Difference between revisions of "Part:BBa K1031300"

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=='''Introduction'''==
 
=='''Introduction'''==
HbpR (For more details:http://2013.igem.org/Team:Peking/Project/BioSensors/HbpR) is 54-dependent transcriptional factor belonging to NtrC family of prokaryotic transcriptional activators. It shares a high homology to members of the XylR/DmpR subclass. HbpR was found in Pseudomonas azelaica. which can use 2-hydroxybiphenyl (2-HBP) and 2, 2’-dihydroxybiphenyl as sole carbon and energy sources through enzymes encoded by hbpCAD functioning in meta-cleavage pathway.
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HbpR (For more details:http://2013.igem.org/Team:Peking/Project/BioSensors/HbpR) is a 63-kDa prokaryotic transcriptional activators from NtrC family. It shares a highly conserved homology to members of the XylR/DmpR subclass. HbpR was found in <i>Pseudomonas azelaica</i><html><a href="#ReferenceHbpR"><sup>[1]</sup></a></html>, which can use 2-hydroxybiphenyl (2-HBP) and 2, 2’-dihydroxybiphenyl as sole carbon and energy sources through enzymes encoded by <i>hbpCAD</i> operon in meta-cleavage pathway.
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<p><b>Metabolic Operon</b></p>
 
<p><b>Metabolic Operon</b></p>
 
<img src="https://static.igem.org/mediawiki/2013/3/36/Peking2013_HbpR_Overview.png" style="width:800px;margin-left:60px"  ></a>
 
<img src="https://static.igem.org/mediawiki/2013/3/36/Peking2013_HbpR_Overview.png" style="width:800px;margin-left:60px"  ></a>
  
<p style="text-align:center"><b>Fig.1</b> Operon and pathway of HboR(a) Operon of HbpR. Orange rectangle shows hbpR gene. Blue and green rectangles show hbpCA and hbpD genes controled by PC and PD respectively. The orange rectangle show hbpR gene which encodes HbpR protein. When exposed to effector 2-hydroxybiphenyl, HbpR will activate PC and PD. (b) Pathway for the primary metabolism of 2-hydroxybiphenyl and 2-propylphenol in<i> P. azelaica</i> HBP1. The enzymes for each step are also indicated.
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<p style="text-align:center"><b>Figure.1</b> (<b>a</b>) HbpR as the regulator to control the expression of <i>hbp</i> operon. Blue and green rectangles denote <i>hbpCA</i> and <i>hbpD</i> genes controled by <i>P<sub>C</sub></i> and <i>P<sub>D</sub></i>, respectively. The orange rectangle show the <i>hbpR</i> gene which encodes HbpR protein. When exposed to the effectors, such as 2-hydroxybiphenyl, HbpR will activate transcription at <i>P<sub>C</sub></i> and <i>P<sub>D</sub></i>. (<b>b</b>) Pathway for the primary metabolism of 2-hydroxybiphenyl and 2-propylphenol in <i>P. azelaica</i> HBP1. The enzymes for each step of the degradation are also indicated.
 
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<p>
 
<b>Protein Domains</b></p>
 
<b>Protein Domains</b></p>
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<img src="https://static.igem.org/mediawiki/igem.org/9/94/HbpR_Figure3_2013Peking_WH.png", width=400px;/>
 
<img src="https://static.igem.org/mediawiki/igem.org/9/94/HbpR_Figure3_2013Peking_WH.png", width=400px;/>
  
<p style="position:absolute; top: 600px; left: 450px;"><b>Fig.2</b> Four domains of HbpR protein. A domain is sensing domain, conformation change may happen with inducer's binding. B domain is a linker. C domain contains an AAA ATPase motif. It has the capacity to hydrolyze ATP and to interact with sigma54 RNA polymerase. D domain binds to DNA via a typical helix-turn-helix motif.  
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<p style="position:absolute; top: 600px; left: 450px;"><b>Figure.2</b> Schematics for the domain organization of HbpR protein. N represents the N-terminal of HbpR and C represent the C-terminal. A, B, C and D denote 4 domains of HbpR, respectively, and the numbers below them denote domain boundaries at amino-acid-sequence resolution.C-domain contains an AAA+ ATPase motif<a href="#ReferenceHbpR"><sup>[2]</sup></a>. It has the ability to hydrolyze ATP and to interact with &sigma;<sup>54</sup> to recruit RNA polymerase for transcription activation. D-domain binds to DNA via a typical helix-turn-helix motif. A-domain is necessary for the recognition of aromatic effector molecules to activate transcription.
 
