Sequential reconstitution of copper sites in the multicopper oxidase CueO

Methionine-rich domains emerge as facilitators of copper recruitment in detoxification systems

Copper homeostasis mechanisms are critical for bacterial resistance to copper-induced stress. The Escherichia coli multicopper oxidase copper efflux oxidase (CueO) is part of the copper detoxification system in aerobic conditions. CueO contains a methionine-rich (Met-rich) domain believed to interact with copper, but its exact function and the importance of related copper-binding sites remain unclear. This study investigates these open questions by employing a multimodal and multiscale approach. Through the design of various E. coli CueO (EcCueO) variants with altered copper-coordinating residues and domain deletions, we employ biological, biochemical, and physico-chemical approaches to unravel in vitro CueO catalytic properties and in vivo copper resistance. Strong correlation between the different methods enables evaluation of EcCueO variants' activity as a function of Cu+ availability. Our findings demonstrate the Met-rich domain is not essential for cuprous oxidation, but it facilitates Cu+ recruitment from strongly chelated forms, acting as transient copper binding domain thanks to multiple methionines. They also indicate that the Cu6/7 copper-binding sites previously observed within the Met-rich domain play a negligible role. Meanwhile, Cu5, located at the interface with the Met-rich domain, emerges as the primary and sole substrate-binding active site for cuprous oxidation. The Cu5 coordination sphere strongly affects the enzyme activity and the in vivo copper resistance. This study provides insights into the nuanced role of CueO Met-rich domain, enabling the functions of copper-binding sites and the entire domain itself to be decoupled. This paves the way for a deeper understanding of Met-rich domains in the context of bacterial copper homeostasis.

The copper P-type ATPase CtpA is involved in the response of Mycobacterium tuberculosis to redox stress

The functional difference among the three copper-transporting P-type ATPases (CtpA, CtpB, and CtpV) annotated in genome of Mycobacterium tuberculosis (Mtb) remains unclear. Thus, CtpA and CtpB are believed to deliver copper to extracytoplasmic proteins as a cofactor required to overcome redox and copper stress in the Mtb periplasm. This study investigates an alternative role of CtpA-mediated copper transportation and its possible interaction with the activity of the multicopper oxidase, (MmcO), in response to redox stress. Results from RT-qPCR experiments indicate that the ctpA gene is upregulated in low Cu2+ concentrations, and under oxidative (H2O2) and nitrosative (sodium nitroprusside) conditions in vitro, but not in high doses of Cu2+. Furthermore, the ctpA mutant strain (MtbΔctpA) showed impaired growth in the presence of oxidative and nitrosative stress in vitro. However, it did not display such growth impairments in response to high doses of copper in comparison to the wild-type strain. Disruption of the ctpA gene in the Mtb genome did not induce an accumulation of copper in cells under toxic doses of the metal, suggesting that CtpA is not directly involved in copper detoxification. On the other hand, whole-cell lysates of the MtbΔctpA mutant that were previously stimulated with Cu2+, H2O2 and SNP (sodium nitroprusside), displayed reduced ability to oxidize organic substrates (para-phenylenediamine (pPD) and 2,2-azino-bis (3-ethylbenzothiazo-line-6-sulfonic acid) (ABTS). These finding strongly suggest that the efflux of copper transported by CtpA from the cytoplasm is relevant to the response to the redox stress and may be required for metalation and activity of MmcO in Mtb.

Heterologous Expression and Application of Multicopper Oxidases from Enterococcus spp. for Degradation of Biogenic Amines

BACKGROUND

Biogenic amines are harmful to human health at a certain extent. As a kind of biogenic amine oxidase, multicopper oxidase can be used to degrade them. Currently, the literature about enzyme from Enterococcus spp. are limited, and recombinant multicopper oxidase might be an effective way to degrade biogenic amines.

OBJECTIVE

(i) Select and identify strains that can degrade biogenic amines, (ii) overexpress enzyme from Enterococcus spp., (iii) measure gene expression and probe amine-degradation differences among strains (native, E. coli DH5α, and L. delbruckii), and (iv) examine the biochemical properties of recombinant multicopper oxidase, (v) apply the recombinant enzyme into smoked horsemeat sausage.

