Revision as of 14:34, 15 October 2018

superfolder GFP measurement device

It is a measurement device for superfolder GFP (BBa_I746916) fluorescence intensity, which is composed of Anderson promoter (BBa_J23104), RBS (BBa_B0034), superfolder GFP (BBa_I746916) and double terminator (BBa_B0010 and BBa_B0012).

1. Usage and Biology

Green fluorescent protein (GFP) exhibits intrinsic fluorescence and is commonly used as a reporter gene in intact cells and organisms [1]. Many mutants of the protein with either modified spectral properties, increased fluorescence intensity, or improved folding properties have been reported [2].

GFP often misfolds when expressed as fusions with other proteins, while a robustly folded version of GFP, called superfolder GFP (sfGFP), was developed and described by Pédelacq et al at 2006[3] that folds well even when fused to poorly folded polypeptides. We decided to use sfGFP as our reporter protein due to its faster folded feature and higher fluorescence intensity. The superfolder GFP had been registered in iGEM BBa_I746916. However, the superfolder GFP (BBa_I746916) contains a BbsI restriction site, and the BbsI restriction endonuclease is an economical and efficient enzyme used in Golden Gate assembly, so the superfolder GFP (BBa_I746916) cannot be used for Golden Gate assembly.

So, this year our team improved the superfolder GFP (BBa_I746916). Firstly, we registered the superfolder GFP designed by Overkamp W et al[4] with a BBa_K2541400 (called sfGFP_optimism). It is a codon optimized sfGFP. Secondly, we made two point mutations in superfolder GFP (BBa_I746916) to eliminate its BbsI restriction site without changing its amino acid sequence. We made it from 5’-gaagac-3’ to 5’-gaggat-3’. We called the mutated variant sfGFP(BbsI free) (BBa_K2541401). The two sfGFP we designed don't have BbsI restriction site, so they can be used in Golden Gate assembly.

In order to compare the two sfGFP we designed with superfolder GFP (BBa_I746916), we designed this measurement device to measure superfolder GFP (BBa_I746916) fluorescence intensity.

2. Characterization

We got the emission and excitation spectra of the three sfGFP: sfGFP_optimism (BBa_K2541400), sfGFP(BbsI free) (BBa_K2541401) and superfolder GFP (BBa_I746916) (figure 2).

Figure 1.

We detected the expression intensity of the three sfGFP. According to the results (figure 3), we found out that the fluorescence intensity of sfGFP_optimism (BBa_K2541400) and sfGFP(BbsI free) (BBa_K2541401) are higher than superfolder GFP (BBa_I746916).

Figure 2. The expression of three types of sfGFP in E.coli. The grey line represents fluorescent expression of sfGFP_optimism (BBa_K2541400), the orange line represents fluorescent expression of sfGFP(BbsI free) (BBa_K2541401), the blue line represents fluorescent expression of superfolder GFP (BBa_I746916) and the yellow line represents fluorescent expression of negtive control (BBa_J364007).

3. Conclusion

We have made an improvement on the superfolder GFP (BBa_I746916). Our sfGFP_optimism (BBa_K2541400) and sfGFP(BbsI free) (BBa_K2541401) are BbsI restriction site free, which can be used in Golden Gate assembly to achieve efficient and rapid assembly of gene fragments. And their fluorescence intensity are higher than superfolder GFP (BBa_I746916).

Sequence and Features