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<p id="FigureHbpR3"style="position:absolute; top:800px; left:450px; height:300px;">
 
<p id="FigureHbpR3"style="position:absolute; top:800px; left:450px; height:300px;">
<B>Fig.3</B> Regions containing the binding sites for HbpR (UAS) are shown within boxes in the sequence. Sequence numbers refer to the locations of the transcriptional start sites of hbpC and hbpD. HbpR binds to UAS C-1 and UAS C-2. The 32-bp space between the centers of UASs C-1 and C-2 is critical for cooperative interactions. when the UASs C-1/C-2 are deleted and UASs C-3/C-4 are placed in an appropriate position with respect to the promoter region, the hbpC promoter is still inducible with 2-HBP, albeit at a lower level. The presence of UAS pair C-3/C-4 mediated a higher promoter activity for transcription of hbpR.  
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<B>Figure.3</B> The sequences preceding <i>hbpC</i> promoter contains the binding sites for HbpR (UAS,Upstream Activating Sequences<a href="#ReferenceHbpR"><sup>[3]</sup></a>, boxed in red). Sequence numbers denote the locations of UASs relative to the transcriptional start site of hbpC and hbpD. HbpR binds to UAS C-1 and UAS C-2. The 32-bp space sequence between the centers of UASs C-1 and C-2 is critical for the cooperative multimerization of HbpR.The transcription output from the hbpC promoter is mainly mediated by the proximal UASs C-1/C-2. However, when the UASs C-1/C-2 are deleted, the UASs C-3/C-4 still could compensate the ability of the hbpC promoter to be induced by 2-HBP, albeit at a much lower level. The presence of UAS pair C-3/C-4 mediated a higher promoter activity for transcription of hbpR<a href="#ReferenceHbpR"><sup>[4]</sup></a>.  
 
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=='''Characterization of Biosensor'''==
 
=='''Characterization of Biosensor'''==
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<p><b>Construction and Tuning</b></p>
 
<p><b>Construction and Tuning</b></p>
<p id="ContentHbpR7">
 
We used PCR to get hbpR gene from bacterial strain and inducible promoter Pc' was synthesized by Genscript Company. The gene hbpR was controlled by a constitutive promoter Pc on plasmid pSB4K5. Another plasmid pUC57 containing Pc'-RBS-sfGFP was double transformed with pSB4K5 to construct HbpR biosensor.
 
To tune its performance, Pc constitutive promoter library and RBS library for reporter were constructed.<b>(Fig.4)</b>
 
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<img id="FigurePic5" src=" https://static.igem.org/mediawiki/igem.org/e/ee/HbpR_Figure5_2013Peking_WH.png ", style="width:800px;margin-left:60px"/>
 
<img id="FigurePic5" src=" https://static.igem.org/mediawiki/igem.org/e/ee/HbpR_Figure5_2013Peking_WH.png ", style="width:800px;margin-left:60px"/>
 