METHODS

Reverse transcription PCR and high-performance liquid chromatography were performed to examine gene expression and amine degradation rate.

RESULTS

The results demonstrated that target enzymes were successfully overexpressed, accompanied by increased amine-degrading activity (P <0.05). Gene from E. faecalis M5B was expressed in L. delbrueckii resulted in degradation rates for phenylethylamine, putrescine, histamine and tyramine of 54%, 52%, 70% and 40%, respectively, significantly higher than achieved by other recombinant strains.

CONCLUSION

In this work, gene expression levels were higher in recombinant M5B than recombinant M2B, regardless of host. E. coli is more stable to express multicopper oxidase. Besides, the amine-degrading ability was markedly increased in the two recombinant strains. After prolonged incubation, the recombinant enzyme could degrade three amines, and it displayed high alkali resistance and thermostability.

Mutations in the coordination spheres of T1 Cu affect Cu2+-activation of the laccase from Thermus thermophilus

Thermus thermophilus laccase belongs to the sub-class of multicopper oxidases that is activated by the extra binding of copper to a methionine-rich domain allowing an electron pathway from the substrate to the conventional first electron acceptor, the T1 Cu. In this work, two key amino acid residues in the 1st and 2nd coordination spheres of T1 Cu are mutated in view of tuning their redox potential and investigating their influence on copper-related activity. Evolution of the kinetic parameters after copper addition highlights that both mutations play a key role influencing the enzymatic activity in distinct unexpected ways. These results clearly indicate that the methionine rich domain is not the only actor in the cuprous oxidase activity of CueO-like enzymes.

Stability/activity tradeoffs in Thermusthermophilus HB27 laccase

We report the temperature dependence of the formal potential of type 1 copper (Cu_T1) in Thermusthermophilus HB27 laccase. Employing [Ru(NH₃)₄(bpy)](PF₆)₂ (0.505 vs. NHE) as the redox titrant, we found that the Cu_T1^2+/+ potential decreased from approximately 480 to 420 mV (vs. NHE) as the temperature was raised from 20 to 65 °C. Of importance is that the ΔS_rc° of - 120 J mol^-1 K^-1 is substantially more negative than those for other blue copper proteins. We suggest that the highly unfavorable reduction entropy is attributable to Cu_T1 inaccessibility to the aqueous medium. Although the active site residues are buried, which is critical for maintaining thermostability, the flexibility around Cu_T1 is maintained, allowing enzyme activity at ambient temperature.

Crystal structures of multicopper oxidase CueO G304K mutant: structural basis of the increased laccase activity

The multicopper oxidase CueO is involved in copper homeostasis and copper (Cu) tolerance in Escherichia coli. The laccase activity of CueO G304K mutant is higher than wild-type CueO. To explain this increase in activity, we solved the crystal structure of G304K mutant at 1.49 Å. Compared with wild-type CueO, the G304K mutant showed dramatic conformational changes in methionine-rich helix and the relative regulatory loop (R-loop). We further solved the structure of Cu-soaked enzyme, and found that the addition of Cu ions induced further conformational changes in the R-loop and methionine-rich helix as a result of the new Cu-binding sites on the enzyme's surface. We propose a mechanism for the enhanced laccase activity of the G304K mutant, where movements of the R-loop combined with the changes of the methionine-rich region uncover the T1 Cu site allowing greater access of the substrate. Two of the G304K double mutants showed the enhanced or decreased laccase activity, providing further evidence for the interaction between the R-loop and the methionine-rich region. The cuprous oxidase activity of these mutants was about 20% that of wild-type CueO. These structural features of the G304K mutant provide clues for designing specific substrate-binding mutants in the biotechnological applications.

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.

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%.

