Cloning and heterologous expression of a novel insecticidal gene (tccC1) from Xenorhabdus nematophilus strain

We have identified and cloned a novel toxin gene (tccC1/xptB1) from Xenorhabdus nematophilus strain isolated from Korea-specific entomophagous nematode Steinernema glaseri MK. The DNA sequence of cloned toxin gene (3048 bp) has an open reading frame encoding 1016 amino acids with a predicted molecular mass of 111058 Da. The toxin sequence shares 50-96% identical amino acid residues with the previously reported tccC1 cloned from X. nematophilus, Photorhabdus luminescens W14 P. luminescens TTO1, and Yersinia pestis CO92. The toxin gene was successfully expressed in Escherichia coli, and the recombinant toxin protein caused a rapid cessation in mortality of Galleria mellonella larvae (80% death of larvae within 2 days). Conclusively, the heterologous expression of the novel gene tccC1 cloned into E. coli plasmid vector produced recombinant toxin with high insecticidal activity.     

In vitro anti-influenza virus activity of a cardiotonic glycoside from Adenium obesum (Forssk.)

Methanolic extracts of six Saudi plants were screened for their in vitro antiviral activity using influenza virus A/PR/8/34 (H1N1) and MDCK cells in an MTT assay. The results indicated that the extracts of Adeniumobesum and Tephorosianubica possessed antiviral activity (99.3 and 93.3% inhibition at the concentration of 10 μg/ml, respectively). Based on these results A. obesum was selected for further study by applying bioactivity-guided fractionation to isolate its antiviral principle. The antiviral principle was isolated from the chloroform fraction through solvent fractionation, combined open liquid chromatography and HPLC. The isolated active compound A was identified as oleandrigenin-β-d-glucosyl (1 → 4)-β-d-digitalose, on the basis of its spectral analysis (MS, 1D and 2D NMR). The isolated glycoside showed reduction of virus titre by 69.3% inhibition at concentration of 1 μg/ml (IC₅₀ = 0.86 μg/ml).     

Improvement of cellulase activity in Trichoderma reesei by heterologous expression of a beta-glucosidase gene from Penicillium decumbens

Trichoderma reesei is a well-known cellulase producer and widely applied in enzyme industry. To increase its ability to efficiently decompose cellulose, the beta-glucosidase activity of its enzyme cocktail needs to be enhanced. In this study, a beta-glucosidase I coding sequence from Penicillium decumbens was ligated with the cellobiohydrolase I (cbh1) promoter of T. reesei and introduced into the genome of T. reesei strain Rut-C30 by Agrobacterium-mediated transformation. In comparison to that from the parent strain, the beta-glucosidase activity of the enzyme complexes from two selected transformants increased 6- to 8-fold and their filter paper activity (FPAs) was enhanced by 30% on average. The transformant's saccharifying ability towards pretreated cornstalk was also significantly enhanced. To further confirm the effect of heterologous beta-glucosidase on the cellulase activity of T. reesei, the heterologously expressed pBGL1 was purified and added to the enzyme complex produced by T. reesei Rut-C30. Supplementation of the Rut-C30 enzyme complex with pBGL1 brought about 80% increase of glucose yield during the saccharification of pretreated cornstalk. Our results indicated that the heterologous expression of a beta-glucosidase gene in T. reesei might produce balanced cellulase preparation.     

High-level heterologous expression of fungal cytochrome P450s in Escherichia coli

A thorough understanding of the sequence–structure–function relationships of cytochrome P450 (P450) is necessary to better understand the metabolic diversity of living organisms. Significant amounts of pure enzymes are sometimes required for biochemical studies, and their acquisition often relies on the possibility of their heterologous expression. In this study, we performed extensive heterologous expression of fungal P450s in Escherichia coli using 304 P450 isoforms. Using large-scale screening, we confirmed that at least 27 P450s could be expressed with/without simple sequence deletion at the 5′ end of cDNAs, which encode the N-terminal hydrophobic domain of the enzyme. Moreover, we identified N-terminal amino acid sequences that can potentially be used to construct chimeric P450s, which could dramatically improve their expression levels even when the expression of the wild-type sequence was unpromising. These findings will help increase the chance of heterologous expression of a variety of fungal and other eukaryotic membrane-bound P450s in E. coli.     

