Part:BBa_K1668008
tcdA1-device
the part tcdA1 device is composed of arabinose inducible promoter pBad BBa_I0500, toxin protein tcdA1 coding sequnceBBa_K1668008 and composite part mCherry BBa_K1668011.
We use the device to tandem express toxic protein tcdA1 and mCherry. Toxic protein tcdA1 is a macro channel forming toxin used for termite control in our project and mCherry is a reporter.
Sequence and Features
- 10COMPATIBLE WITH RFC[10]
- 12INCOMPATIBLE WITH RFC[12]Illegal NheI site found at 1205
Illegal NheI site found at 8257
Illegal NheI site found at 8590 - 21INCOMPATIBLE WITH RFC[21]Illegal BglII site found at 1651
Illegal BamHI site found at 1144 - 23COMPATIBLE WITH RFC[23]
- 25INCOMPATIBLE WITH RFC[25]Illegal NgoMIV site found at 7691
Illegal NgoMIV site found at 8351
Illegal AgeI site found at 979
Illegal AgeI site found at 3527 - 1000INCOMPATIBLE WITH RFC[1000]Illegal SapI site found at 961
Characterization
OVERVIEW
We construct the device tcdA1 to tandem express toxic protein tcdA1 and reporter mCherry. Toxic protein tcdA1 is used to kill termites in our project.
tcdA1, one of the biggest proteins in bacteria (285kDa), is first found in Photorhabdus luminescens. It forms channels and assists other toxins across the cell membrane(1). It belongs to tc toxic protein family, which is widely distributed among different gram-negative and gram-positive bacteria.
We clone and standardize the gene into standard plasmid pSB1C3. After confirmation of digestion and sequencing, we transform the plasmid into E.coli BL21(DE3) to achieve better expression level. Despite we observe that transformants have obviously turned red, we didn’t figure out the expected protein band in SDS-PAGE. Judging that the protein is considerably huge in bacteria, more improvements are needed.
BACKGROUND
tcdA1 is a pore-forming macro-protein, which can keep the ability to form a pore in a large pH range (from 4 to 11). To be noticed, at pH11, the pore-forming activity of tcdA1 is more than 100-fold greater than at pH6. As the midguts of most insects are alkaline, tc toxic proteins are effective by feeding on insects, including termites.
In 2013, the structure of tcdA1 was revealed by researchers and reported in nature(1). As displayed in figure1a&b, the tcdA1 is composed of three parts: N-terminal a-helical domain(brown), the central b-sheet domain(green) and the C-terminal pore-forming domain(yellow). The protein has two states: pre-pore state and pore state. The pore-forming domain (figure 1c) sticks out to form pore, changing into pore state (figure 2).
Moreover, the tcdA1 toxin helps other toxins to enter the cell membrane. Naturally in strain TT01, tcdA1 is expressed homologously with other toxins, for example, tcdB1 and tcc toxins. TcdA1 helps to transfer the latter into the cell to maximum the toxic effect(figure 3).
RESULTS
PLASMID CONSTRUCTION
5μl samples of the double enzyme digestion products for tcdA1-device were loaded onto a 1% BioRad Ready Agarose Mini Gel, then subjected to AGE. See (protocol) for AGE parameters. Sizes of the XbaI and PstI–cleaved assemblies were determined by AGE analysis. The DNA size standards were the DL5,000 DNA Marker (M2; TaKaRa, Cat#3428A) and 1kb DNA Ladder (Dye Plus)(M2; TaKaRa, Cat#3426A). Bands were visualized with a Shanghai Peiqing JS-380A Fluorescence Imager.
First we construct the tcdA1 device in pSB1A2. Our target fragments can be clearly seen in the right position (figure 4). As the fragment is a little big(7.2k), the efficiency is low when we change the backbone to pSB1C3 and the unwanted fragment is hard to explain(figure 5).
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