The Tat Substrate CueO Is Transported in an Incomplete Folding State

In Escherichia coli, cytoplasmic copper ions are toxic to cells even at the lowest concentrations. As a defense strategy, the cuprous oxidase CueO is secreted into the periplasm to oxidize the more membrane-permeable and toxic Cu(I) before it can enter the cytoplasm. CueO itself is a multicopper oxidase that requires copper for activity. Because it is transported by the twin-arginine translocation (Tat) pathway, which transports folded proteins, a requirement for cofactor assembly before translocation has been discussed. Here we show that CueO is transported as an apo-protein. Periplasmic CueO was readily activated by the addition of copper ions in vitro or under copper stress conditions in vivo Cytoplasmic CueO did not contain copper, even under copper stress conditions. In vitro Tat transport proved that the cofactor assembly was not required for functional Tat transport of CueO. Due to the post-translocational activation of CueO, this enzyme contributes to copper resistance not only by its cuprous oxidase activity but also by chelation of copper ions before they can enter the cytoplasm. Apo-CueO was indistinguishable from holo-CueO in terms of secondary structural elements. Importantly, the binding of copper to apo-CueO greatly stabilized the protein, indicating a transformation from an open or flexible domain arrangement with accessible copper sites to a closed structure with deeply buried copper ions. CueO is thus the first example for a natural Tat substrate of such incomplete folding state. The Tat system may need to transport flexibly folded proteins in any case when cofactor assembly or quaternary structure formation occurs after transport.

Elucidation of the crystal structure of Coriolopsis caperata laccase: restoration of the structure and activity of the native enzyme from the T2-depleted form by copper ions

Laccases are members of a large family of multicopper oxidases that catalyze the oxidation of a wide range of organic and inorganic substrates accompanied by the reduction of dioxygen to water. A new laccase was isolated from the basidiomycete Coriolopsis caperata strain 0677 and its amino-acid sequence was determined. According to its physicochemical properties and spectroscopic features, the laccase from C. caperata is a high redox-potential blue laccase. Attempts to crystallize the native enzyme were unsuccessful. The copper type 2-depleted (T2D) laccase was prepared and crystallized. The structure of T2D laccase from C. caperata was solved at 1.6 Å resolution, and attempts to reconstruct the T2 copper centre were performed using Cu(+) and Cu(2+) ions. The structure of T2D+Cu(+) laccase was solved at 1.89 Å resolution. It was shown that the T2D+Cu(+) laccase structure contained four copper ions in the active site. Reconstruction could not be achieved when the T2D laccase crystals were treated with CuSO4.

Immunoassays of fungal laccases for screening of natural enzymes and control of recombinant enzyme production

Because of the wide application of laccases in different biotechnological processes and intense studies of the enzymes from different sources, the development of efficient techniques for monitoring laccase level is a task of significant importance. Enzyme-linked immunosorbent assay (ELISA) and Western blotting techniques were developed to control total content and isoform composition of laccases, including their recombinant preparations. Because glycosylated and nonglycosylated forms have different structures and sets of epitopes, two kinds of polyclonal antibodies were obtained and applied. The first antibody recognized the native (glycosylated) laccase purified from Trametes hirsuta and the second one reacted with recombinant (nonglycosylated) laccase expressed in Escherichia coli. Titers of the antibodies were analyzed by indirect ELISA with laccases isolated from several strains of basidiomycetes. The obtained cross-reactivity data for both antibodies demonstrated a correspondence with sequence homology of the laccases. The antibodies raised against recombinant (nonglycosylated) laccase had higher titers and thus were preferable for screening of recombinant laccase in cultural media. Thus, optimal antibody preparations were selected for screening of laccase-producing strains, and the control of recombinant enzymes and the efficiency of their use in immunochemical control of laccase levels were confirmed.

