Improvement of Liu iGEM 2017s part BBa_K2474000

With the use of site-direted mutagenesis the goal was to improve the part of last years LiU iGEM team biobrick BBa_K2474000. This was done by removing the amyloid-beta 1-42 via a restiction site and removing unnecessary bases as shown in figure 1. By doing this the fluorescent protein mNeonGreen (mNG) can be used as a reporter gene with a different protein from amyloid-beta 1-42. The promoter of this system is AraC/pBAD system.

The two additions was made with site-directed mutagenesis. Firstly the stop codon was added and sequenced, which was later used as the new template for the mutation to add the SpeI site. As seen in figure 1, we used SpeI to cleave off the unnecessary bases from the plasmid, and later ligated it back together without the amyloid-beta 1-42 fragment.

Figure 1. A illutration of the steps made.

Results

The results for our improved part can be seen in below. The reason we choose to improve this part was not only to create a functional reporter system, but also to illustrate the loss of exchange with a aggregation prone fusion tag. From fig 2. you can clearly see that the version without amyloid-beta 1-42 folds better and thus gives a much higher fluorescence, while the fusion version is having trouble. The two parts was grown in LB-medium, 0.25 mg/ml L-arabinose and 25 ug/ml chloramphenicol over 16 hours. They were then lysed through the "freeze-thaw" method and centrifuged. The supernatant was saved and placed on an UV table as seen in fig 2.

Figure 2. From left to right: Reference with only water, BBa_K2671000 (mutated part) and BBa_K2474000.

Sequencing

Seen below in fig 3. is the chromatograms from sequencing. The results shows that the mutation GCC --> TTA was successful. The length of the sequence also suggest that amyloid-beta 1-42 was removed. Both parts was sequenced using the VR primer, and ~170 bases shorter fits completely with the length of the removed fragment. The full sequencing files including chromatograms can be found at BBa_K2671000.

Figure 3. The chromatograms from sequencing. Left is BBa_K2671000 (mutated part) and right is BBa_K2474000 (template).