Difference between revisions of "Part:BBa K2150013"

Latest revision as of 00:13, 20 October 2016

A fusion protein combining tetX(BBa_K2150101) with GFP(BBa_E0040)

This protein(refered to as tetX-GFP) combines a tetracycline-degrading enzyme (tetX monooxygenase, BBa_K2150101) and a green fluorescent protein (GFPmt3, BBa_E0040) with a 3*GGGGS linker.

Usage and Biology

TetX-GFP has activities of both tetX and GFP. As a degradation enzyme, it can degrade tetracycline(tc) and its analogs (see BBa_K2150101), and thus gives the tetracycline resistance to E.coli. As a green fluorescent protein, it inherits the normal function of the GFP. However, we noticed that when expressed under the same promoter, the fluorescence intensity(FI) of tetX-GFP was lower than that of GFP at the same growth stage of E.coli. The reason for this may be that the expression level of tetX-GFP is lower than GFP under the same promoter or that tetX-GFP has different excitation spectrum and emission spectrum comparing to GFP.

TetX-GFP can accurately reflect the expression level of tetracycline-degrading enzyeme and report whether our system is working (whether our bacteria are degrading tetracycline). When tetX-GFP is expressed under a tetracycline-regulated promoter such as BBa_R0040, it will become a visible tetracycline sensor in the presence of tetR (BBa_C0040), with no need for additional tetracycline-resistance genes.

Characterization

Role as a degrading enzyme

The E.coli constitutively expressing tetX-GFP (expressed from ptet,BBa_R0040) was able to survive on the LB agar plate with high concentration of tetracycline, while the wild type (DH5alpha) and the E.coli expressing only GFP were not(Fig.1). The E.coli constitutively expressing tetX-GFP had the ability to degrade tetracycline. After 6-hour incubation in M9 containing 100uM tetracycline, the tetracycline, whose concentration was represented by the absorbance at 360nm, was degraded by about 15% (Fig.2).

Role as a green fluorescent enzyme

The FI of E.coli constitutively expressing tetX-GFP increased along with the cell growth. However, at the same OD600, the FI of the tetX-GFP group was lower than that of GFP group (Fig.3).

Sequence and Features