NCTU_Formosa 2018 designed a Biobrick contains αS1-casein and a GS linker (BBa_K1974030) ahead as a curcumin bio-sensor.
Team:NCTU Formosa/Wet Lab/Curcumin Biosensor
Figure 1: Composite part of αS1-casein
The goal of our system is to regulate the soil microbiota in order to reach the maximum crop productivity. To accurately predict the curcumin content from NPK content in soil, we create a bio-sensor. This sensor can precisely detect the curcumin containment in turmeric. After the detection of curcumin, results can be fitted into our productivity model and utilize artificial intelligent to increase the accuracy. With the cooperation of productivity model and curcumin transformation model, we can perfectly predict the crop productivity and maintain balance of soil microbiota.
Background Introduction
Curcumin
Curcumin is a natural lipid-soluble yellow compound from the plant turmeric. It is a potent antioxidant as well as anti-tumorigenic and anti- inflammatory molecule. Although curcumin has been proved its therapeutic efficacy against many human ailments, but the problem is it is hard to absorb by human cells. To solve this problem, a paper has discovered a curcumin carrier protein called αS1-casein, shows high binding affinity with curcumin. We then utilize this property of αS1-casein to create a curcumin bio-sensor.
αS1-casein
Caseins are proteins commonly found in mammalian milk and is a mixture of four phosphoprotein. One of the phosphoprotein is αS1-casein, which contains no disulfide bonds and relatively little tertiary structure. As their primary function is nutritional, binding large amounts of calcium, zinc and other biologically important metals, amino acid substitutions or deletions have little impact on function.
The Binding Between Curcumin and αS1-casein
According to the reference, we found how curcumin bind with αS1-casein.Curcumin has a β-diketone moiety, flanked by two phenolic groups, that helps bind to proteins through hydrophobic interactions.The carboxyl-terminal of αS1-casein (100−199 residues) predominantly contains hydrophobic amino acids, which may be involved in the binding process. Residues 14−24 in αS1-casein are hydrophobic in nature and form a surface “patch” of hydrophobicity. Curcumin may probably be binding at these two sites, with two different ranges of affinity through hydrophobic interaction. One with high affinity [(2.01 ± 0.6) × 106 M−1] and the other with low affinity [(6.3 ± 0.4) × 104 M−1].
Establishment
Cloning of αS1-casein
We got the amino acid sequence of αS1-casein from NCBI, and adjust the DNA sequence to optimize its expression in E. coli. We also added a GS linker ahead to enhance the function of sensor and synthesized the gblock fragment from IDT.
First of all of cloning process, we did PCR to acquire the product of GS Linker-αS1 casein DNA fragment. (Fig. 2) Next, we digested the fragment and ligated it to pet30a vector. Finally, we transformed the plasmid with GS Linker-αS1 casein to E. coli. BL21 DE3 and made protein expression.
Figure 2: PCR product of αS1-casein
Chip Production
1. Dip the gold chips in 10mM Mua, RT for 4hrs.
2. Wash the chips with 95% EtOH three times and dry.
3. Add EDC+NHS mixture (100+100mM in DDW) on chips, RT for 1hrs.
4. DDW rinse the chips and dry.
5. Add αS1-casein on chips, RT for 1hrs
6. Wash with PBS three times and dry.
7. Dip the chips in blocking solution, RT for 1.5hrs
8. Wash with PBS three times and dry.
Detection Method
Electrochemistry Introduction
After choosing αS1-casein as our bio-sensor, we used Differential Pulse Voltammetry (DPV) method to detect curcumin containment.
Differential Pulse Voltammetry
DPV uses the difference between before and after the pulse application in order to solve the influence of background noise. Thus, the sensitivity and stability of DPV is better than the common method of cyclic voltammetry, CV. We hope we can use this method to observe the obvious current change when detecting curcumin and create more accurate standard curve in advance.
Measurement protocol of Curcumin bio-sensor
1. Add the diluted curcumin samples on our bio-sensor to react for 30min.
2. Rinse with wash buffer and dry the chips.
3. Wash the reference and counter electrodes with DDW, and dry them.
4. Set up the three electrodes system within electrochemical cell. (Fig. 3, left)
5. Use the prototype of electrochemical machine to measure the DPV method. (Fig.3, right)
Figure 3. Three electrode system (left) and prototype of electrochemical machine (right).
Electrochemical Measurement Result
Pretest of Differential Pulse Voltammetry (DPV)
First of all, we used DPV to check whether our bio-sensor can detect curcumin. As we mentioned above, DPV method tested the current change when curcumin binding. Therefore, we compared the two kinds of chips, the red line was the general chips, and the blue line was the chips modified with αS1-casein (Fig. 4). As long as our bio-sensor contacted with the standard samples of curcumin (from Sigma Aldrich), its current value would become larger. We can easily observed that our bio-sensor with αS1-casein produced more fierce Redox reaction than another. Figure 4 also represented that the bio-sensor modified with αS1-casein have more effect of detecting curcumin than none.
Figure 4. Pretest of curcumin bio-sensor in DPV. (Reduction)
Application - Detection
1. Determine Standard Curve and Create the Formula
We used the standard samples of curcumin and diluted it in dilution buffer. Next, we detected the diluted curcumin samples by curcumin bio-sensor and made the standard curve. Since it was the logarithmic function, we put the curcumin concentration into the natural logarithm, and did the polynomial curve fitting. We obtained the result in Figure 5, R2 =0.9995. This represented the prediction of real samples from the following formula was really close to real value.
Figure 5: The standard curve and the concentration formula of curcumin.
2. The Detection Result of Real Samples from Turmeric Root
Our final goal is to predict the concentration of curcumin in real samples by the bio-sensor. Therefore, we prepared the most curcumin content part, the root of turmeric to pretest our bio-sensor. First of all we milled the turmeric root and divided the powder into two groups. One of them was added with extraction buffer but not underwent the extraction protocol, and the other was added with extraction buffer but underwent the extraction process. The result (Fig. 6) showed only the sample which underwent the extraction process was able to be detected, which represented our sensor had strong specificity to curcumin. Moreover, our curcumin bio-sensor would not be disturbed even if taking the whole turmeric content to detect.
Figure 6: Detection of real samples from turmeric root.
Conclusion
In our conclusion, we use the electrochemistry method, DPV, to prove that we can detect curcumin if we use the gold chips to connect with αS1-casein as bio-sensor. We also make the standard curve and create accurate formula to support the prediction of curcumin concentration in real samples. Finally we certify the specificity is perfect in real samples. According to these experiments, we successfully create a new curcumin bio-sensor. Because of it, we can detect curcumin in time and feedback to our model.