<p style="text-align:center">
 
<p style="text-align:center">
<B>Fig.4</B> Construction of the HbpR biosensor and improvements of its performance.</br> (a) Structure of plasmids for hbpR gene and the reporter gene sfGFP. There is a library for the constitutive promoter before HbpR and the RBS before sfGFP respectively, both of which function to fine-tune the expression level of HbpR. (b) Induction ratio of HbpR controlled by promoters with different expression intensity. The effectors 2-HBP and 2-ABP are plotted in different colors. Data were collected via Microplate Reader. (c) Induction ratio of HbpR when exposed to a series of concentration of 2-ABP. The reporter system includes Pc-RBS-sfGFP. Three lines represent sfGFP controlled by different RBS. Fluorescence intensity of sfGFP is detected and calculated to plot induction ratio. (d) Induction ratio of HbpR when exposed to a series of concentration of 2-HBP.  
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<B>Fig.4</B> Construction and optimization of the HbpR biosensor. </br>(<b>a</b>) Schematics for the HbpR biosensor circuit. A library of constitutive promoters preceding the coding sequence of HbpR and a library of RBS sequences preceding sfGFP, respectively were used to fine-tune the HbpR biosensor circuit. (<b>b</b>) Performance of HbpR biosensor using the constitutive promoters of different strength, described with induction ratios. The effectors 2-HBP and 2-ABP are plotted in color intensities. (<b>c</b>) Dose-response curves of HbpR when exposed to gradient concentrations of 2-ABP. Three curves represent different HbpR biosensors where sfGFP are controlled by RBS sequences of different strength. (<b>d</b>) As in (<b>c</b>), dose-response curves of HbpR biosensors when exposed to gradient concentrations of 2-HBP. The induction ratio was calculated by dividing the fluorescence intensity of biosensor exposed to object inducers by the basal fluorescence intensity of the biosensor itself.
 
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<p><b>On-Off Detection</b></p>
 
<p><b>On-Off Detection</b></p>
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<p style="text-align:center">
 
<p style="text-align:center">
<B>Fig.5</B> On-Off test results for sensor strain 114-32 HbpR.</br> (a) On/off response of strain HbpR to 78 aromatic compounds. (For the full name of the compounds, CLICK HERE(hyperlink is needed here)). The strain showed induction ratio more than 10 folds when exposed to 2-HBP and 2-ABP. (b) The detection range of sensor strain HbpR is profiled in yellow at the aromatics spectrum. The structure formula of typical inducer 2-HBP and 2-ABP is showed near its chemical formula.
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<B>Fig.5</B> <a href="http://2013.igem.org/Team:Peking/Team/Notebook/Protocols#Content3">ON/OFF test</a> results for the improved HbpR biosensor.</br>  
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(<b>a</b>) ON-OFF response of HbpR biosensor to overall 78 aromatic compounds. <a href="https://static.igem.org/mediawiki/igem.org/2/24/Peking2013_Chemicals_V3%2B.pdf">Click Here</a> for the full names of aromatic compounds. The biosenor showed induction ratios higher than 10 folds when exposed to 2-HBP and 2-ABP. (<b>b</b>) The detection profile of HbpR biosensor is highlighted in yellow in the aromatics spectrum. The structure formula of typical inducer 2-HBP and 2-ABP is shown.
 
</p>
 
</p>
 
<p><b>Dose-response Curve</b></p>
 
<p><b>Dose-response Curve</b></p>
 
<img id="FigurePic7" src=" https://static.igem.org/mediawiki/igem.org/e/e6/HbpR_Figure7_2013Peking_WH.png ", style="width:400px;margin-left:260px"/>
 
<img id="FigurePic7" src=" https://static.igem.org/mediawiki/igem.org/e/e6/HbpR_Figure7_2013Peking_WH.png ", style="width:400px;margin-left:260px"/>
 
<p style="text-align:center">
 
<p style="text-align:center">
<B>Fig.6</B> Dose response curves for the induction effect of 2-HBP and 2-ABP to the best-performed HbpR sensor strain (J23114-HbpR and Pc-B0032-sfGFP).
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<B>Fig.6</B> Detailed dose-response curves of our best HbpR biosensor (BBa_J23114-HbpR and <i>P<sub>C</sub></i>-BBa_B0032-sfGFP), induced by 2-HBP and 2-ABP, respectively.
 
