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Methylmercury Transport system design-1

Circuit

Constitutive Promoter – RBS – MerR - PmerT promoter – RBS - MerP – RBS – MerT – RBS – MerE – RBS - MerC – RBS – GFP - Double Terminator

Usage and Biology

MerP is the periplasmic component of the Mer transport system which helps in the uptake of mercury inside the cell. It binds to a single Hg (II) ion using its two conserved cysteine residues, which define its metal-binding motif. It removes any attached ligands before passing the Hg (II) on to MerT transmembrane protein. It is the most abundantly synthesized protein in the mer operon due to its role in scavenging of Hg (II) in the periplasm (Steele, R. A., & Opella, S. J.1997). MerT is a transmembrane protein which receives mercury from MerP at its first transmembrane helix and transports it into the cytoplasm of the bacterial cell (T. Barkay et al., 2003). MerE is a transmembrane component of the mer transport system which helps in the uptake of mercury inside the cell. It helps in the transport of organo-mercury compounds. MerC is a transmembrane component of the mer transport system which helps in the uptake of mercury inside the cell. It can function without the help of MerP and has been hypothesized to be required in cases of high mercury concentration (Sone et al., 2013).

Proposed experimentation

To determine the final transport design, the team has proposed three circuits consisting of a combination of genes among MerP, MerC, MerT and MerE. The circuit showing the most effective results can be chosen as the bio-brick for the transport system for our first plasmid. Circuits we have proposed to test for the final transport design system: MerP-MerT-MerC-MerE, MerC-MerE, MerP-MerT –MerE. To test the efficiency and characterize each of the 4 parts separately we carry out experiments with each of the parts making use of 2 test circuits and 2 controls. Circuits: The final transport design system, Constitutive Promoter- RBS – (The part to be tested, i.e. MerP, MerC, MerT or MerE) -RBS-Double Terminator. Controls: Final circuit design without the part to be tested, Wild type Escherichia coli DH5alpha. E. coli cells inoculated with methylmercury chloride must be grown for the required amount of time according to the results of the preliminary experiment respectively for the 2 circuits to be tested and 2 controls. The cell suspension must be centrifuged and the mercury concentration in the supernatant for each set must be determined with gas chromatography. Plots of concentration vs time for each of the sets should be analysed to understand the efficiency of the parts in transporting methylmercury.

Expected result: The most efficient transport system is the final transport circuit design. Also, the team expects to see that MerC contributes significantly in the presence of other transport system elements. It shows that MerC is the most efficient tool as it is sufficient for mercurial transport into cells. The team also expects to see that MerE contributes significantly in the presence of other transport system elements but less efficient than MerT in presence of other transport system elements. What is unexpected is if there are two transport system circuits with similar efficiency, then one with the least genetic burden must be selected. The expected result must show the efficiency of MerP, MerT, MerE, MerC all together in transporting methylmercury, which should be higher than the natural transport (without mer operon transporters).

Sequence and features

References

Barkay, T., Miller, S. M., & Summers, A. O. (2003). Bacterial mercury resistance from atoms to ecosystems. FEMS Microbiology Reviews, 27(2–3), 355–384. https://doi.org/10.1016/S0168-6445(03)00046-9

Rossy, E., Sénèque, O., Lascoux, D., Lemaire, D., Crouzy, S., Delangle, P., & Covès, J. (2004). Is the cytoplasmic loop of MerT, the mercuric ion transport protein, involved in mercury transfer to the mercuric reductase? FEBS Letters, 575(1–3), 86–90. https://doi.org/10.1016/j.febslet.2004.08.041

Sone, Y., Nakamura, R., Pan-Hou, H., Itoh, T., & Kiyono, M. (2013). Role of MerC, MerE, MerF, MerT, and/or MerP in resistance to mercurials and the transport of mercurials in escherichia coli. Biological and Pharmaceutical Bulletin, 36(11), 1835–1841. https://doi.org/10.1248/bpb.b13-00554

Steele, R. A., & Opella, S. J. (1997). Structures of the reduced and mercury- bound forms of merP, the periplasmic protein from the bacterial mercury detoxification system. Biochemistry, 36(23), 6885–6895. https://doi.org/10.1021/bi9631632