Team:EPF Lausanne/Data

From 2014.igem.org

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<p>Hello</p>
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<h3><b>Experiment 2: </b>CpxR dimerization & Dimerization Orientation </h3>
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<p>
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<u>Introduction</u> <br />
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CpxR is the relay protein in the stress resonsive CpxAR two component regulatory system. It has been shown by split beta galactosidase assay that CpxR dimerizes when phosphorylated (activated) in yersinia pseudotuberculosis. Moreover, following other in vitro FRET studies, it was shown that E.Coli CpxR interacted with itself.  We therefore hypothesised that dimerization would also be true in vivo in E.Coli.</p>
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<p>
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<u>Aim</u> <br />
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This experiment aimed to determine if and how CpxR dimerised in vivo in E.Coli. This experiment intended to get a first idea of the real-time temporal dynamics of the activation of CpxR (the cytoplasmic relay protein of the CpxA-R pathway) by KCl stress via CpxA (the periplasmic sensor protein of the CpxA-R pathway). This experiment is a first of its kind.
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</p>
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<p>
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<u>Methods</u> <br />
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To evaluate if and how CpxR dimerized under KCl stress, we built by gibson assembly four constructs with the various possible orientations that the split IFP1.4 fragments could have with CpxR: IFP[1] and IFP[2] on the N-terminus of CpxR, IFP[1] on the N-terminus of CpxR and IFP[2] on the C-terminus of CpxR, and finally IFP[1] and IFP[2] on the N-terminus of CpxR. The split IFP fragments were provided by the Michnick Lab, and the CpxR coding region was amplified by PCR from extracted E.Coli genome (Bacterial Genomic Miniprep Kit from Sigma Aldrich). The protocol for stressing the cells and reading the fluorescence can be downloaded <a href="https://static.igem.org/mediawiki/2014/a/a5/EPFL_Protocol_IFP_stress_1.pdf">here</a>.
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</p>
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<p>
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<u>Results</u> <br />
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As seen in the graph bellow, induction of the signal was done at minute 24 (marked via a vertically spoted line). The construct with IFP fragments on the C-termina responded immediately to stress. In a fact we observed a 3 fold signal increase in 2 minutes. All other constructs we observed a low baseline signal non responsive to KCl stress. It is to be noted that the C-termina constructs always had higher signal levels than the other constructs. This leads us to believe that the PBS used to resuspend our cultures led to small levels of stress (the PBS we use does not contain KCl but traces of NaCl). The 30-fold signal increase from the baseline allows us to assert that our constructs responds to KCl stress.
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</p>
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<p>
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<u>Discussion</u> <br />
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We successfully proved that CpxR dimerized in vivo and that dimerization led to close interaction of its C-terminus. This finding suggests that CpxR binds via its C-termina. This leads us to hypothesise that the CpxR dimerisation mechanisms is the same for other members of the highly conserved OmpR/PhoB subfamily. This hypothesis could allow the development of similar system that could the study other components of the OmpR/PhoB subfamily and thus lead to a new generation of highly senstitive and reactive biosensors.
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</p>
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<div class="container cntr">
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<img src="https://static.igem.org/mediawiki/2014/c/c2/KCL_Construct_Comparison.jpg" alt="Construct Comparison">
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</div>
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<br /><br />

Revision as of 14:58, 11 October 2014

Experiment 2: CpxR dimerization & Dimerization Orientation

Introduction
CpxR is the relay protein in the stress resonsive CpxAR two component regulatory system. It has been shown by split beta galactosidase assay that CpxR dimerizes when phosphorylated (activated) in yersinia pseudotuberculosis. Moreover, following other in vitro FRET studies, it was shown that E.Coli CpxR interacted with itself. We therefore hypothesised that dimerization would also be true in vivo in E.Coli.

Aim
This experiment aimed to determine if and how CpxR dimerised in vivo in E.Coli. This experiment intended to get a first idea of the real-time temporal dynamics of the activation of CpxR (the cytoplasmic relay protein of the CpxA-R pathway) by KCl stress via CpxA (the periplasmic sensor protein of the CpxA-R pathway). This experiment is a first of its kind.

Methods
To evaluate if and how CpxR dimerized under KCl stress, we built by gibson assembly four constructs with the various possible orientations that the split IFP1.4 fragments could have with CpxR: IFP[1] and IFP[2] on the N-terminus of CpxR, IFP[1] on the N-terminus of CpxR and IFP[2] on the C-terminus of CpxR, and finally IFP[1] and IFP[2] on the N-terminus of CpxR. The split IFP fragments were provided by the Michnick Lab, and the CpxR coding region was amplified by PCR from extracted E.Coli genome (Bacterial Genomic Miniprep Kit from Sigma Aldrich). The protocol for stressing the cells and reading the fluorescence can be downloaded here.

Results
As seen in the graph bellow, induction of the signal was done at minute 24 (marked via a vertically spoted line). The construct with IFP fragments on the C-termina responded immediately to stress. In a fact we observed a 3 fold signal increase in 2 minutes. All other constructs we observed a low baseline signal non responsive to KCl stress. It is to be noted that the C-termina constructs always had higher signal levels than the other constructs. This leads us to believe that the PBS used to resuspend our cultures led to small levels of stress (the PBS we use does not contain KCl but traces of NaCl). The 30-fold signal increase from the baseline allows us to assert that our constructs responds to KCl stress.

Discussion
We successfully proved that CpxR dimerized in vivo and that dimerization led to close interaction of its C-terminus. This finding suggests that CpxR binds via its C-termina. This leads us to hypothesise that the CpxR dimerisation mechanisms is the same for other members of the highly conserved OmpR/PhoB subfamily. This hypothesis could allow the development of similar system that could the study other components of the OmpR/PhoB subfamily and thus lead to a new generation of highly senstitive and reactive biosensors.

Construct Comparison


Sponsors