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

Copper depletion of bacterial laccases obtained by heterologous expression in Escherichia coli is a common problem in production of these versatile biocatalysts. We demonstrate that coexpression of small soluble copper chaperones can mitigate this problem. The laccase CotA and the copper chaperone CopZ both from Bacillus licheniformis were used as model system. The use of the E. coli BL21(DE3) strain expressing CopZ and CotA simultaneously from two plasmids resulted in an 20% increase in copper occupancy and in 26% higher specific activity. We conclude that not only intracellular copper ion concentration, but also presence of an appropriate copper chaperone influences copper ion insertion into CotA laccase. Moreover, E. coli BL21(DE3) seems to lack such a copper chaperone which can be partially complemented by heterologous expression thereof. The presented system is simple and can routinely be used for improved heterologous production of bacterial laccase in E. coli.

Biochemical studies of the multicopper oxidase (small laccase) from Streptomyces coelicolor using bioactive phytochemicals and site-directed mutagenesis

Multicopper oxidases can act on a broad spectrum of phenolic and non-phenolic compounds. These enzymes include laccases, which are widely distributed in plants and fungi, and were more recently identified in bacteria. Here, we present the results of biochemical and mutational studies of small laccase (SLAC), a multicopper oxidase from Streptomyces coelicolor (SCO6712). In addition to typical laccase substrates, SLAC was tested using phenolic compounds that exhibit antioxidant activity. SLAC showed oxidase activity against 12 of 23 substrates tested, including caffeic acid, ferulic acid, resveratrol, quercetin, morin, kaempferol and myricetin. The kinetic parameters of SLAC were determined for 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid), 2,6-dimethoxyphenol, quercetin, morin and myricetin, and maximum reaction rates were observed with myricetin, where k_cat and K_m values at 60°C were 8.1 (± 0.8) s⁻¹ and 0.9 (± 0.3) mM respectively. SLAC had a broad pH optimum for activity (between pH 4 and 8) and temperature optimum at 60–70°C. It demonstrated remarkable thermostability with a half-life of over 10 h at 80°C and over 7 h at 90°C. Site-directed mutagenesis revealed 17 amino acid residues important for SLAC activity including the 10 His residues involved in copper coordination. Most notably, the Y229A and Y230A mutant proteins showed over 10-fold increase in activity compared with the wild-type SLAC, which was correlated to higher copper incorporation, while kinetic analyses with S929A predicts localization of this residue near the meta-position of aromatic substrates.

Funding Information Funding for this research was provided by the Government of Ontario for the project ‘FFABnet: Functionalized Fibre and Biochemicals’ (ORF-RE-05-005), and the Natural Sciences and Engineering Research Council of Canada.

A multicopper oxidase is required for copper resistance in Mycobacterium tuberculosis

Mycobacterium tuberculosis, the causative agent of tuberculosis, is one of the most important bacterial pathogens. Recent work has revealed that the natural bactericidal properties of copper are utilized by the host immune system to combat infections with bacteria, including M. tuberculosis. However, M. tuberculosis employs multiple mechanisms to reduce the internal copper amount by efflux and sequestration, which are required for virulence of M. tuberculosis. Here, we describe an alternative mechanism of copper resistance by M. tuberculosis. Deletion of the rv0846c gene increased the susceptibility of M. tuberculosis to copper at least 10-fold, establishing Rv0846c as a major component of copper resistance in M. tuberculosis. In vitro assays showed that Rv0846c oxidized organic substrates and Fe(II). Importantly, mutation of the predicted copper-coordinating cysteine 486 resulted in inactive Rv0846c protein which did not protect M. tuberculosis against copper stress. Hence, Rv0846c is a multicopper oxidase of M. tuberculosis and was renamed mycobacterial multicopper oxidase (MmcO). MmcO is membrane associated, probably by lipidation after export across the inner membrane by the twin-arginine translocation system. However, mutation of the lipidation site did not affect the oxidase activity or the copper protective function of MmcO. Our study revealed MmcO as an important copper resistance mechanism of M. tuberculosis, which possibly acts by oxidation of toxic Cu(I) in the periplasm.

