of contaminated water or food, where it travels through the stomach and colonizes the small intestine through the help of several factors, Toxin Coregulated Pilus (TCP) and Accessory Colonization Factors (ACF), produced by the organism. Once colonized, the bacteria begin secreting Cholera Toxin (CT), which causes the intestinal cells to excrete the large volumes of water associated with the disease. Interestingly, the three virulence factors listed above (CT, TCP, and ACF) are under the direct control of the V. cholerae protein ToxT, a transcription factor that binds to the promoter region of the genes encoding these virulence factors and activates their transcription. Deletion of the gene encoding ToxT creates an avirulent strain of V. cholerae that is unable to produce any of the necessary virulence mechanisms needed for pathogenesis.

“The main focus of my project is studying the ability of ToxT to activate virulence in V. cholerae and find methods of manipulating the protein in order to see how it functions in the bacterium. ToxT has four functions: 1) Dimerization 2) DNA Binding 3) Environmental Sensing and 4) Interaction with RNA Polymerase. We have identified residues of this protein that are critical for its function and are currently studying mutant forms of ToxT to find altered ability for any of these four functions. We are also creating strains of V. cholerae using these mutations to create possible vaccine strains capable of providing protection against the disease, which could be used to save thousands of lives” said Brandon with a smile in the middle of collecting samples for analysis.

Brandon M. Childers, Gregor G. Weber, Michael G. Prouty, Melissa M. Castaneda, Fen Peng and Karl E. Klose (2007). Identification of Residues Critical for the Function of the Vibrio cholerae Virulence Regulator ToxT by Scanning Alanine Mutagenesis. J. Mol. Biol. 367:1413-30.
doi:10.1016/j.jmb.2007.01.061