Enhancement of copper content and specific activity of CotA laccase from Bacillus licheniformis by coexpression with CopZ copper chaperone in E. coli

Biochemical characterization of a recombinant laccase from Halalkalibacterium halodurans C-125 and its application in the biotransformation of organic compounds

OBJECTIVES

This study aimed to produce an engineered recombinant laccase from extremophilic Halalkalibacterium halodurans C-125 (Lac-HhC-125) with higher protein yield, into a more active conformation and with properties that meet the fundamental needs of biotechnological application.

RESULTS

The rLac-HhC125 was partially purified by size exclusion chromatography and concentrated by ultrafiltration (10 kDa) with a yield of 57.6%. Oxidation reactions showed that adding 2 mM CuSO4 to the assay solution led to activating the laccase. To increase its initial activity, the rLac-HhC125 was treated at 50 °C for 20 min before the assays, improving its performance by fourfold using the syringaldazine as a substrate. When treated with EDTA, methanol, ethanol, and DMSO, the rLac-HhC125 maintained more than 80% of its original activity. Interestingly, the acetonitrile induced a twofold activity of the rLac-HhC125. The putative rLac-HhC125 demonstrated a capability of efficient transformation of different organic compounds at pH 6, known as dye precursors, into coloured molecules.

CONCLUSION

The rLac-HhC125 was active at high temperatures and alkaline pH, exhibited tolerance to organic solvents, and efficiently transformed different hydroxy derivatives into coloured compounds, which indicates that it can be used in various biotechnological processes.

Moving metals: How microbes deliver metal cofactors to metalloproteins

First row d-block metal ions serve as vital cofactors for numerous essential enzymes and are therefore required nutrients for all forms of life. Despite this requirement, excess free transition metals are toxic. Free metal ions participate in the production of noxious reactive oxygen species and mis-metalate metalloproteins, rendering enzymes catalytically inactive. Thus, bacteria require systems to ensure metalloproteins are properly loaded with cognate metal ions to maintain protein function, while avoiding metal-mediated cellular toxicity. In this perspective we summarize the current mechanistic understanding of bacterial metallocenter maturation with specific emphasis on metallochaperones; a group of specialized proteins that both shield metal ions from inadvertent reactions and distribute them to cognate target metalloproteins. We highlight several recent advances in the field that have implicated new classes of proteins in the distribution of metal ions within bacterial proteins, while speculating on the future of the field of bacterial metallobiology.

Isolation, Purification, and Characterization of a Laccase-Degrading Aflatoxin B1 from Bacillus amyloliquefaciens B10

Aflatoxins, widely found in feed and foodstuffs, are potentially harmful to human and animal health because of their high toxicity. In this study, a strain of Bacillus amyloliquefaciens B10 with a strong ability to degrade aflatoxin B1 (AFB1) was screened; it could degrade 2.5 μg/mL of AFB1 within 96 h. The active substances of Bacillus amyloliquefaciens B10 for the degradation of AFB1 mainly existed in the culture supernatant. A new laccase with AFB1-degrading activity was separated by ammonium sulfate precipitation, diethylaminoethyl (DEAE) and gel filtration chromatography. The results of molecular docking showed that B10 laccase and aflatoxin had a high docking score. The coding sequence of the laccase was successfully amplified from cDNA by PCR and cloned into E. coli. The purified laccase could degrade 79.3% of AFB1 within 36 h. The optimum temperature for AFB1 degradation was 40 °C, and the optimum pH was 6.0–8.0. Notably, Mg²⁺ and dimethyl sulfoxide (DMSO) could enhance the AFB1-degrading activity of B10 laccase. Mutation of the three key metal combined sites of B10 laccase resulted in the loss of AFB1-degrading activity, indicating that these three metal combined sites of B10 laccase play an essential role in the catalytic degradation of AFB1.

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.

