Part:BBa_K3523006

T7 pro-His-katA-His-T7 ter

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  INCOMPATIBLE WITH RFC[21]

  Illegal BamHI site found at 1462
  
• 23
  COMPATIBLE WITH RFC[23]
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal NgoMIV site found at 1334
  
• 1000
  COMPATIBLE WITH RFC[1000]

BBa_K3523006 contains Part:BBa_K3523001, encoding sequence of protein catalase. Its function is to decomposes hydrogen peroxide into water and oxygen; serves to protect cells from the toxic effects of hydrogen peroxide.

Contribution

Our goal of this project is to construct an engineered bacteria which will scavenge superoxide compounds (ROS) in gut quickly and efficiently. To achieve it, we selected a classical enzymes -- catalase(CAT), which are capable of effectively degrading ROS, for overexpression and purification in Escherichia coli BL21 (DE3). By monitoring ROS consumption, the ability of the engineered strain to degrade ROS was verified.

Figure 0

We use T7 promoter to start CAT protein transcription, and T7 terminator to end transcription. At the same time, insert a His protein tag into CAT protein for purification of protein on the nickel column. This part can be used for topics related to the degradation of ROS in the future.

Engineering Success

Characterize the biochemical characteristics of CAT. CAT was expressed in E. coli, bacterial cells were collected and broken, and the CAT enzyme solution was isolated and purified, and further confirmed by the SDS-Page Method (Fig1).

Fig1

                                      Fig. 1 SDS-Page assay the expression of CAT protein

M: Protein Ladder; FT: Flow-through sample; W: Washing sample; 50: Elution sample with 50mM imidazole; 100: Elution sample with 100mM imidazole; 250: Elution sample with 250mM imidazole; 500: Elution sample with 500mM imidazole.

When hydrogen peroxide is relatively abundant, catalase can catalyze hydrogen peroxide to produce water and oxygen. The residual hydrogen peroxide can oxidize the color substrate under the catalysis of Peroxidase to produce the red product (N-(4-antipyryl) -3-chloro-5-sulfonate-Pbenzoquinonemonoimine), and the maximum absorption wavelength is 520nm.We used the hydrogen peroxide standard to make the standard curve (Fig2), so that the amount of residual hydrogen peroxide in the sample could be measured, and the catalase catalyzed the conversion of hydrogen peroxide to water and oxygen in unit volume of unit time could be calculated, thus the enzyme activity of catalase in the sample could be calculated.

Fig2

We added different amounts of enzymes to obtain the maximum rate of CAT catalytic substrates, and we found that the catalytic efficiency of enzymes gradually decreased with the increase of enzyme concentration (Fig3).This indicated that CAT could be well expressed in Escherichia coli, and the purified enzyme also had high catalytic efficiency, which could rapidly transform a large amount of hydrogen peroxide into water and oxygen in a short time.

Fig3

Characterization by 2021iGEM_Shanghai_HS_United

Improvement of an existing part

1.Both of the research focus on promoting the degradation of metabolites in the body by building engineering bacteria.

Compared to the old part BBa_K3523006, they aimed to create an engineered probiotic that can naturally produce SOD in the way of synthetic biology, so as to eliminate the excessive ROS produced by staying up late.

In our project, we put FLR gene into E. coli to produce a strain secreting FLR enzyme. The strain degrades flavonoids to produce DAT and stimulate the immune system to achieve the purposes of anti-inflammatory, antibacterial and anti-cancer. Both of our research objectives are to promote the degradation of metabolites in the body by building engineering bacteria.

2. About plasmid construction, our improvement is reflected in the construction of recombinant plasmids that express different functions using the same promoter-terminator model, composite part T7 pro-tag-Lac ope-XX-T7 ter.

Figure 6. The blast results about the DNA sequence of our new part BBa_K3998005 and the old part BBa_K3523006.

Compared to the old part BBa_K3523006, composite part T7 pro-tag -katA-tag-T7 ter., we design a new part BBa_K3998005 which replaced the katA fragment with the Flr gene fragment. Flr enzyme was successfully produced by transformed Escherichia coli. On the basis of purified recombinant Flr, an excellent Flr activator was obtained. After we obtained the purified protein Flr, namely the FLR enzyme, we conducted enzyme activity tests by using 4 kinds of flavonoids samples: apigenin, chrysin, luteolin, diosmetin with the initial concentration 10mg/L and the concentration of FLR enzyme was 1mM/L. Each sample was guaranteed three replicates of the enzyme activity test in order to gain more data to ensure the credibility of the result of our experiment. All these results indicate that our enzyme has high activity and is capable of degrading multiple flavonoids with a certain universality.

Usage and Biology

In this project, we put the FLR gene into E. coli to produce a strain secreting FLR enzyme efficiently. This strain can better express the FLR gene, improve the degradation of flavonoids, further produce DAT and stimulate the immune system of the human body, so as to achieve anti-inflammatory, antibacterial, anti-cancer and other purposes, at the same time to help reducing clinical treatment costs.

