Part:BBa_K1189018
Human ferritin di-subunit with E coil w/ LacI promoter
This part was created by fusing the heavy chain and light chains (BBa_K1189024 BBa_K1189025) of human ferritin together (sequences from: P02794 and P02792 [UniParc]). It is expressed under the lacI promoter (BBa_J04500) and has a his-tag for protein purification. An E-coil (BBa_K1189011) is included in order to allow binding of parts containing the respective K-coil (BBa_K1189010). Characterization of this part was done primarily with commercially purchased ferritin, which is structurally very similar to this recombinant ferritin (Figure 1).
This construct can be used as a reporter through a modification of the iron core to form Prussian Blue (Figure 2). The resulting molecule can then catalyze the formation of radicals from hydrogen peroxide, which can then cause a colour change in substrates such as TMB or ABTS (Figure 3) (Zhang et al., 2013).
This protein is a highly robust protein, remaining stable under extreme pH, temperature, and denaturing conditions. It is also highly accepting of fusion proteins, as it continues to form the nanoparticle despite fusions to both N-terminus and C-terminus. In addition, proteins fused to this protein have been found to be stabilized due to the fusion.
Figure 1. Ribbon visualization of a fully assembled ferritin protein. Figure 2. Image of the colours of ABTS and TMB (10 mg/mL for both) after reacting with Prussian blue ferritin. Figure 3. Comparison image of commercial ferritin to Prussian blue ferritin after the synthesis reaction. The synthesis reaction took place over a 12 hour time period.
Applications of BBa_K1189018
The main purpose of this page is to display the characterization data of Prussian blue chemically modified commercial horse spleen ferritin as a catalyst. This ferritin is extremely similar to our constructed ferritin and we do not anticipate any differences in their properties. Next we show how our own constructed ferritin displays the same catalytic activity. At the end we show how the coil found in this part can bind to coils found on our other parts.
Kinetic Analysis of Prussian Blue Ferritin
We performed a kinetic analysis of our Prussian blue ferritin. We included a comparison of Prussian blue horse spleen ferritin to regular horse spleen ferritin for both TMB and ABTS (Figures 1 and 2). For both of the substrates we can see that normal ferritin has a very low catalytic activity compared to our modified ferritin. Using this data were able to determine the Michaelis-Menten catalytic constants for Prussian blue ferritin with different substrates.
Figure 1. Measurements of the absorbance of the 650nm light by the substrate TMB over a period of 600 seconds. 6 µL of 10 mg/mL substrate was used in a 242 µL reaction volume.Commercial Prussian blue ferritin ( 10 µL of 0.022 mg/mL sample) is represented by the blue data points. Orange data points are a negative control using standard ferritin (10 µL of 0.047 mg/mL sample). Negative controls are TMB and hydrogen peroxide, and TMB only. Standard error of the mean bars are based on a sample size where n=8. Substrate and hydrogen peroxide sample data is not clearly visible as it is in line with the substrate only data.
Figure 2. Measurements of the absorbance of the 415nm light by the substrate ABTS over a period of 600 seconds. 8 µL of 10 mg/mL substrate was used in a 242 µL reaction volume. Commercial Prussian blue ferritin ( 10 µL of 0.022 mg/mL sample) is represented by the blue data points. Orange data points are a negative control using standard ferritin (10 µL of 0.047 mg/mL sample). Negative controls are ABTS and hydrogen peroxide, and ABTS only. Standard error of the mean bars are based on a sample size where n=8.
In order to complete our kinetic analysis we had to determine the catalytic properties of our Prussian blue ferritin according to the Michaelis-Menten kinetic model. For these tests we varied the colourimetric substrate concentrations (ABTS and TMB) (Figures 3 and 4). We also varied the hydrogen peroxide concentration in association with TMB as this the first chemical compound that will react in the system (Figure 5).
Figure 3. Michaelis-Menten kinetic plot for commercial Prussian blue ferritin based on varying concentrations of ABTS. Absorbance readings were taken at 415 nm. Velocities were generated from the average slope of eight data sets. Standard error of the mean bars are not displayed but are present in the foundational data (eg. Figure 6).
Figure 4. Michaelis-Menten kinetic plot for commercial Prussian blue ferritin based on varying concentrations of TMB. Absorbance readings were taken at 650 nm. Velocities were generated from the average slope of eight data sets. Standard error of the mean bars are not displayed but are present in the foundational data (eg. Figure 5).
Figure 5. Michaelis-Menten kinetic plot for commercial Prussian blue ferritin based on varying concentrations of hydrogen peroxide. Absorbance readings were taken at 650 nm which measure the breakdown of TMB. Velocities were generated from the average slope of eight data sets. Standard error of the mean bars are not displayed but are present in the foundational data.
| Catalyst | Enzyme Concentration (M) | Substrate | Km (mM) | Vmax (Ms-1) | Kcat (s-1) | Kcat/Km (M-1s-1) |
| Prussian Blue Ferritin | 1.31 x 10-9 | ABTS | 0.448 | 1.25 x 10-8 | 9.51 | 2.12 x 104 |
| Prussian Blue Ferritin | 1.31 x 10-9 | TMB | 0.0432 | 1.12 x 10-7 | 85.3 | 1.97 x 106 |
| Prussian Blue Ferritin | 1.44 x 10-9 | H2O2 (TMB) | 0.0176 | 1.45 x 10-8 | 10.1 | 5.71 x 105 |
We also performed a pH optimization of our Prussian blue ferritin using the substrates TMB and ABTS (Figure 6 and 7). The results show TMB to be a much more robust substrate, showing high catalytic activity across a more broad range of pH compared to ABTS.