The Cu chaperone CopZ is required for Cu homeostasis in Rhodobacter capsulatus and influences cytochrome cbb3 oxidase assembly

Cu homeostasis depends on a tightly regulated network of proteins that transport or sequester Cu, preventing the accumulation of this toxic metal while sustaining Cu supply for cuproproteins. In Rhodobacter capsulatus, Cu-detoxification and Cu delivery for cytochrome c oxidase (cbb₃ -Cox) assembly depend on two distinct Cu-exporting P_1B -type ATPases. The low-affinity CopA is suggested to export excess Cu and the high-affinity CcoI feeds Cu into a periplasmic Cu relay system required for cbb₃ -Cox biogenesis. In most organisms, CopA-like ATPases receive Cu for export from small Cu chaperones like CopZ. However, whether these chaperones are also involved in Cu export via CcoI-like ATPases is unknown. Here we identified a CopZ-like chaperone in R. capsulatus, determined its cellular concentration and its Cu binding activity. Our data demonstrate that CopZ has a strong propensity to form redox-sensitive dimers via two conserved cysteine residues. A ΔcopZ strain, like a ΔcopA strain, is Cu-sensitive and accumulates intracellular Cu. In the absence of CopZ, cbb₃ -Cox activity is reduced, suggesting that CopZ not only supplies Cu to P_1B -type ATPases for detoxification but also for cuproprotein assembly via CcoI. This finding was further supported by the identification of a ~150 kDa CcoI-CopZ protein complex in native R. capsulatus membranes.

Activity enhancement of CotA laccase by hydrophilic engineering, histidine tag optimization and static culture

CotA protein from Bacillus subtilis is of laccase activity. The solubility of recombinant CotA is low, which hinders its application. In this study, histidine tag position optimization and hydrophilic engineering were applied to increase the yield and activity of CotA protein. The results showed that the protein yield of CotA with his tag at C-terminal (CH6-CotA) was four times of that of NH6-CotA (His tag at N-terminal). Then, 23 single mutants were constructed by substitutions of hydrophobic residues with hydrophilic amino acids. Among them, the protein yield of the mutant F207Y was increased by 30%; the catalytic activity (kcat/Km) of V403T and P455S was two and three times higher than that of CH6-CotA, respectively. Finally, triple mutant F2071Y/V403T/P455S with C-terminal his-tag (CH6-TSY) was constructed. When the proteins were expressed in microanaerobic condition, the activities of mutants CH6-P455S and CH6-TSY were enhanced about 48- and 42-folds compared to that of NH6-CotA in non-static culture.

Heterologous expression of a Streptomyces cyaneus laccase for biomass modification applications

Laccases are used for the conversion of biomass into fermentable sugars but it is difficult to produce high yields of active laccases in heterologous expression systems. We overcame this challenge by expressing Streptomyces cyaneus CECT 3335 laccase in Escherichia coli (ScLac) and we achieved a yield of up to 104 mg L-1 following purification by one-step affinity chromatography. Stability and activity assays using simple lignin model substrates showed that the purified enzyme preparation was active over a broad pH range and at high temperatures, suggesting it would be suitable for biomass degradation. The reusability of ScLac was also demonstrated by immobilizing the enzyme on agarose beads with a binding yield of 33%, and by the synthesis of cross-linked enzyme aggregates with an initial activity recovery of 72%.

Recombinant laccase from Pediococcus acidilactici CECT 5930 with ability to degrade tyramine

Biogenic amines degradation by bacterial laccases is little known, so we have cloned and heterologously expressed, in E. coli, a new laccase from Pediococcus acidilactici CECT 5930 (Lpa5930), a lactic acid bacterium commonly found in foods able to degrade tyramine. The recombinant enzyme has been characterized by physical and biochemical assays. Here we report the optimization of expression and purification procedures of this laccase. DNA encoding sequence of laccase from P. acidilactici was amplified by PCR and cloned into the expression plasmid pET28a for induction by isopropyl-β-D-thiogalactoipyranoside. Protein expression was performed in E. coli BL21(DE3) harboring pGro7 plasmid expressing a chaperone folding assistant induced by arabinose. Purification was performed by column metal-chelating chromatography on Ni-NTA-agarose. The laccase enzyme obtained has an apparent molecular mass of ∼60 kDa, an optimum temperature activity toward 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) of 28°C, and was quickly inactivated at temperatures higher than 70°C. The apparent Km value for ABTS was 1.7 mM and the Vmax obtained was 24 U/mg. In addition to ABTS, recombinant Lpa5930 laccase degraded the biogenic amine tyramine at pH 9.5 and pH 4.0 with or without ABTS as a mediator. Tyramine degradation by laccases could solve the problems generated in food due to the presence of this toxic compound.

