Part:BBa_K5396001
Barbie1_RFP_3xMad10
BARBIE1 is a synthetic protein derived from BaCBM2 through a process of reverse engineering. It has the increased ability to bind to plastics when compared to BaCBM2.
The BARBIE1 protein is fused with the red fluorescent protein (RFP)[ ], which exhibits an excitation maximum at 558 nm and an emission maximum at 583 nm. This fusion enhances the visualization of BARBIE1 by fluorescence-based methods.
This part was used as template to construct BBa_K5396004.
Usage and Biology
Metodo de criação da barbie, importancia da rfp e da tag mad10.
Figure 1. AlphaFold 3 3D simulation of Barbie1 protein with miRFP and three Mad10 tags.
Protein Expression and Purification
The sequence for this part was chemically synthesized by Genscript and arrived pre-cloned in the pET-15b(+) vector. This vector includes a T7 promoter, lacI, a ribosome binding site (RBS), a 6xHis tag, and a T7 terminator. After the arrival, we proceeded with transforming the plasmid into the Escherichia coli BL21(DE3) strain.
Optimization of protein expression
We inoculated E. coli cells expressing Barbie1-RFP-3xMad10 into LB medium with ampicillin, incubating them at 37°C until an OD600 of 0.5 was reached. At this point, 1 mM of IPTG was added to each culture to induce protein expression, and the cultures were left shaking at 37°C for different durations: 3, 4, and 5 hours.
After harvesting the pellets, we extracted the proteins using a protein extraction buffer and sonication, followed by protein quantification using the BSA assay. The samples were then prepared for SDS-PAGE by denaturing them at 95°C and loaded into the gel for electrophoresis.
The electrophoresis results showed a clear and significant difference in protein expression when comparing the IPTG-induced samples (3, 4, and 5 hours) to the control at 0 hours, which had no visible expression bands. However, when comparing the 3, 4, and 5-hour induction times to each other, there was no substantial visual difference in the intensity of the bands, indicating that protein expression was already strong at the 3-hour mark and remained consistent through the later induction times.
Figura X. Analysis of protein expression of Barbie1-RFP-3xMad10 over different induction times (0h, 3h, 4h, 5h) via SDS-PAGE. Lanes: 1- Ladder (molecular weight marker), 2- Barbie1-RFP-3xMad10 (0h), 3- Barbie1-RFP-3xMad10 (3h), 4- Barbie1-RFP-3xMad10 (4h), 5- Barbie1-RFP-3xMad10 (5h), 6- BLS1 (untransformed control).
Final expression and purification
During the sample preparation, we observed a high level of viscosity, which complicated the process. To address this, we centrifuged the sample multiple times and filtered it twice before loading it onto the equipment. Unfortunately, a significant portion of the sample was lost during this additional processing. Despite these challenges, the chromatogram still showed a clear peak corresponding to BARBIE1-RFP-Mad10.
After purification, we sought to understand the cause of the excessive viscosity in our sample. To investigate, we performed a computational analysis using Aggrescan4D (A4D) to predict the aggregation propensities of the protein fold state. The results indicated that BARBIE1-RFP-Mad10 has a higher aggregation propensity compared to BaCBM2.
Based on this finding, we decided to perform new rounds of expression and purification, this time incorporating detergents to improve protein solubilization. In subsequent cycles, we adapted our strategy to account for the aggregation tendency of BARBIE1-RFP-Mad10, aiming to minimize this characteristic and improve the purification process.
Figure X. Chromatogram of BARBIE1-RFP-Mad10 purification using IMAC (Immobilized Metal Affinity Chromatography) on a Ni-column. The peak corresponding to the BARBIE1-RFP-Mad10 protein is highlighted, indicating successful, although partial, purification.
Characterization
SEC-MALS
Circular Dichroism (CD)
CD can provide crucial insights due to the presence of beta sheets in their structures. Typically, β-sheets exhibit a characteristic negative band around 218 nanometers (nm) and a positive band near 195 nm, while α-helices show a negative band around 222 nm and a positive band around 190 nm. However, a limitation of the equipment used restricts the analyzed wavelength range to between 200 and 250 nm.
The pipeline acquisition of the spectrum was followed by a 2 seconds of integration for each point in each 6 spectrum calculated at room temperature (20 ºC). From the collected data, it is calculated its average, subtracted from the water absorbance, normalized, and smoothed using a Savitzky-Golay filter.
Figura ZZ. CD acquisition of Barbie1-RFP-3xMad10 protein at 20 ºC.
Barbie1-RFP-3xMad10 Heating Ramp
An essential evaluation for the protein is the heating ramp, in which we can evaluate how the protein acts in different temperatures and their melting point. For doing so, the same procedure was followed, in which each protein was heated from 20 to 95ºC, as shown in Figure P. The data acquisition was made in steps of 5ºC.
The CD absorbance is shown as the figure’s color map. It is evident that the protein show absorbance in the secondary structure regions, indicating a thermal resistivity.
Figura ZY. Heating ramp for Barbie1-RFP-3xMad10.