Figure 6. pH optimization of commercial Prussian blue ferritin with ABTS. Data is presented as a relative activity based on the highest activity seen during the experiment. Absorbance readings were taken at 415 nm to detect the colourimetric change in a 242 µL solution. Data based on a sample size of n=8. Standard error of the mean bars are not displayed due to their lack of visibility.
Figure 7. pH optimization of commercial Prussian blue ferritin with TMB. Data is presented as a relative activity based on the highest activity seen during the experiment. Absorbance readings were taken at 650 nm to detect the colourimetric change in a 242 µL solution. Data based on a sample size of n=8. Standard error of the mean bars are not displayed due to their lack of visibility.
Another aspect of our analysis was determining the optimal temperature for catalytic activity of Prussian blue ferritin (Figure 8 and 9). This showed us that the Prussian blue reporter has a much higher catalytic activity at higher temperatures.
Figure 8. Temperature optimization of commercial Prussian blue ferritin with ABTS. Data is presented as a relative activity based on the highest activity seen during the experiment. Absorbance readings were taken at 415 nm to detect the colourimetric change in a 242 µL solution. Data based on a sample size of n=8. Standard error of the mean bars are not displayed due to their lack of visibility.
Figure 9. Temperature optimization of commerical Prussian blue ferritin with TMB. Data is presented as a relative activity based on the highest activity seen during the experiment. Absorbance readings were taken at 650 nm to detect the colourimetric change in a 242 µL solution. Data based on a sample size of n=8. Standard error of the mean bars are not displayed due to their lack of visibility.
The next aspect of our analysis was to see how Prussian blue ferritin would act in a catalytic sense on nitrocellulose (Figures 10 and 11). From these results we can that TMB is a better substrate on for use on nitrocellulose(Figure 11). With this substrate we saw a result from only 5 ng of Prussian blue ferritin present on the nitrocellulose.
Figure 10. Blots of Prussian blue ferritin on nitrocellulose (5 µL samples) that are reacted with ABTS (10 mg/mL). Concentrations of Prussian blue ferritin used are indicated in the figure. Results indicate colour change after 6 minutes. Controls include the substrate by itself, unmodified ferritin and bovine serum albumin. Four replicates are present per sample trial.
Figure 11. Blots of Prussian blue ferritin on nitrocellulose (5 µL samples) that are reacted with TMB (10 mg/mL). Concentrations of Prussian blue ferritin used are indicated in the figure. Results indicate colour change after 6 minutes. Controls include the substrate by itself, unmodified ferritin and bovine serum albumin. Four replicates are present per sample trial.
We applied a scaled down Prussian blue synthesis experiment to our own ferritinOur own Prussian blue ferritin was then exposed to the TMB substrate (Figure 12). From the results we can see that the ferritin with the E-coil attached had excellent catalytic activity.
Figure 12. Measurements of the coloured substrate TMB (10 mg/mL) at 650 nm over a 600 second time period for our own Prussian blue ferritin and unmodified ferritin. Sample volume was 242 µL. Controls for this experiment include bovine serum albumin (1 mg/mL)and the substrate solution by itself. Due to limitations on the protein available only one replicate was performed. Zero time points do not have low absorbance as colour change was rapid and began before measurements started.
After successfully confirming that we could convert our own ferritin proteins that were produced from the parts we constructed (BBa_K1189018, BBa_K1189021) into Prussian blue ferritin the next step was to evaluate how the design of our parts could potentially affect the reporter activity of our Prussian blue ferritin. Based on the spatial modelling performed by our team it was suggested that assembly of the ferritin nanoparticle with TALE proteins directly fused was highly unlikely. This is because the TALE proteins are significantly larger than the ferritin subunits. Their size would likely result in steric hindrance and prevent the assembly of the full ferritin protein. In order to test the predictions put forward by our modelling we ensured that our protein samples were balanced in order to have the same number ferritin cores in each sample. The catalytic activity of these proteins was then compared. From the data gathered we saw that the Prussian blue ferritin with fused coils (even if TALES are additionally bound to the ferritin via coils) was more effective as a reporter than having the TALE proteins directly fused to the ferritin nanoparticle (Figure 13). The results from this experiment suggest that the predictions made by our model were correct. Using coils however alleviates this issue as these coils are small and would not interfere in the ferritin self-assembly but can be used to attach our TALES to create the FerriTALE.
Figure 12. Samples of our parts that were converted to Prussian Blue ferritin were mole balanced in order to ensure that the same number of effective ferritin cores are present in every sample. Additionally the ferritin-coil fusion was incubated with the TALE-coil fusion part in order to allow their binding for a separate trial. Negative controls include unconverted recombinant ferritin, bovine serum albumin and a substrate only control. Samples were incubated with a TMB substrate solution for 10 minutes at a pH of 5.6. Absorbance readings were taken at the 10 minute time-point at a wavelength of 650 nm. An ANOVA (analysis of variants) was performed upon the values to determine that there was statistical difference in the data gathered (based off of three replicates). A t-test was then performed which determined that the * columns are significantly different from the ** column (p=0.0012). Neither * column is significantly different from each other (p=0.67).
Sequence and Features
- 10COMPATIBLE WITH RFC[10]
- 12COMPATIBLE WITH RFC[12]
- 21COMPATIBLE WITH RFC[21]
- 23COMPATIBLE WITH RFC[23]
- 25COMPATIBLE WITH RFC[25]
- 1000INCOMPATIBLE WITH RFC[1000]Illegal BsaI.rc site found at 1289
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