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Domain 3:

Metabolism

Copper Homeostasis in and Other

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  • Authors: Christopher Rensing1, and Sylvia Franke
  • Editor: Valley Stewart2
  • VIEW AFFILIATIONS HIDE AFFILIATIONS
    Affiliations: 1: Department of Soil, Water, and Environmental Science, Shantz Bldg. #38, Rm. 429, University of Arizona, Tucson, AZ 85721; 2: University of California, Davis, Davis, CA
  • Received 23 August 2006 Accepted 31 October 2006 Published 11 January 2007
  • Address correspondence to Christopher Rensing rensingc@ag.arizona.edu
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  • Abstract:

    An interesting model for studying environmental influences shaping microbial evolution is provided by a multitude of copper resistance and copper homeostasis determinants in enteric bacteria. This review describes these determinants and tries to relate their presence to the habitat of the respective organism, as a current hypothesis predicts that the environment should determine an organism’s genetic makeup. In there are four regulons that are induced in the presence of copper. Two, the CueR and the CusR regulons, are described in detail. A central component regulating intracellular copper levels, present in all free-living enteric bacteria whose genomes have so far been sequenced, is a Cu(I)translocating P-type ATPase. The P-type ATPase superfamily is a ubiquitous group of proteins involved in the transport of charged substrates across biological membranes. Whereas some components involved in copper homeostasis can be found in both anaerobes and aerobes, multi-copper oxidases (MCOs) implicated in copper tolerance in , such as CueO and the plasmid-based PcoA, can be found only in aerobic organisms. Several features indicate that CueO, PcoA, and other related MCOs are specifically adapted to combat copper-mediated oxidative damage. In addition to these well-characterized resistance operons, there are numerous other genes that appear to be involved in copper binding and trafficking that have not been studied in great detail. SilE and its homologue PcoE, for example, are thought to effect the periplasmic binding and sequestration of silver and copper, respectively.

  • Citation: Rensing C, Franke S. 2007. Copper Homeostasis in and Other , EcoSal Plus 2007; doi:10.1128/ecosalplus.5.4.4.1

Key Concept Ranking

Outer Membrane Proteins
0.45599452
Mobile Genetic Elements
0.4036893
Reactive Oxygen Species
0.38861147
Horizontal Gene Transfer
0.38197985
General Stress Response
0.35294148
0.45599452

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/content/journal/ecosalplus/10.1128/ecosalplus.5.4.4.1
2007-01-11
2017-05-27

Abstract:

An interesting model for studying environmental influences shaping microbial evolution is provided by a multitude of copper resistance and copper homeostasis determinants in enteric bacteria. This review describes these determinants and tries to relate their presence to the habitat of the respective organism, as a current hypothesis predicts that the environment should determine an organism’s genetic makeup. In there are four regulons that are induced in the presence of copper. Two, the CueR and the CusR regulons, are described in detail. A central component regulating intracellular copper levels, present in all free-living enteric bacteria whose genomes have so far been sequenced, is a Cu(I)translocating P-type ATPase. The P-type ATPase superfamily is a ubiquitous group of proteins involved in the transport of charged substrates across biological membranes. Whereas some components involved in copper homeostasis can be found in both anaerobes and aerobes, multi-copper oxidases (MCOs) implicated in copper tolerance in , such as CueO and the plasmid-based PcoA, can be found only in aerobic organisms. Several features indicate that CueO, PcoA, and other related MCOs are specifically adapted to combat copper-mediated oxidative damage. In addition to these well-characterized resistance operons, there are numerous other genes that appear to be involved in copper binding and trafficking that have not been studied in great detail. SilE and its homologue PcoE, for example, are thought to effect the periplasmic binding and sequestration of silver and copper, respectively.

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Figures

Image of Figure 1
Figure 1

contains three major chromosomally encoded copper homeostasis mechanisms. Copper is transported across the cytoplasmic membrane (CM) as Cu(I) via CopA, a P-type ATPase, into the periplasmic space. However, in the periplasm copper can cause damage to proteins and lipids by undergoing redox cycling. Therefore, Cu(I) is oxidized into Cu(II) via the multicopper oxidase CueO under aerobic conditions. In addition, CueO oxidizes catechol siderophores such as enterobactin and thus prevents enterobactin-mediated reduction of Cu(II) to Cu(I). Oxidized enterobactin is able to bind copper and reduce the concentration of free copper that can undergo the redox cycling. Under anaerobic conditions or in the absence of CueO, copper [probably as Cu(I)] is translocated from the periplasm into the surrounding medium via the CusC(F)BA complex. The CusCBA components form a protein complex stretching from the cytoplasmic membrane to the outer membrane (OM) as described for the TolC-AcrAB complex ( 4 , 5 ). Cu(I) is thought to enter the transport complex from the periplasmic side (either by itself or transported to CusCBA via CusF), where it is then transported across the outer membrane. Copper ions, both Cu(I) and Cu(II), are drawn as blue circles with transparent blue indicating copper bound to proteins or enterobactin.

Citation: Rensing C, Franke S. 2007. Copper Homeostasis in and Other , EcoSal Plus 2007; doi:10.1128/ecosalplus.5.4.4.1
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Image of Figure 2
Figure 2

CopA of contains eight transmembrane helices (labeled I to VIII) with N and C termini located in the cytoplasm. The N terminus contains two metal binding domains (CXC) consisting of cysteines C14, C17, C110, and C113. Also in the cytoplasm are the functionally important beta-loop (T374 to P377), the phosphorylation domain (p-domain; D523 to G526), and the N domain (G719 to P726). Residues thought to be involved in substrate specificity besides the CPC motif in transmembrane VI (C479 to C481) are residues Y784 and N785 located in transmembrane VII as well as M813 and S817 located in transmembrane VIII ( 24 ).

Citation: Rensing C, Franke S. 2007. Copper Homeostasis in and Other , EcoSal Plus 2007; doi:10.1128/ecosalplus.5.4.4.1
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Image of Figure 3
Figure 3

(A) Ribbon diagram of CueO. Shown is the three-dimensional structure of CueO, including the copper centers T1 (“blue copper”), T2, and T3 (“trinuclear cluster”). A fifth copper atom is bound at the base of the methionine-rich helix and is essential for the oxidase activity of CueO. (B) Scheme of catalysis for the multicopper oxidase CueO. Electrons are transferred from the substrate (S), which is thereby oxidized to the product (P) via the regulatory copper (rCu) to the T1 (“blue”) copper center and from there to the trinuclear cluster (T2, T3), where oxygen is reduced to HO. Whereas the electrons are first transferred to the regulatory copper in CueO, the electron transfer in other MCOs (laccases, ascorbate oxidase, ceruloplasmin) is directly from the substrate to the copper in the T1 copper center (data not shown).

Citation: Rensing C, Franke S. 2007. Copper Homeostasis in and Other , EcoSal Plus 2007; doi:10.1128/ecosalplus.5.4.4.1
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Image of Figure 4
Figure 4

CusF is shown as a ribbon diagram. Residues undergoing a significant change in chemical shift in nuclear magnetic resonance experiments after addition of Cu(I) are labeled in red. The side chains of the residues most likely involved in coordinating Cu(I), H36, M47, and M49, are shown.

Citation: Rensing C, Franke S. 2007. Copper Homeostasis in and Other , EcoSal Plus 2007; doi:10.1128/ecosalplus.5.4.4.1
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Tables

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Table 1

Overview of copper and silver resistance systems among

Citation: Rensing C, Franke S. 2007. Copper Homeostasis in and Other , EcoSal Plus 2007; doi:10.1128/ecosalplus.5.4.4.1

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