Difference between revisions of "Part:BBa K346088"

Revision as of 17:14, 19 October 2020

RBS(BBa_B0034)+MerC

This part is constructed for the expression of merC. MerC can transport Hg(II) into the cytosol without the help of merP. For a long time, merC is considered to be of no use in the resistance to Hg(II) because mutations that affect the expression of MerC did not affect the resistance. The discovery in Thipobacillus isolated from mercury mines of operons that apparently had only merC and no merT genes forced reconsideration of the view that merC is vestigal. It has been proposed that merC may be needed under conditions of very high Hg (II) exprosure, perhaps because merC system can uptake (Hg (II) without the need of merP.

We constructed this part to increase the amount of Hg(II) that can be uptaked into the cell. Since the more Hg(II) in the cell, the more merR dimer will bind Hg(II)and be activated. Those active merR dimer will cause the gene expression under pmerT. This part can thus increase the amount of expression of genes under pmerT by increase cellular Hg(II) concentration.

MIT_MAHE 2020

Useage and Biology

The mercury transporter MerC localizes in the inner membrane and has four transmembrane segments which helps in mercuric ion uptake. Unlike MerT which is usually co-expressed with MerP, MerC can help in the Hg2+ uptake alone (Kusano et al. 1990; Inoue et al. 1996; Sahlman et al. 1997, 1999). It has been discovered that E. Coli cells which contain MerC from A. Ferrooxidans is hypersentive to both HgCl2 and CdCl2 suggesting that MerC can recognize and transport Cd2+ and Hg2+ (Sasaki Y. et al. 2005). A study showed that MerC showed greater volatilization than MerF but no increased rate of volatilization in the presence of MerP (Sasaki Y. et al., 2006).

Structure

Hydropathy prediction programs indicated that MerC has four membrane spanning regions with the first region containing two closely spaced cysteine residues and a nearby distal proline residue. The second hydrophobic region has one or more charged residues. As they are found in regions containing positive charge, they are predicted to occur in the cytoplasmic face of the membrane which is close to the carboxyl terminal group of MerC.

Binding to other heavy metals

It has been shown that some heavy metals like cadmium and zinc can activate the expression of Mer operon in some bacteria suggesting that mer genes could be considered putative “sentinal genes” since their expression due to upregulation of the genes in the presence of defined heavy metals. The produced mer proteins might also act as heavy metal chelators. In case of tellurite, even though activation is observed by a synergic effect due to merA and MerC it is not sufficient for resistance. Upregulation of MerC could be associated with facilitating the influx of both toxicants thus favouring rapid detoxification, similar with cadmium in the transgenic merC-expressing S. cerevisiae.

References

1. Inoue C, Kusano T, Silver S (1996) Mercuric ion uptake by Escherichia coli cells producing Thiobacillus ferrooxidans MerC. Biosci Biotech Biochem 60:1289–1292

2. Kusano T, Ji G, Inoue C, Silver S (1990) Constitutive synthesis of a transport function encoded by the Thiobacillus ferrooxidans merC gene cloned in Escherichia coli. J Bacteriol 172:2688–2692

3. Rodríguez-Rojas, F., Díaz-Vásquez, W., Undabarrena, A., Muñoz-Díaz, P., Arenas, F., & Vásquez, C. (2016). Mercury-mediated cross-resistance to tellurite in Pseudomonas spp. isolated from the Chilean Antarctic territory. Metallomics : integrated biometal science, 8(1), 108–117. https://doi.org/10.1039/c5mt00256g

4. Sahlman L, Hagglof EM, Powlowski J (1999) Roles of the four cysteine residues in the function of the integral inner membrane Hg2+-binding protein, MerC. Biochem Biophys Res Commun 255:307–311

5. Sahlman L, Wong W, Powlowski J (1997) A mercuric ion uptake role for the integral inner membrane protein, MerC, involved in bacterial mercuric ion resistance. J Biol Chem 272:29518–29526

6. Sasaki, Y., Hayakawa, T., Inoue, C., Miyazaki, A., Silver, S., & Kusano, T. (2006). Generation of mercury-hyperaccumulating plants through transgenic expression of the bacterial mercury membrane transport protein MerC. Transgenic research, 15(5), 615–625. https://doi.org/10.1007/s11248-006-9008-4

7. Wilson, J. R., Leang, C., Morby, A. P., Hobman, J. L., & Brown, N. L. (2000). MerF is a mercury transport protein: different structures but a common mechanism for mercuric ion transporters?. FEBS letters, 472(1), 78–82. https://doi.org/10.1016/s0014-5793(00)01430-7

Sequence and Features