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== '''Orthogonality''' ==
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== '''Orthogonality of Different Sensor''' ==
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If the presence of an inducer of biosensor A (not an inducer of biosensor B) doesn’t interfere with the dose response of biosensor B to any of its inducers, and vice versa, we call the B and A biosensors are "orthogonal"; namely, no synergistic/antagonistic effects happen between the inducers of A and B biosensors.(for more details, <a href="http://2013.igem.org/Team:Peking/Project/BioSensors/MulticomponentAnalysis">Chick Here</a>)
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we have confirmed the orthogonality among inducers of different biosensors, which is one of the main features we expect for our aromatics-sensing toolkit. Our sensors are well suited to multicomponent analysis.
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<B>Figure.7</B> Summary of the orthogonality assay to evaluate the synergistic/antagonistic effects between the inducers of 4 representative biosensors.</br> No synergistic or antagonistic effects between the inducers of 4 representative biosensors (XylS, NahR, HbpR, and DmpR) were observed. For instance, although the sensing profiles of NahR and XylS overlap to some extent, the NahR-specific and XylS-specific inducers proved to be really orthogonal.
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We have confirmed the orthogonality among inducers of different biosensors, which is one of the main features we expect for our aromatics-sensing toolkit; this allowed the combination of these biosensors to profile aromatics for the ease of practical applications.
 
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Orthoganaility between inducer A (originally detected by biosensor I) and B (originally detected by biosensor II) were tested in the following manner ('''Fig.7'''). To test the effect of inducer B upon the dose-response curve of inducer A obtained by biosensor I:  
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We examined the orthogonality between 4 representative biosensors (<b>Fig.8</b>). The orthogonality test between two biosensors, biosensor I and biosensor II, was performed in the following procedure:
(1) Fluorescence intensity of biosensor I elicited by inducer A of concentration gradient was measured as standard results ('''Fig.7a, Lane 1''');
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</br></br>
 
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1. A typical inducer A for biosensor I and a typical inducer B for biosensor II were selected.<br/>
(2) And fluorescence intensity of biosensor I induced by inducer A of concentration gradient in the presence of a certain concentration of inducer B was measured (<b>Fig.7a, Lane 2 and 3</b>) and compared with the standard results.
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2. The dose response of biosensor I to inducer A was measured, under the perturbation of inducer B.<br/>
 
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3. The dose-response of biosensor II to inducer B was measured, under the perturbation of inducer A.
The effect of inducer A upon the dose-response curve of inducer B obtained by biosensor II was tested vice versa ('''Fig.7b''').
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</br></br>
 
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If biosensor I and biosensor II are orthogonal, the dose response of biosensor I to inducer A should be constant, regardless of the concentrations of inducer B; and the dose response of biosensor II to inducer B should be constant, regardless of the concentrations of inducer A. Namely, for two "orthogonal" biosensors, the perturbation of an unrelated inducer has negligible effect on the dose response of a biosensor to its related inducer (<b>Fig.9</b>).
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<img src="https://static.igem.org/mediawiki/igem.org/4/45/Peking2013_MAFigure1.jpg" style="width:700px;margin-left:110px"  ></a>
 
<img src="https://static.igem.org/mediawiki/igem.org/4/45/Peking2013_MAFigure1.jpg" style="width:700px;margin-left:110px"  ></a>
 
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<html><p style="text-align:center">
 
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<b>Fig.7</b> Orthogonality test assay for inducer A (detected by biosensor I) and inducer B (detected by biosensor II). (a) Biosensor I was added into the test assay. Different mixtures of inducers were added into lane 1, 2, and 3 respectively as listed above. Effect of inducer B upon the dose-response curve of inducer A was tested by comparing the fluorescence intensity of biosensor I among lane 1 ,2, and 3. (b) Biosensor II was added into the test assay. Different mixtures of inducers were added into lane 1, 2, and 3 respectively as listed above. Effect of inducer A upon the dose-response curve of inducer B was tested by comparing the fluorescence intensity of biosensor II among lane 1 ,2, and 3.
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<b>Figure.8</b> Orthogonality test assay for inducer A (detected by biosensor I) and inducer B (detected by biosensor II). (a) Biosensor I was added into the test assay. Different mixtures of inducers were added into lane 1, 2, and 3 respectively as listed above. Effect of inducer B upon the dose-response curve of inducer A was tested by comparing the fluorescence intensity of biosensor I among lane 1 ,2, and 3. (b) Biosensor II was added into the test assay. Different mixtures of inducers were added into lane 1, 2, and 3 respectively as listed above. Effect of inducer A upon the dose-response curve of inducer B was tested by comparing the fluorescence intensity of biosensor II among lane 1 ,2, and 3.
 