Upgrading Laccase Production and Biochemical Properties: Strategies and Challenges

Improving laccases continues to be crucial in novel biotechnological developments and industrial applications, where they are concerned. This review breaks down and explores the potential of the strategies (conventional and modern) that can be used for laccase enhancement (increased production and upgraded biochemical properties such as stability and catalytic efficiency). The challenges faced with these approaches are briefly discussed. We also shed light on how these strategies merge and give rise to new options and advances in this field of work. Additionally, this article seeks to serve as a guide for students and academic researchers interested in laccases. This document not only gives basic information on laccases, but also provides updated information on the state of the art of various technologies that are used in this line of investigation. It also gives the readers an idea of the areas extensively studied and the areas where there is still much left to be done. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1015-1034, 2017.

Enhancement of Solubility and Specific Activity of a Cu/Zn Superoxide Dismutase by Co-expression with a Copper Chaperone in Escherichia coli

BACKGROUND

Human Cu/Zn superoxide dismutase (hSOD1) is an antioxidant enzyme with potential as a therapeutic agent. However, heterologous expression of hSOD1 has remained an issue due to Cu²⁺ insufficiency at protein active site, leading to low solubility and enzymatic activity.

OBJECTIVES

The effect of co-expressed human copper chaperone (hCCS) to enhance the solubility and enzymatic activity of hSOD1 in E. coli was investigated in the presence and absence of Cu²⁺.

MATERIALS AND METHODS

pETDuet-1-hSOD1 and pETDuet-1-hCCS-hSOD1 were constructed and individually transformed into E. coli strain BL21(DE3). The recombinant hSOD1 was expressed and purified using immobilized metal affinity chromatography. The yield and specific activity of hSOD1 in all conditions were studied.

RESULTS

Co-expression with hCCS increased hSOD1 solubility at 37°C, but this effect was not observed at 25°C. Notably, the specific activity of hSOD1 was enhanced by 1.5 fold and greater than 3 fold when co-expressed with hCCS at 25°C with and without Cu²⁺ supplement, respectively. However, the chaperone co-expression did not significantly increase the yield of hSOD1 comparable to the expression of hSOD1 alone.

CONCLUSIONS

This study is the first report demonstrating a potential use of hCCS for heterologous production of hSOD1 with high enzymatic activity.

Hydrogen Peroxide-Resistant CotA and YjqC of Bacillus altitudinis Spores Are a Promising Biocatalyst for Catalyzing Reduction of Sinapic Acid and Sinapine in Rapeseed Meal

For the more efficient detoxification of phenolic compounds, a promising avenue would be to develop a multi-enzyme biocatalyst comprising peroxidase, laccase and other oxidases. However, the development of this multi-enzyme biocatalyst is limited by the vulnerability of fungal laccases and peroxidases to hydrogen peroxide (H2O2)-induced inactivation. Therefore, H2O2-resistant peroxidase and laccase should be exploited. In this study, H2O2-stable CotA and YjqC were isolated from the outer coat of Bacillus altitudinis SYBC hb4 spores. In addition to the thermal and alkali stability of catalytic activity, CotA also exhibited a much higher H2O2 tolerance than fungal laccases from Trametes versicolor and Trametes trogii. YjqC is a sporulation-related manganese (Mn) catalase with striking peroxidase activity for sinapic acid (SA) and sinapine (SNP). In contrast to the typical heme-containing peroxidases, the peroxidase activity of YjqC was also highly resistant to inhibition by H2O2 and heat. CotA could also catalyze the oxidation of SA and SNP. CotA had a much higher affinity for SA than B. subtilis CotA. CotA and YjqC rendered from B. altitudinis spores had promising laccase and peroxidase activities for SA and SNP. Specifically, the B. altitudinis spores could be regarded as a multi-enzyme biocatalyst composed of CotA and YjqC. The B. altitudinis spores were efficient for catalyzing the degradation of SA and SNP in rapeseed meal. Moreover, efficiency of the spore-catalyzed degradation of SA and SNP was greatly improved by the presence of 15 mM H2O2. This effect was largely attributed to synergistic biocatalysis of the H2O2-resistant CotA and YjqC toward SA and SNP.

