Helicobacter pylori (H. pylori) is a gram-negative pathogenic bacterium that infects half of the world’s population. It resides in the human stomach, where it survives extremely acidic conditions. Efficient colonization by H. pylori requires urease and hydrogenase enzymes, both of which utilize nickel as a cofactor. The intracellular level of nickel in H. pylori is strictly maintained by a nickel-responsive transcription factor, HpNikR, which acts as a master regulator to control both activation of the urease genes and repression of a variety of other genes including its own. In addition to its role in nickel homeostasis, HpNikR has been implicated in the adaptive response of H. pylori to acidic environmental conditions.
In this work, two representative genes, ureA and nikR, are confirmed to be regulated by HpNikR directly in response to changes in nickel concentration, with HpNikR binding to the promoter region of each gene. The binding sequences on the two promoters are distinct from each other and no consensus sequence could be identified from them. The binding affinity of HpNikR to the ureA promoter is much tighter than to the nikR promoter. Another signal that can activate the DNA-binding activity of HpNikR is a change in pH. Once HpNikR is activated by proton binding, it binds to the ureA promoter independently of nickel concentration, but still binds to the nikR promoter in a nickel-dependent manner. Several amino acids at the N-terminus of HpNikR, including Asp7, Asp8 and Lys6, are critical for the specific response of HpNikR to pH changes. In addition, the binding of HpNikR to distinct DNA sequences induces different degrees of DNA bending, which provides another possible means of gene regulation by HpNikR. The ability of HpNikR to differentially regulate distinct genes in response to several signals allows a graduated level of control of gene expression by HpNikR. In vivo studies to evaluate the physiological relevance of the above in vitro results have been initiated.
Given the relatively low abundance of transcription factors in H. pylori, information about the effects of nickel and pH on HpNikR in vivo is important for understanding the multifaceted roles of HpNikR in fine-tuning the physiology of this organism. Ultimately this study may provide us with a better idea of how to control H. pylori-caused diseases.
| Identifer | oai:union.ndltd.org:TORONTO/oai:tspace.library.utoronto.ca:1807/26287 |
| Date | 18 February 2011 |
| Creators | Li, Yanjie |
| Contributors | Zamble, Deborah |
| Source Sets | University of Toronto |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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