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We managed to demonstrate the orthogonality among inducers of different biosensors in a more quantitative and visible way. If inducer A and B were orthogonal, the fluorescence intensity should be identical no matter with or without the irrelevant inducer B. That is to say, the ideal experimental points should be aligned in a line whose slope is one.
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<img src="https://static.igem.org/mediawiki/igem.org/c/c7/Peking2013_Figure3ab.jpg" style="width:800px;margin-left:60px"  ></a>
  
The orithogonality of inducers of XylS, NahR, HbpR and DmpR biosensors have been carefully confirmed using the test assay introduced above ('''Fig.8'''). The experimental points were processed by linear fitting and the slopes of the fitting curves were compared with 1. The closer the slope was to 1, the more orthogonal the inducers were. The results showed that inducers of biosensor XylS and NahR ('''Fig.8a, b'''), XylS and HbpR(''' Fig.8c, d'''), NahR and HbpR ('''Fig.8e, f'''), XylS and DmpR ('''Fig.8g, h'''), NahR and DmpR ('''Fig.8i, j'''), and HbpR and DmpR '''(Fig.8k, l)''' are all highly orthogonal, which is summarized in '''Fig.8'''
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<p style="text-align:center">
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<B>Figure.9 </B>Correlation of the inducer B and the dose-response of biosensor I  to its inducer A.  Each point on the right plot represents a concentration of inducer A. It's x coordinate represents the fluorescence when inducer B is 0 and the y coordinate represents the fluorescence when the cell is exposed to a none-zero concentration of inducer B. If the dose-response of biosensor I is invariant to the concentration of inducer B, the x coordinate of a experimental point should be equal to its y coordinate and the experimental points are supposed to be aligned in a line whose slope is one.
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The orthogonality between XylS, NahR, HbpR and DmpR biosensors have been carefully evaluated using the assay discussed above (<b>Fig.8</b>). The data were processed by linear fitting and the slopes of the fitting curves were compared with 1 (<b>Fig.8, Fig.9</b>). The closer the slope was to 1, the more orthogonal the two biosensors were. Results showed that the biosensor pairs, XylS and NahR (<b>Fig.10a, b</b>), XylS and HbpR (<b>Fig.10c, d</b>), NahR and HbpR (<b>Fig.10e, f</b>), XylS and DmpR (<b>Fig.10g, h</b>), NahR and DmpR (<b>Fig.10i, j</b>), and HbpR and DmpR (<b>Fig.10k, l</b>) are all orthogonal, as summarized in <b>Fig.7</b>.
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<img src="https://static.igem.org/mediawiki/igem.org/4/44/Peking2013_MAFigureef.jpg" style="width:800px;margin-left:60px"  ></a>
 
<img src="https://static.igem.org/mediawiki/igem.org/4/44/Peking2013_MAFigureef.jpg" style="width:800px;margin-left:60px"  ></a>
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<img id="FigurePic6" src=" https://static.igem.org/mediawiki/2013/f/fb/Peking2013_Orthogonality_Fig._4%28g-h%29.png" style="width:800px;margin-left:60px"/>
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<img id="FigurePic7" src=" https://static.igem.org/mediawiki/2013/4/46/Peking2013_Orthogonality_Fig._4%28i-j%29.png" style="width:800px;margin-left:60px"/>
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<img id="FigurePic8" src=" https://static.igem.org/mediawiki/2013/1/15/Peking2013_Orthogonality_Fig._4%28k-l%29.png" style="width:800px;margin-left:60px"/>
 
