Difference between revisions of "Part:BBa K346005"

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Mercury (II) ions absorption device

Hg(II) Bioabsorption Device

Dsba-mbp(mercury metal binding peptide)+mbp(mercury metal binding peptide)+lpp-ompa-mbp(mercury metal binding peptide)

This composite part belongs to the mercury bioabsorption device constructed by Peking University 2010 iGEM team

Description:

As the main part of mercury bioabsorbant of our project, this device is designed to combine three subparts----the T7promoter-rbs-Dsba-mbp-terminator, T7promoter-rbs-mbp-terminator and T7promoter-rbs-lpp-ompa-mbp-terminator (figure1), which can bind mercury separately in periplasm, cytosol and the membrane of E.coli, to make full use of the space and maximize the absorption of mercury. Since all these subparts are driven by their own T7promotor, they can be expressed when T7polymerase exists. 1 Metal binding pepside(MBP) MBP was designed as a single polypeptide that could fold into an antiparallel coiled coil, just like MerR, the mercury-responsive metalloregulatory protein MerR dose. As a result, the engineered MBP has a similar mercury binding capacity as MerR. We got the the gene of mbp by PCR with the plasmid from Anna. 2 Dsba-mbp Dsba-mbp is a fusion protein aiming to transport the MBP protein to the periplasm. Dsba is a signal peptide, which can be recognized and transported to the periplasm. 3 Lpp-ompa-mbp Lpp-ompa-mbp is designed as a fusion protein consisting of the signal sequence and first 9 amino acid of Lpp, residue 46~159 of OmpA and the metal binding peptide(MBP). The signal peptide of the N-termini of this fusion protein targets the protein on the membrane while the trans-membrane domain of Ompa serves as an anchor. MBP is on the externally exposed loops of OmpA, which can be anchored to the outer membrane.

Experiment:

The three subparts are ligated together step by step with sub-clone. To test the function of the device, both expression experiment and function test is necessary. As a result, we have test the size of the expressed proteins with SDS-page and Western blot. Besides, to test the efficiency of mercury binding, we also carried out the function test with ICP-AES, which can test the quantity of mercury binding by the bacteria with the device.

Results:

Expression of proteins The Dsba-mbp, mbp and lpp-ompa-mbp are inserted into the commercial plasmid PET21A. Then the plasmid is transferred to E.coli strain BL21, which can generate T7polyerase when induced with IPTG. Both induced cells and uninduced cells(as control) are centrifuged to get the cytosol, the periplasm and the membrane separated. The SDS-page and Western blot of the expressed proteins in these three parts(figure2) show that induced cells expressed an identical IPTG-inducible protein at the proper place with the size of ~12kD for MBP, ~40kD for Dsba-MBP and ~27kD for LPP-OMPA-MBP, all of which are consist with the predicted size, indicating that all these three coding sequence can be expressed normally in the right place. File:Mercury device figure2 Function test Having made sure that the protein can express normally in the proper place, the function tests experiment are carried out with ICP-AES. To test the efficiency of mercury absorption of our mercury bioabsorption device in different concentration of mercury, the concentration gradient is set from 10^-7M to 10^-5M, the results are shown in figure 3. In addition, compare the capacity of metal binding of the device which contains three subparts with the subparts alone(MBP, Dsba-MBP and LPP-OMPA-MBP), these four parts are tested in the mercury concentration of 10^-5M to compare with each other, with the results shown in figure 4. File:Mercury figure3