Increasing the catalytic activity of Bilirubin oxidase from Bacillus pumilus: Importance of host strain and chaperones proteins

Aggregation of recombinant proteins into inclusion bodies (IBs) is the main problem of the expression of multicopper oxidase in Escherichia coli. It is usually attributed to inefficient folding of proteins due to the lack of copper and/or unavailability of chaperone proteins. The general strategies reported to overcome this issue have been focused on increasing the intracellular copper concentration. Here we report a complementary method to optimize the expression in E. coli of a promising Bilirubin oxidase (BOD) isolated from Bacillus pumilus. First, as this BOD has a disulfide bridge, we switched E.coli strain from BL21 (DE3) to Origami B (DE3), known to promote the formation of disulfide bridges in the bacterial cytoplasm. In a second step, we investigate the effect of co-expression of chaperone proteins on the protein production and specific activity. Our strategy allowed increasing the final amount of enzyme by 858% and its catalytic rate constant by 83%.

A strategy for soluble overexpression and biochemical characterization of halo-thermotolerant Bacillus laccase in modified E. coli

An efficient method was introduced for soluble expression of recombinant laccase (rpCotA(SL-1)) from a newly isolated halo-thermotolerant Bacillus sp. SL-1 in modified Escherichia coli, trxB2/gor2 mutant (Origami™ B (DE3)). The yield of purified soluble laccase in Origami strain under micro-aerobic condition was ∼20mg/L of bacterial culture, showing significant improvement over the laccase produced in E.coli BL21 strain under aerobic condition. The specific activity of 13U/mg for purified laccase produced in micro-aerobic condition was higher than that of 1.07U/mg observed for the purified enzyme obtained in aerobic condition in Origami. The kinetic Km and kcat parameters for laccase-induced oxidation reactions were 46μM and 23s(-1) for ABTS (2,2'-Azino-bis(3-ethylbenzthiazoline-6-sulphonic acid), and 19.6μM and 24s(-1) for SGZ (syringaldazine) substrates, respectively. The rpCotA(SL-1) displayed thermostability at 70°C and tolerance to specified concentrations of NaCl, NaN3, EDTA and SDS as inhibitors. The enzyme was relatively stable in the presence of different concentration of organic solvents, however the residual activity was adversely affected as the dipole moment of the solvents increase. Here we successfully report the production of soluble and functional laccase in Origami at the expression level suitable for industrial application.

Biochemical properties and yields of diverse bacterial laccase-like multicopper oxidases expressed in Escherichia coli

Laccases are multi-copper oxidases that oxidize a broad range of substrates at the expense of molecular oxygen, without any need for co-factor regeneration. These enzymes bear high potential for the sustainable synthesis of fine chemicals and the modification of (bio)polymers. Here we describe cloning and expression of five novel bacterial laccase-like multi copper oxidases (LMCOs) of diverse origin which were identified by homology searches in online databases. Activity yields under different expression conditions and temperature stabilities were compared to three previously described enzymes from Bacillus subtilis, Bacillus pumilus and Bacillus clausii. In almost all cases, a switch to oxygen-limited growth conditions after induction increased volumetric activity considerably. For proteins with predicted signal peptides for secretion, recombinant expression with and without signal sequence was investigated. Bacillus CotA-type LMCOs outperformed enzymes from Streptomyces and Gram-negative bacteria with respect to activity yields in Escherichia coli and application relevant biochemical properties. The novel Bacillus coagulans LMCO combined high activity yields in E. coli with unprecedented activity at strong alkaline pH and high storage stability, making it a promising candidate for further development.