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Revision as of 15:58, 21 September 2018
Copper Accumulation System
Overview
Since copper is toxic to all types of cells (Ladomersky & Petris, 2015), the presence of transporters for the active and selective uptake of copper ions may initially come as a surprise. But copper also carries out important functions in many cells. As a cofactor for many different enzymes such as superoxide dismutase, it is primarily involved in electron transfer and dioxygen transport and activation (Solomon et al., 2014). Accordingly, there must be natural absorption mechanisms for this trace element into both the periplasm and the cytoplasm. Nevertheless non-bonded, dissolved copper in particular is very toxic, so there are also efficient export systems in E. coli to get rid of excess copper (Rensing & Grass, 2003). In order to create an efficient accumulation system for copper ions, efficient and selective uptake systems must be expressed on the one hand and existing export systems must be suppressed on the other.
Import
In order to increase the concentration of copper ions further, the P-type ATPase HmtA of P. aeruginosa can be used. It actively transports copper ions across the cytoplasmic membrane into the cytoplasm (Lewinsohn, Lee & Rees, 2009). As with the OprC-gene the homologue from the non-pathogenic P. brassicacearum with a protein identity of 80% is used. HmtA expression was found to result in acute hypersensitivity for Cu(II) and Zn(II), which is a result of Cu(II)/Zn(II) uptake, as the expression resulted in increased intracellular concentration of these metal ions (Lewinsohn, Lee & Rees, 2009). Uptake of other cations into the cytoplasm like toxic Ag(I) and Cd(II) ions did not occur (Lewinsohn, Lee & Rees, 2009). As HmtA expression depends on the extracellular Zn(II) concentration and Zn(II) is transported as well as Cu(II) by the HmtA-transporter (Pederick et al., 2015), it can be assumed that HmtA is a zinc importer, which also transports copper ions due to the similarity of size and charge of Zn(II) and Cu(II) ions.
Export
Ladomersky, E., & Petris, M. J. (2015). Copper tolerance and virulence in bacteria. Metallomics, 7(6), 957-964.
Lewinson, O., Lee, A. T., & Rees, D. C. (2009). A P-type ATPase importer that discriminates between essential and toxic transition metals. Proceedings of the National Academy of Sciences, 106(12), 4677-4682.
Pederick, V. G., Eijkelkamp, B. A., Begg, S. L., Ween, M. P., McAllister, L. J., Paton, J. C., & McDevitt, C. A. (2015). ZnuA and zinc homeostasis in Pseudomonas aeruginosa. Scientific reports, 5, 13139.
Postle, K., & Good, R. F. (1983). DNA sequence of the Escherichia coli tonB gene. Proceedings of the National Academy of Sciences, 80(17), 5235-5239.
Rensing, C., & Grass, G. (2003). Escherichia coli mechanisms of copper homeostasis in a changing environment. FEMS microbiology reviews, 27(2-3), 197-213.
Solomon, E. I., Heppner, D. E., Johnston, E. M., Ginsbach, J. W., Cirera, J., Qayyum, M., ... & Tian, L. (2014). Copper active sites in biology. Chemical reviews, 114(7), 3659-3853.
Xiao, M., Zhu, X., Fan, F., Xu, H., Tang, J., Qin, Y., ... & Zhang, X. (2017). Osmotolerance in Escherichia coli is improved by activation of copper efflux genes or supplementation with sulfur containing amino acids. Applied and environmental microbiology, AEM-03050.
Yoneyama, H., & Nakae, T. (1996). Protein C (OprC) of the outer membrane of Pseudomonas aeruginosa is a copper-regulated channel protein. Microbiology, 142(8), 2137-2144.
Lewinson, O., Lee, A. T., & Rees, D. C. (2009). A P-type ATPase importer that discriminates between essential and toxic transition metals. Proceedings of the National Academy of Sciences, 106(12), 4677-4682.
Pederick, V. G., Eijkelkamp, B. A., Begg, S. L., Ween, M. P., McAllister, L. J., Paton, J. C., & McDevitt, C. A. (2015). ZnuA and zinc homeostasis in Pseudomonas aeruginosa. Scientific reports, 5, 13139.
Postle, K., & Good, R. F. (1983). DNA sequence of the Escherichia coli tonB gene. Proceedings of the National Academy of Sciences, 80(17), 5235-5239.
Rensing, C., & Grass, G. (2003). Escherichia coli mechanisms of copper homeostasis in a changing environment. FEMS microbiology reviews, 27(2-3), 197-213.
Solomon, E. I., Heppner, D. E., Johnston, E. M., Ginsbach, J. W., Cirera, J., Qayyum, M., ... & Tian, L. (2014). Copper active sites in biology. Chemical reviews, 114(7), 3659-3853.
Xiao, M., Zhu, X., Fan, F., Xu, H., Tang, J., Qin, Y., ... & Zhang, X. (2017). Osmotolerance in Escherichia coli is improved by activation of copper efflux genes or supplementation with sulfur containing amino acids. Applied and environmental microbiology, AEM-03050.
Yoneyama, H., & Nakae, T. (1996). Protein C (OprC) of the outer membrane of Pseudomonas aeruginosa is a copper-regulated channel protein. Microbiology, 142(8), 2137-2144.