Designed by: Jan Lars Kalkowski   Group: iGEM20_TU_Darmstadt   (2020-10-16)

Blue copper oxidase CueO


Name Copper efflux oxidase CueO
Base pairs 1551
Molecular weight 56.58 kDa
Origin Escherichia coli, synthetic
Properties Copper efflux oxidase CueO from Eschericha coli is a copper dependant bacterial laccase possesing five coordinated copper ions relevant for electron transfer. The Cu-ions are coordinated as a T1, three T2/3-cluster Cus and a fifth weakly coordinated copper. CueO differs from most other laccases in its fifth copper binding site[1].

This part was designed for in vitro characterization.

Contribution: Team Aboa 2021

Here we provide new information from literature of the laccase CueO.


Laccases are multi-copper oxidases (MCOs) that can catalyze reactions of many substrates, for example organic compounds, dyes and pharmaceuticals. They can be found in fungi, bacteria, insects and plants and they are involved in many different functions, for example in lignin degradation, pigmentation, pathogenesis of fungi and wound healing in plants.[2] CueO is a multicopper oxidase laccase produced by E. coli [3].

In vitro, CueO can oxidise various compounds, such as catechols, ferrous iron and iron-chelating siderophores [4]. It has been proven that CueO plays a pivotal role in regulating the copper resistance of E. coli [5]. The mechanism of action of CueO in vivo has been suggested to be the cuprous oxidation in which CueO confers more toxic Cu(I) to less toxic Cu(II). According to one study, the optimal pH for the proper CueO function is 6,5. [3]

Figure 1. The proposed mechanism of CueO as a cuprous oxidative agent. In this example, the substrate is [Cu(I)(Bca)2]3- in the BisTris Buffer. The red sphere indicates a Cu(I) atom whereas the blue sphere indicates a Cu(II) atom. The picture illustrates how the T4 site changes from an empty resting state (i) to the copper-binding (ii-iii) and copper-oxidating states (iv). [7]

Coppers play a major role in the oxidation reactions of MCOs due to their central location in catalytic sites. It has also been previously shown that the oxidation activity of CueO depends on copper concentrations. [6] In general, MCOs contain four copper atoms in different sites; in a T1 site (“blue” copper), in a T2 site (“normal” copper) and in two types of T3 sites (“binuclear” coppers) [3]. When it comes to a reaction of CueO, the T1 site acts as an electron transfer site whereas T2 and T3 perform dioxygen reduction [7]. Unlike other multicopper oxidases, CueO requires five copper atoms and it has a methionine-rich helix that functions as a valuable regulative element regarding copper binding [4]. In the absence of copper, that helix acts by blocking access to the T1 site and simultaneously providing a new copper-binding site T4 [3,7]. It has been shown that the deletion of this helix leads to a remarkably decreased oxidation activity which highlights the importance of the T4 site in the CueO function. In Figure 1, you can see the proposed reaction mechanism for CueO oxidative function illustrated with an example substrate compound [Cu(I)(Bca)2]3- in BisTris Buffer. [7]


The structure of CueO has been succeeded to determine at 1,4 Å resolution, which allows a precise positioning of copper binding sites. CueO is composed of three pseudoazurin domains. Both the T1 site and a methionine-rich helix are located in domain 3. [3] The methionine-rich helix provides an extra copper-binding site T4, which is only 7.5 Å away from the T1 site [7].

Sequence and Features

Assembly Compatibility:
  • 10
  • 12
  • 21
  • 23
  • 25
  • 1000

[1] L. Zhang et al. Directed Evolution of a Bacterial Laccase (CueO) for Enzymatic Biofuel Cells. Angewandte Chemie 2019, 58 (14) 4562-4565,
[2] L. Arregui et al. Laccases: structure, function, and potential application in water bioremediation. Microbial Cell Factories 2009, 18 (1) 200,
[3] S. Roberts et al. Crystal structure and electron transfer kinetics of CueO, a multicopper oxidase required for copper homeostasis in Escherichia coli. Proceedings of the National Academy of Sciences of the United States of America 2002, 99 (5) 2766-2771,
[4] S. Singh et al. Cuprous Oxidase Activity of CueO from Escherichia coli. Journal of Bacteriology 2004, 186 (22) 7815-7817,
[5] G. Grass and C. Rensing. CueO is a multi-copper oxidase that confers copper tolerance in Escherichia coli. Biochemical and biophysical research communications 2001, 286 (5) 902-908,
[6] X. Li et al. Crystal structures of E. coli laccase CueO at different copper concentrations. Biochemical and biophysical research communications 2007, 354 (1) 21-26,
[7] K. Djoko et al. Reaction Mechanisms of the multicopper oxidase CueO from Escherichia coli support its functional role as a cuprous oxidase. Journal of the American Chemical Society 2010, 132 (6) 2005-2015,