Crystal structures of multicopper oxidase CueO bound to copper(I) and silver(I): functional role of a methionine-rich sequence

The multicopper oxidase CueO oxidizes toxic Cu(I) and is required for copper homeostasis in Escherichia coli. Like many proteins involved in copper homeostasis, CueO has a methionine-rich segment that is thought to be critical for copper handling. How such segments function is poorly understood. Here, we report the crystal structure of CueO at 1.1 Å with the 45-residue methionine-rich segment fully resolved, revealing an N-terminal helical segment with methionine residues juxtaposed for Cu(I) ligation and a C-terminal highly mobile segment rich in methionine and histidine residues. We also report structures of CueO with a C500S mutation, which leads to loss of the T1 copper, and CueO with six methionines changed to serine. Soaking C500S CueO crystals with Cu(I), or wild-type CueO crystals with Ag(I), leads to occupancy of three sites, the previously identified substrate-binding site and two new sites along the methionine-rich helix, involving methionines 358, 362, 368, and 376. Mutation of these residues leads to a ∼4-fold reduction in k(cat) for Cu(I) oxidation. Ag(I), which often appears with copper in nature, strongly inhibits CueO oxidase activities in vitro and compromises copper tolerance in vivo, particularly in the absence of the complementary copper efflux cus system. Together, these studies demonstrate a role for the methionine-rich insert of CueO in the binding and oxidation of Cu(I) and highlight the interplay among cue and cus systems in copper and silver homeostasis.

Oxidation of polycyclic aromatic hydrocarbons by the bacterial laccase CueO from E. coli

Laccases produced by white rot fungi are capable of rapidly oxidizing benzo[a]pyrene. We hypothesize that the polycyclic aromatic hydrocarbon (PAH)-degrading bacteria producing laccase can enhance the degree of benzo[a]pyrene mineralization. However, fungal laccases are glycoproteins which cannot be glycosylated in bacteria, and there is no evidence to show that bacterial laccases can oxidize benzo[a]pyrene. In this study, the in vitro oxidation of PAHs by crude preparations of the bacterial laccase, CueO, from Escherichia coli was investigated. The results revealed that the crude CueO catalyzed the oxidation of anthracene and benzo[a]pyrene in the same way as the fungal laccase from Trametes versicolor, but showed specific characteristics such as thermostability and copper dependence. In the presence of 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid), high amounts of anthracene and benzo[a]pyrene, 80% and 97%, respectively, were transformed under optimal conditions of 60°C, pH 5, and 5 mmol l(-1) CuCl(2) after a 24-h incubation period. Other PAHs including fluorene, acenaphthylene, phenanthrene, and benzo[a]anthracene were also oxidized by the crude CueO. These findings indicated the potential application of prokaryotic laccases in enhancing the mineralization of benzo[a]pyrene by PAH-degrading bacteria.

Crystal structure of a two-domain multicopper oxidase: implications for the evolution of multicopper blue proteins

The two-domain multicopper oxidases are proposed to be key intermediates in the evolution of three-domain multicopper oxidases. A number of two-domain multicopper oxidases have been identified from genome sequences and are classified as type A, type B, or type C on the basis of the predicted location of the type 1 copper center. The crystal structure of blue copper oxidase, a type C two-domain multicopper oxidase from Nitrosomonas europaea, has been determined to 1.9 A resolution. Blue copper oxidase is a trimer, of which each subunit comprises two cupredoxin domains. Each subunit houses a type 1 copper site in domain 1 and a type 2/type 3 trinuclear copper cluster at the subunit-subunit interface. The coordination geometry at the trinuclear copper site is consistent with reduction of the copper ions. Although the overall architecture of blue copper oxidase is similar to nitrite reductases, detailed structural alignments show that the fold and domain orientation more closely resemble the three-domain multicopper oxidases. These observations have important implications for the evolution of nitrite reductases and multicopper oxidases.