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<b>Fig.8</b> Experimental points and the linear fitting curves of the orthogonality test. The black dashed lines are with the slopes of 1, showing as the reference line. The slopes of the experimental fitting curves were showed in the upside portion of the figure, all of them were around 1. These data showed the orthogonality among inducers of biosensors(a, b) XylS and NahR; (c, d) XylS and HbpR; (e, f) NahR and HbpR, (g, h) XylS and DmpR, (i, j) NahR and DmpR, and (k, l) HbpR and DmpR. The experimental points and linear fitting curves of biosensor and its inducers are marked in different colors: XylS in red, NahR in green, HbpR in orange and DmpR in dark cyan.
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<B>Figure.10</B> Linear fitting of the data obtained from the orthogonality assay showing that the orthogonality between the 4 representative biosensors. The experiments and data processing were performed as described in <b>Fig. 8</b> and <b>Fig. 9</b>.The black dashed line denotes slope=1 as the reference line. These fittings showed the orthogonality between biosensors, (<b>a, b</b>) XylS and NahR; (<b>c, d</b>) XylS and HbpR; (<b>e, f</b>) NahR and HbpR, (<b>g, h</b>) XylS and DmpR, (<b>i, j</b>) NahR and DmpR, and (<b>k, l</b>) HbpR and DmpR. The experiment data, linear fitting curves of biosensor, and cognate inducers are in different colors: XylS in red, NahR in green, HbpR in orange and DmpR in dark cyan.
 
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== Reference ==
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[1] Jaspers, M. C., Suske, W. A., Schmid, A., Goslings, D. A., Kohler, H. P. E., & van der Meer, J. R. HbpR, a new member of the XylR/DmpR subclass within the NtrC family of bacterial transcriptional activators, regulates expression of 2-hydroxybiphenyl metabolism in Pseudomonas azelaica HBP1. Journal of bacteriology, (2000).182(2), 405-417.
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</br>
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[2] Neuwald AF, Aravind L, Spouge JL, Koonin EV  AAA+: A class of chaperone-like ATPases associated with the assembly, operation, and disassembly of protein complexes. Genome Res (1999)9: 27–43
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[3] Pe´rez-Martı´n J, de Lorenzo. VATP binding to the s54-dependent activator XylR triggers a protein multimerization cycle catalyzed by UAS DNA. Cell (1996) 86: 331–339
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[4] Jaspers, M. C., Sturme, M., & van der Meer, J. R. Unusual location of two nearby pairs of upstream activating sequences for HbpR, the main regulatory protein for the 2-hydroxybiphenyl degradation pathway of ‘Pseudomonas azelaica’HBP1. Microbiology, (2001).147(8), 2183-2194.
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<!-- Uncomment this to enable Functional Parameter display
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===Functional Parameters===
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<partinfo>BBa_K1031911 parameters</partinfo>
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Latest revision as of 04:12, 28 September 2013

HbpR-Terminator

Introduction

HbpR (For more details:http://2013.igem.org/Team:Peking/Project/BioSensors/HbpR) is a 63-kDa prokaryotic transcriptional activators from NtrC family. It shares a highly conserved homology to members of the XylR/DmpR subclass. HbpR was found in Pseudomonas azelaica[1], which can use 2-hydroxybiphenyl (2-HBP) and 2, 2’-dihydroxybiphenyl as sole carbon and energy sources through enzymes encoded by hbpCAD operon in meta-cleavage pathway.

Metabolic Operon

Figure.1 (a) HbpR as the regulator to control the expression of hbp operon. Blue and green rectangles denote hbpCA and hbpD genes controled by PC and PD, respectively. The orange rectangle show the hbpR gene which encodes HbpR protein. When exposed to the effectors, such as 2-hydroxybiphenyl, HbpR will activate transcription at PC and PD. (b) Pathway for the primary metabolism of 2-hydroxybiphenyl and 2-propylphenol in P. azelaica HBP1. The enzymes for each step of the degradation are also indicated.

Protein Domains


Figure.2 Schematics for the domain organization of HbpR protein. N represents the N-terminal of HbpR and C represent the C-terminal. A, B, C and D denote 4 domains of HbpR, respectively, and the numbers below them denote domain boundaries at amino-acid-sequence resolution.C-domain contains an AAA+ ATPase motif[2]. It has the ability to hydrolyze ATP and to interact with σ54 to recruit RNA polymerase for transcription activation. D-domain binds to DNA via a typical helix-turn-helix motif. A-domain is necessary for the recognition of aromatic effector molecules to activate transcription.

