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meffBlue, blue chromoprotein (incl RBS, J23110)

This chromoprotein from the coral Montipora efflorescens, meffBlue (also known as Rtms5), naturally exhibits strong color when expressed. The protein has an absorption maximum at 592 nm giving it a blue color visible to the naked eye. Compared to many other chromoproteins, such as amilCP (BBa_K592009), amilGFP (BBa_K592010), spisPink (BBa_K1033932), asPink (BBa_K1033933) and aeBlue (BBa_K864401), the color development is slower. The color is readily observed in both LB or on agar plates after 24-64 hours of incubation. The protein meffBlue has significant sequence homologies with proteins in the GFP family.

Usage and Biology

This part is useful as a reporter.

Contribution

Group: Linkoping_Sweden iGEM 2021
Author: Ewelina Bladh
Summary: In this contribution, we recorded color development in colonies of E.coli cells of strain XL1. In addition to studying the color development, we determined meffBlue's absorbance maximum wavelength.

Color Development
In order to determine the progression of color development in colonies, E.coli cells (XL1) were plated onto LB-Miller agar plates containing a concentration of 25 ug/mL chloramphenicol. The cells were plated in two ways. The first by plating 100 µL immediately from the liquid culture. The second by first centrifuging the culture, discarding 90% of the supernatant and resuspending the cell pellet in the remaining 10%, followed by plating 100 µL of the resuspension. This results in what is from now on referred to as the diluted and concentrated plate, respectively.

These plates were incubated in 37°C for the following four days, where they were checked upon each day. Figure 1, displayed below, shows the diluted and concentrated plates during this four day study. The illustration of the diluted plate shows that after 12 hours, no color can be seen to the naked eye. This changes over the course of the next 24 hours, where at 36 hours the colonies are clearly visible. The color intensity increases over the next two days. The same can be said about the concentrated plate, but unlike the diluted plate the concentrated plate shows indications of colored colonies already at 12 hours.

Absorbance and Fluorescence
Single colonies displaying a blue color were picked from the diluted plates to create liquid cultures. The liquid cultures consist of 5 mL LB-Miller media and a concentration of 25 µg/mL chloramphenicol. The liquid cultures were incubated at 37°C and 200 rpm for the next two days to ensure protein expression. After incubation, the liquid cultures were centrifuged until a pellet formed. The supernatant was discarded, and the remaining pellet was placed in a -20°C freezer. Cell lysis was done using both water and sonication. The frozen pellet was thawed and 5 mL autoclaved dH2O was added, followed by vortex treatment to resuspend the pellet. Sonication on ice was the next step taken to lyse any cells that did not lyse upon the addition of water. The amplitude of the sonicator was set to 30%, 30 seconds pulsing followed by 30 seconds rest for a total of 2 minutes. Following sonication, the cultures were centrifuged until a pellet formed whereupon the supernatant was transferred to a clean 15 mL Falcon tube and the pellet was discarded. The supernatant of meffBlue can be see to the left in Figure 2. Simultaneous experiments with other chromoproteins was also made, their supernatant can be seen with meffBlue to the right in Figure 2. The following chromoproteins were also assessed in the same way as meffBlue: tsPurple (BBa_K1033903), amajLime (BBa_K1033914), spisPink (BBa_K1033923), gfasPurple (BBa_K1033917), and asPink (BBa_K1033926).

As a control, plates were also made with untransformed XL1-cells. A colony was picked from the diluted plate to start a liquid culture, followed by lysis like the cells transformed with meffBlue. Treatment of control and experimental cells was identical apart from the control culture not being exposed to antibiotics. The supernatant of the control can be seen to the right in Figure 2 along with other chromoproteins.

In order to measure the absorbance, 100 µL supernatant of meffBlue and 100 uL supernatant of the control were pipetted into a 96-well plate and placed in a plate reader. Measurements of absorbance were taken every 2 nm in the range 300 nm to 850 nm. This interval was chosen to include the entire visual spectra including margins. The data yielded from the measurements were subsequently baselined by subtracting the control's absorbance values from meffBlue's absorbance values followed by normalization. The resulting graph for meffBlue's absorbance can be seen in Figure 3 below. In order to be able to compare meffBlue with the other chromoproteins previously mentioned, Figure 4 illustrates normalized absorbance data of all chromoproteins studied. The absorbance maximum of meffBlue proved to occur at approximately 592 nm.

When examining the supernatant extracted from meffBlue-expressing cells on a UV-table, no fluorescence was detected. The chromoprotein amajLime (BBa_K1033914) was studied at the same time, functioning as a positive control. See Figure 5 below which shows meffBlue and the other chromoproteins studied (tspurple, amajLime, spisPink, gfasPurple, and asPink) placed on a UV-table.

Source

Montipora efflorescens. The protein was first extracted and characterized by Beddoe et. al. under the name Rtms5 (UniProtKB/Swiss-Prot: P83690.2). This version is codon optimized for E coli by Genscript.

References

[http://scripts.iucr.org/cgi-bin/paper?cy0089] Beddoe, Travis, et al. "The production, purification and crystallization of a pocilloporin pigment from a reef-forming coral." Acta Crystallographica Section D: Biological Crystallography 59.3 (2003): 597-599.

[http://www.sciencedirect.com/science/article/pii/S0969212603000285] Prescott, Mark, et al. "The 2.2 Å crystal structure of a pocilloporin pigment reveals a nonplanar chromophore conformation." Structure 11.3 (2003): 275-284.

Sequence and Features