Barbie1-RFP-3xMad10 Pontual Spectra
With this result, it is interesting to observe that, even after the protein engineering, the protein could still maintain great results for tests like the described. To further explore it, we also ran a protein pontual spectra, in which we measured CD absorbance for only 215 nanometers, but each measure made at 1ºC increase.
Figure ZZZ shows the result of the experiment, which emphasizes the decrease in the CD absorbance for Barbie1-RFP-3xMad10 as already expected from Figure ZY. Although Barbie1-RFP-3xMad10 loses part of its absorbance with the increase of temperature, it is not possible to confirm its denaturation. A viable hypothesis is some reduction in the beta-sheets structures.
Figure ZY. Pontual spectra for Barbie1-RFP-3xMad10 at 215 nm.
In the first instant, this behavior might show a bad characteristic of Barbie1-RFP-3xMad10. However, the loss of function at high temperatures can be used to properly design the water filter. Once saturated with plastics, the system can be heated to high temperatures making Barbie1-RFP-3xMad10 lose part of its structure. Thus, knowing the function is correlated to the form, the protein might lose its plastic affinity, allowing the removal of microplastics and further processing for reutilizing it.
Heating and Cooling Barbie1-RFP-3xMad10 Ramp
With this possibility in our sights, the following experiment is heating and cooling the protein, in a way we can observe how its structures will behave. Illustrated in Figure XYY, the plot was rotated for better visualizing the CD absorbance in function of temperature variation. From left to right, it is possible to firstly see how Barbie1-RFP-3xMad10behaves when heated and then cooled.
As a result, protein’s CD absorbance in the cooling ramp still presented a signal, indicating it maintained its structure and a consequently renovelation of the possible denoveled parts.
Figure X. Heating and cooling ramp CD absorbance of Barbie1-RFP-3xMad10.
Specific Wavelength Analysis
If we deepen our analysis into 210 and 222 nm, which are in the region of secondary structure absorbance, we can better understand the variancy. In Figure 5, the above graphs are related to the 210 nm wavelength, whereas the graphs from below to the 222 nm.
In a dashed gray line, an average initial absorbance for Barbie1-RFP-3xMad10 was added to highlight the loss of the original absorbance. Additionally, both wavelengths show an interesting behavior, that is an important trend change between 55 and 60 ºC, which may be a critical point for the protein. From the cooling graphs, it is notable how the protein loses part of the original signal, indicating a conformational alteration from the temperature change.
For future adaptation of Barbie1-RFP-3xMad10, it is fundamental to assess and design the protein in a way it can be further reused for multiple filtration.
Figure X. Two specific wavelengths, 210 nm above and the 222 nm below, plots for the heating and cooling ramp for Barbie1-RFP-3xMad10.
Barbie1-RFP-3xMad10 Melting Temperature
From the previous result of analyzing a specific wavelength, it is possible to note the curve’s behavior, which is usual for a protein denaturation. Thus, a viable way to uncover the protein’s melting temperature is by fitting the Boltzmann curve in the collected data, which is given by:
$$A2 + (A1 - A2) / (1 + np.exp((x - x0) / dx)),$$
Where:
- A1 is the protein’s native state;
- A2 is the completely unfolded protein’s state;
- Tm is the protein’s melting temperature;
- k is a constant that represents the curve inclination.
After fitting the curve in Figure 6, the melting point found for Barbie1-RFP-3xMad10 is approximately 58.81ºC. This information is fundamental for building the filter, since it represents stability in a higher temperature. In particular, it is known that in water purifiers the temperatures do not exceed 30 to 35ºC, making the protein appropriate to the system.
Figure 6. Boltzmann fit in the absorbance values of Barbie1-RFP-3xMad10 in a heating ramp.
Plastic Interaction Analysis
Through secondary structures absorbance, it was possible to observe that Barbie1-RFP-3xMad10 structure do not change in the presence of plastic nanoparticles
Finally, the last experimental evaluation at CD was with the polystyrene nanoplastics. We used a 100 nanometer particle which was inserted into a solution with Barbie1-RFP-3xMad10.
Nevertheless, as reported from the computational simulations, we do not expect any conformational change. Since CD is only evaluating the absorbance in secondary structures, there may not happen major differences in the experiment.
Consequently, Figure WWW shows as projected. When the Barbie1-RFP-3xMad10a spectra is plotted with the nanoparticle solution spectra, minor changes can be observed. Specifically, this contrast might be a result of the polystyrene nanoparticle scattering, creating noise in the measurement.
Considering we were not able to assess the plastic-protein binding, further studies might be done. One important form to evaluate this is the infrared spectroscopy, which allows studying the vibrational frequencies of molecules.
Sequence and Features
- 10COMPATIBLE WITH RFC[10]
- 12COMPATIBLE WITH RFC[12]
- 21INCOMPATIBLE WITH RFC[21]Illegal BglII site found at 594
- 23COMPATIBLE WITH RFC[23]
- 25INCOMPATIBLE WITH RFC[25]Illegal AgeI site found at 88
- 1000COMPATIBLE WITH RFC[1000]
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