Figure1 Principles of the degradation of intestinal bacteria flavonoids: Flavonoids - > dihydroflavones - > charone - > dihydrocarboncarbonone...

Construct design

Figure 2.The flr protein expression box...

The profiles of every basic part are as follows:

BBa_K4005003

Usage and Biology

It is an polyhistidine tag, which is used in the purification of recombinant proteins

BBa_K4005002

Usage and Biology

It is an transcription terminator derived from the E.coli

Experimental approach

In lab, we successfully constructed the plasmid and it was proved by colony PCR and sequencing result.

Figure3 Flow chart of the engineered strain design ...

Preparation of pET28a vector: The vector was obtained from our plasmid library.

Acquisition of Inserts: Introducing homologous sequences of pET28a vector into 5’-end of Forward (F) & Reverse (R) primer, respectively, aiming to make the ends of amplified inserts and vectors identical to each other.

Table 1.

Recombination: Calculated the amount of DNA for recombination by formula. Diluted pET28a vector and inserts before recombination to make sure the loading accuracy.

Table 2.

Transformation

Place the competent cells on ice (i.e. DH5α competent strain). 2.Pipet 10 μl of the recombination products to 100 μl of the competent cells, flip the tube several times to mix thoroughly (DO NOT VOTEX!), and then place the tube still on ice for 30 min. The volume of transformation products should not be more than 1/6 of the volume of competent cells. 3. Heat-shock the tube at 42℃ for 45 sec and then immediately chill on ice for 2 - 3 min. 4. Add 900 μl of LB medium (without antibiotics) to the tube. Then, shake at 37℃ for 1 hour at 200 - 250 rpm. 5. Preheat the LB plate which contains appropriate selection antibiotic at 37℃ . 6. Centrifuge the culture at 5,000 rpm for 5 min, discard 900 μl of supernatant. Then, re-suspend the pellet with 100 μl of remaining medium and plate it on an agar plate which contains appropriate selection antibiotic. 7. Incubate at 37℃ for 12 -16 hours.

we successfully constructed the plasmid and it was proved by colony PCR and sequencing result.

Proof of function

Enzyme Activity Test of FLR After obtaining the purified protein containing FLR enzyme, we tested its effectiveness in degrading flavonoid.

We conducted enzyme activity tests by using 4 kinds of flavonoid samples: apigenin, chrysin, luteolin, diosmetin with the initial concentration 10mg/L and the concentration of FLR enzyme was 1mM/L. Each sample was guaranteed three replicates of the enzyme activity test in order to to ensure the credibility of the test results. The test results are listed as follows:

Figure 4. Bar graph of the enzyme activity test results.

Results show that the concentration of these 4 flavonoids remarkably decreases after 2 hours which were degraded by the enzyme, even there were only 0.3-5% left after 6 hours. All these results indicate that our enzyme has high activity and is capable of degrading multiple flavonoids with a certain universality.

Bacteria Activity Test

Figure 5. Bar graph of the bacteria activity test results.

All these flavonoids were almost degraded after 2 hours with only 1-7% left, which indicates the strong ability of our engineered E. coli to degrade flavonoids as we expected.

Above all, we could come to the conclusion that the FLR enzyme, as well as the engineered E. coli, is capable of degrading various flavonoids with a certain universality and practicability. In comparison, the degradability of FLR enzyme to these flavonoids could be ranked from greatest to least as apigenin > chrysin > luteolin > diosmetin.

Future Plan

Since the FLR enzyme showed a great ability to decompose flavonoids, we are looking forward to testing how the human body would consume with and without the FLR enzyme. What’s more, if the further experiment succeeds, we will probably try to add the FLR engineered bacteria into yogurt. Yogurt contains a large number of lactic acid bacteria, which themselves belong to acidic substances. After use, they can promote gastrointestinal peristalsis and food digestion. Yogurt helps in digesting food and FLR helps in digesting flavonoids. By adding it, we could make a health-care yogurt which is great for human health improvement.

References

1. Gaohua Yang, Sen Hong, Pengjie Yang, et al. Discovery of an ene-reductase for initiating flavone and flavonol catabolism in gut bacteria, Nature communcations (2021).

2. 黄瑶. 黄酮类物质改善认知功能障碍作用机制的研究进展[J]. 养生大世界 2021年4期, 241-242页, 2021.

3. Thilakarathna S H, Rupasinghe HP. Flavonoids Bioavailability and attempts for bioavailability enhancement[J].Nutrients, 2013, 5(9):3367-3387

4. Ravishankar D, Rajora A K, Greco F, et al. Flavonoids as prospective compounds for anti-cancer therapy[J].Int J Bio- chem Cell Biol, 2013, 45(12):2821-2831