Inducible Promoter Structure

Figure.3 The sequences preceding hbpC promoter contains the binding sites for HbpR (UAS,Upstream Activating Sequences[3], boxed in red). Sequence numbers denote the locations of UASs relative to the transcriptional start site of hbpC and hbpD. HbpR binds to UAS C-1 and UAS C-2. The 32-bp space sequence between the centers of UASs C-1 and C-2 is critical for the cooperative multimerization of HbpR.The transcription output from the hbpC promoter is mainly mediated by the proximal UASs C-1/C-2. However, when the UASs C-1/C-2 are deleted, the UASs C-3/C-4 still could compensate the ability of the hbpC promoter to be induced by 2-HBP, albeit at a much lower level. The presence of UAS pair C-3/C-4 mediated a higher promoter activity for transcription of hbpR[4].


Sequence and Features


Assembly Compatibility:
  • 10
    COMPATIBLE WITH RFC[10]
  • 12
    COMPATIBLE WITH RFC[12]
  • 21
    INCOMPATIBLE WITH RFC[21]
    Illegal XhoI site found at 1673
  • 23
    COMPATIBLE WITH RFC[23]
  • 25
    COMPATIBLE WITH RFC[25]
  • 1000
    INCOMPATIBLE WITH RFC[1000]
    Illegal SapI.rc site found at 387

Characterization of Biosensor

Construction and Tuning

Fig.4 Construction and optimization of the HbpR biosensor.
(a) Schematics for the HbpR biosensor circuit. A library of constitutive promoters preceding the coding sequence of HbpR and a library of RBS sequences preceding sfGFP, respectively were used to fine-tune the HbpR biosensor circuit. (b) Performance of HbpR biosensor using the constitutive promoters of different strength, described with induction ratios. The effectors 2-HBP and 2-ABP are plotted in color intensities. (c) Dose-response curves of HbpR when exposed to gradient concentrations of 2-ABP. Three curves represent different HbpR biosensors where sfGFP are controlled by RBS sequences of different strength. (d) As in (c), dose-response curves of HbpR biosensors when exposed to gradient concentrations of 2-HBP. The induction ratio was calculated by dividing the fluorescence intensity of biosensor exposed to object inducers by the basal fluorescence intensity of the biosensor itself.

On-Off Detection

Fig.5 ON/OFF test results for the improved HbpR biosensor.
(a) ON-OFF response of HbpR biosensor to overall 78 aromatic compounds. Click Here for the full names of aromatic compounds. The biosenor showed induction ratios higher than 10 folds when exposed to 2-HBP and 2-ABP. (b) The detection profile of HbpR biosensor is highlighted in yellow in the aromatics spectrum. The structure formula of typical inducer 2-HBP and 2-ABP is shown.

Dose-response Curve

Fig.6 Detailed dose-response curves of our best HbpR biosensor (BBa_J23114-HbpR and PC-BBa_B0032-sfGFP), induced by 2-HBP and 2-ABP, respectively.

Orthogonality of Different Sensor

If the presence of an inducer of biosensor A (not an inducer of biosensor B) doesn’t interfere with the dose response of biosensor B to any of its inducers, and vice versa, we call the B and A biosensors are "orthogonal"; namely, no synergistic/antagonistic effects happen between the inducers of A and B biosensors.(for more details, Chick Here)

SensorHostMain Inducers
XylSPseudomonas putidaBzO 2-MeBzO 3-MeBzO 2,3-MeBzO 3,4-MeBzO
NahRPseudomonas putida4-MeSaA 4-C1SaA 5-C1SaA SaA Aspirin
DmpRPseudomonas sp.600Phl 2-MePhl 3-MePhl 4-MePhl 2-ClPhl
HbpRPseudomonas azelaicao-Phenylphenol 2,6'-DiHydroxybiphenol

Figure.7 Summary of the orthogonality assay to evaluate the synergistic/antagonistic effects between the inducers of 4 representative biosensors.
No synergistic or antagonistic effects between the inducers of 4 representative biosensors (XylS, NahR, HbpR, and DmpR) were observed. For instance, although the sensing profiles of NahR and XylS overlap to some extent, the NahR-specific and XylS-specific inducers proved to be really orthogonal.