Copper incorporation into recombinant CotA laccase from Bacillus subtilis: characterization of fully copper loaded enzymes

The copper content of recombinant CotA laccase from Bacillus subtilis produced by Escherichia coli cells is shown to be strongly dependent on the presence of copper and oxygen in the culture media. In copper-supplemented media, a switch from aerobic to microaerobic conditions leads to the synthesis of a recombinant holoenzyme, while the maintenance of aerobic conditions results in the synthesis of a copper-depleted population of proteins. Strikingly, cells grown under microaerobic conditions accumulate up to 80-fold more copper than aerobically grown cells. In vitro copper incorporation into apoenzymes was monitored by optical and electron paramagnetic resonance (EPR) spectroscopy. This analysis reveals that copper incorporation into CotA laccase is a sequential process, with the type 1 copper center being the first to be reconstituted, followed by the type 2 and the type 3 copper centers. The copper reconstitution of holoCotA derivatives depleted in vitro with EDTA results in the complete recovery of the native conformation as monitored by spectroscopic, kinetic and thermal stability analysis. However, the reconstitution of copper to apo forms produced in cultures under aerobic and copper-deficient conditions resulted in incomplete recovery of biochemical properties of the holoenzyme. EPR and resonance Raman data indicate that, presumably, folding in the presence of copper is indispensable for the correct structure of the trinuclear copper-containing site.

A robust metallo-oxidase from the hyperthermophilic bacterium Aquifex aeolicus

The gene, Aquifex aeolicus AAC07157.1, encoding a multicopper oxidase (McoA) and localized in the genome as part of a putative copper-resistance determinant, has been cloned, over-expressed in Escherichia coli and the recombinant enzyme purified to homogeneity. The purified enzyme shows spectroscopic and biochemical characteristics typical of the well-characterized multicopper oxidase family of enzymes. McoA presents higher specificity (k(cat)/K(m)) for cuprous and ferrous ions than for aromatic substrates and is therefore designated as a metallo-oxidase. Addition of copper is required for maximal catalytic efficiency. A comparative model structure of McoA has been constructed and a striking structural feature is the presence of a methionine-rich region (residues 321-363), reminiscent of those found in copper homeostasis proteins. The kinetic properties of a mutant enzyme, McoADeltaP321-V363, deleted in the methionine-rich region, provide evidence for the key role of this region in the modulation of the catalytic mechanism. McoA has an optimal temperature of 75 degrees C and presents remarkable heat stability at 80 and 90 degrees C, with activity lasting for up to 9 and 5 h, respectively. McoA probably contributes to copper and iron homeostasis in A. aeolicus.

Crystal structures of E. coli laccase CueO at different copper concentrations

CueO protein is a hypothetical bacterial laccase and a good laccase candidate for large scale industrial application. Four CueO crystal structures were determined at different copper concentrations. Low copper occupancy in apo-CueO and slow copper reconstitution process in CueO with exogenous copper were demonstrated. These observations well explain the copper dependence of CueO oxidase activity. Structural comparison between CueO and other three fungal laccase proteins indicates that Glu106 in CueO constitutes the primary counter-work for reconstitution of the trinuclear copper site. Mutation of Glu106 to a Phe enhanced CueO oxidation activity and supported this hypothesis. In addition, an extra alpha-helix from Leu351 to Gly378 covers substrate biding pocket of CueO and might compromises the electron transfer from substrate to type I copper.

Expression of laccase gene lcc1 in Coprinopsis cinerea under control of various basidiomycetous promoters

Coprinopsis cinerea laccase gene lcc1 was expressed in this basidiomycete under naturally non-inductive conditions using various homologous and heterologous promoters. Laccase expression was achieved in solid and liquid media with promoter sequences from the C. cinerea tub1 gene, the Agaricus bisporus gpdII gene, the Lentinus edodes priA gene and the Schizophyllum commune Sc3 gene. As measured by enzyme activity in liquid cultures, a 277-bp gpdII promoter fragment, followed by a 423-bp priA fragment, was most efficient. A shorter priA sequence of 372 bp was inactive. tub1 promoter fragments were reasonably active, whereas the S. commune Sc3 promoter sequence was less active, in comparison. Irrespective of the promoter used, addition of copper to the medium increased enzymatic activities for highly active transformants by 10- to 50-fold and for less active transformants for 2- to 7-fold. The highest enzymatic activities (3 U/ml) were reached with the gpdII promoter in the presence of 0.1 mM CuSO(4).