Enhanced expression of a recombinant multicopper oxidase, CueO, from Escherichia coli and its laccase activity towards aromatic substrates

Molecular cloning, expression, and bioinformatics analysis of the CueO laccase gene from Escherichia coli SDB2

BACKGROUND

Laccase CueO, a multicopper oxidase, possesses the capability to degrade phenolic compounds. In prior research, a strain of Escherichia coli named SDB2, isolated from chicken cecum, was found to degrade sinapine (a phenolic constituent of rapeseed meal) through the secretion of laccase CueO. Herein, the cloning, expression, and bioinformatics analysis of the CueO gene derived from E. coli SDB2 are reported.

METHODS AND RESULTS

Sequence analysis indicated that SDB2 CueO comprised 1551 bp, 516 amino acids, a putative molecular weight of 56.65 kDa, and an isoelectric point (pI) of 6.21. BLAST comparisons showed that the CueO protein sequence from E. coli SDB2 exhibited 65-90% identity with CueO from other bacteria. Multiple alignment analysis further confirmed the similarity and identity of SDB2 CueO with CueO from other species, and the amino acids surrounding the Cu-binding sites were highly conserved. A phylogenetic tree demonstrated a close evolutionary relationship between CueO from E. coli and CueO from Citrobacter amalonaticus. The three-dimensional (3D) structural model revealed four copper (Cu)-binding regions. Recombinant CueO was successfully obtained by expressing the CueO gene in E. coli BL21 after isopropyl β-D-1-thiogalactopyranoside (IPTG) induction. Bioinformatics analysis confirmed the similarity of recombinant CueO with native CueO.

CONCLUSIONS

These findings established a basis for understanding the characteristics and functions of laccase CueO from E. coli SDB2, paving the way for future research to explore the properties of recombinant CueO and its potential practical applications in optimizing feed resources, such as rapeseed meal, in the feed production industry.

Degradation of octylphenol polyethoxylates with a long ethoxylate chain using the laccase-mediated systems

Alkylphenol polyethoxylates (APEOn) are the second-largest category of commercial nonionic surfactants, which are difficult to degrade naturally in the environment. This study examined the degradation of octylphenol polyethoxylate (OPEOn) by laccase and its laccase-mediated systems. The results showed that OPEOn was poorly degraded by laccase alone. 2, 2'-azino-bis [3-ethylbenzothiazoline-6-sulphonic acid] (ABTS), 1-hydroxybenzotriazole (HBT), and 2, 2, 6, 6-tetramethylpiperidine-1-oxyl (TEMPO) were selected as the redox mediators. Experimental results also indicated that 52.4% of the initial OPEOn amount was degraded by laccase in the presence of TEMPO. The degradation efficiency was analyzed using high-performance liquid chromatography. Furthermore, the structural characteristics of the degradation products were measured using matrix-assisted laser desorption/ionization-time of flight mass spectrometry and nuclear magnetic resonance spectroscopy, and it could be found that the laccase-TEMPO system could gradually shorten the ethoxylate chain by oxidizing the primary hydroxyl group of OPEOn, thereby degrading the OPEOn of the macromolecule into small molecules. The maximum of the ion peak distributions of OPEOn decreased from n = 8 finally down to 3. The novel enzymatic system introduced by this study will become a promising alternative method for high-efficiency APEOn conversion and had great potential value in wastewater treatment.

Use of Copper as a Trigger for the in Vivo Activity of E. coli Laccase CueO: A Simple Tool for Biosynthetic Purposes

Laccases are multi-copper oxidases that catalyze the oxidation of various electron-rich substrates with concomitant reduction of molecular oxygen to water. The multi-copper oxidase/laccase CueO of Escherichia coli is responsible for the oxidation of Cu+ to the less harmful Cu2+ in the periplasm. CueO has a relatively broad substrate spectrum as laccase, and its activity is enhanced by copper excess. The aim of this study was to trigger CueO activity in vivo for the use in biocatalysis. The addition of 5 mM CuSO4 was proven effective in triggering CueO activity at need with minor toxic effects on E. coli cells. Cu-treated E. coli cells were able to convert several phenolic compounds to the corresponding dimers. Finally, the endogenous CueO activity was applied to a four-step cascade, in which coniferyl alcohol was converted to the valuable plant lignan (-)-matairesinol.