We have confirmed the orthogonality among inducers of different biosensors, which is one of the main features we expect for our aromatics-sensing toolkit; this allowed the combination of these biosensors to profile aromatics for the ease of practical applications.

Related Parts:

XylS: https://parts.igem.org/Part:BBa_K1031911 Wiki: http://2013.igem.org/Team:Peking/Project/BioSensors/XylS

NahR: https://parts.igem.org/Part:BBa_K1031610 Wiki: http://2013.igem.org/Team:Peking/Project/BioSensors/NahR

HbpR: https://parts.igem.org/Part:BBa_K1031300 Wiki: http://2013.igem.org/Team:Peking/Project/BioSensors/HbpR

DmpR: http://2013.igem.org/Team:Peking/Project/BioSensors/DmpR


We examined the orthogonality between 4 representative biosensors (Fig.8). The orthogonality test between two biosensors, biosensor I and biosensor II, was performed in the following procedure:

1. A typical inducer A for biosensor I and a typical inducer B for biosensor II were selected.
2. The dose response of biosensor I to inducer A was measured, under the perturbation of inducer B.
3. The dose-response of biosensor II to inducer B was measured, under the perturbation of inducer A.

If biosensor I and biosensor II are orthogonal, the dose response of biosensor I to inducer A should be constant, regardless of the concentrations of inducer B; and the dose response of biosensor II to inducer B should be constant, regardless of the concentrations of inducer A. Namely, for two "orthogonal" biosensors, the perturbation of an unrelated inducer has negligible effect on the dose response of a biosensor to its related inducer (Fig.9).

Figure.8 Orthogonality test assay for inducer A (detected by biosensor I) and inducer B (detected by biosensor II). (a) Biosensor I was added into the test assay. Different mixtures of inducers were added into lane 1, 2, and 3 respectively as listed above. Effect of inducer B upon the dose-response curve of inducer A was tested by comparing the fluorescence intensity of biosensor I among lane 1 ,2, and 3. (b) Biosensor II was added into the test assay. Different mixtures of inducers were added into lane 1, 2, and 3 respectively as listed above. Effect of inducer A upon the dose-response curve of inducer B was tested by comparing the fluorescence intensity of biosensor II among lane 1 ,2, and 3.


Figure.9 Correlation of the inducer B and the dose-response of biosensor I to its inducer A. Each point on the right plot represents a concentration of inducer A. It's x coordinate represents the fluorescence when inducer B is 0 and the y coordinate represents the fluorescence when the cell is exposed to a none-zero concentration of inducer B. If the dose-response of biosensor I is invariant to the concentration of inducer B, the x coordinate of a experimental point should be equal to its y coordinate and the experimental points are supposed to be aligned in a line whose slope is one.


The orthogonality between XylS, NahR, HbpR and DmpR biosensors have been carefully evaluated using the assay discussed above (Fig.8). The data were processed by linear fitting and the slopes of the fitting curves were compared with 1 (Fig.8, Fig.9). The closer the slope was to 1, the more orthogonal the two biosensors were. Results showed that the biosensor pairs, XylS and NahR (Fig.10a, b), XylS and HbpR (Fig.10c, d), NahR and HbpR (Fig.10e, f), XylS and DmpR (Fig.10g, h), NahR and DmpR (Fig.10i, j), and HbpR and DmpR (Fig.10k, l) are all orthogonal, as summarized in Fig.7.

Figure.10 Linear fitting of the data obtained from the orthogonality assay showing that the orthogonality between the 4 representative biosensors. The experiments and data processing were performed as described in Fig. 8 and Fig. 9.The black dashed line denotes slope=1 as the reference line. These fittings showed the orthogonality between biosensors, (a, b) XylS and NahR; (c, d) XylS and HbpR; (e, f) NahR and HbpR, (g, h) XylS and DmpR, (i, j) NahR and DmpR, and (k, l) HbpR and DmpR. The experiment data, linear fitting curves of biosensor, and cognate inducers are in different colors: XylS in red, NahR in green, HbpR in orange and DmpR in dark cyan.

Reference

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