Molecular breeding of a novel <Emphasis Type=Italic>Coprinopsis cinerea</Emphasis> strain possessing a heterologous laccase gene, <Emphasis Type=Italic>lccK</Emphasis>, driven by a constitutive promoter

Genomic DNA encoding the Pleurotus ostreatus LccK laccase was fused with the Coprinopsis cinerea β-tubulin promoter and terminator, and introduced into a C. cinerea strain. Linkage analysis, native PAGE separations, substrate specificity investigations and expression profiling indicated that C. cinerea transformants secrete P. ostreatus LccK, suggesting that the introns of the lccK gene are correctly spliced and the signal peptide for secretion is functional in C. cinerea. Transformants constitutively expressing laccase may be useful for the degradation of aromatic compounds.     

Recent advances in discovery,heterologous expression,and molecular engineering of cyclodextrin glycosyltransferase for versatile applications

Cyclodextrin glycosyltransferase (CGTase) is an important enzyme with multiple functions, in particular the production of cyclodextrins. It is also widely applied in baking and carbohydrate glycosylation because it participates in various types of catalytic reactions. New applications are being found with novel CGTases being isolated from various organisms. Heterologous expression is performed for the overproduction of CGTases to meet the requirements of these applications. In addition, various directed evolution techniques have been applied to modify the molecular structure of CGTase for improved performance in industrial applications. In recent years, substantial progress has been made in the heterologous expression and molecular engineering of CGTases. In this review, we systematically summarize the heterologous expression strategies used for enhancing the production of CGTases. We also outline and discuss the molecular engineering approaches used to improve the production, secretion, and properties (e.g., product and substrate specificity, catalytic efficiency, and thermal stability) of CGTase.     

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.     

Incorporation of dengue virus replicon into virus-like particles by a cell line stably expressing precursor membrane and envelope proteins of dengue virus type 2

While virus-like particles (VLPs) containing subgenomic replicons, which can transduce replicons into target cells efficiently for studying viral replication and vectors of gene therapy and vaccine, have been established for several flaviviruses, none has been reported for the four serotypes of dengue virus, the causal agent of the most important arboviral diseases in this century. In this study, we successfully established a cell line stably expressing the precursor membrane/envelope (PrM/E) proteins of dengue virus type 2 (DENV2), which can package a DENV2 replicon with deletion of PrM/E genes and produce single-round infectious VLPs. Moreover, it can package a similar replicon of different serotype, dengue virus type 4, and produce infectious chimeric VLPs. To our knowledge, this study reports for the first time replicon-containing VLPs of dengue virus. Moreover, this convenient system has potential as a valuable tool to study encapsidation of dengue virus and to develop novel chimeric VLPs containing dengue virus replicon as vaccine in the future.     

Construction and heterologous expression of a synthetic copy of the cutinase cDNA from Fusarium solani pisi

A copy of the cutinase cDNA from Fusarium solani pisi was constructed starting from synthetic oligonucleotides. For this construction three separate cassettes were made, which were subsequently assembled to form the cutinase gene. Heterologous expression of the synthetic cutinase gene and the subsequent secretion of the recombinant enzyme was achieved in Saccharomyces cerevisiae and Aspergillus awamori.     

Cloning, sequence analysis and heterologous expression in Pichia pastoris of a gene encoding a thermostable cellobiose dehydrogenase from Myriococcum thermophilum

We cloned and expressed a gene encoding a thermostable cellobiose dehydrogenase (CDH) from the thermophilic ascomycete Myriococcum thermophilum. The 2904 bp long open reading frame contained six introns located either close to the 5′- or 3′-end of the ORF. The corresponding cDNA of 2487 bp was cloned into the expression vector pPICZαB to achieve inducible heterologous expression and secretion of the recombinant flavocytochrome in the methylotrophic yeast Pichia pastoris. Transformants were selected on media with normal and 10-fold increased zeocin concentration, and selected clones were tested for inducible extracellular production of the recombinant oxidoreductase. The maximally obtained volumetric activity was 0.25 U/ml in YPM (rich) medium and 2.15 U/ml in production stage (minimal) medium in a fed-batch fermentation. Recombinant CDH was purified in two consecutive chromatographic steps leading to a final specific activity of up to 7.4 U/mg protein at 40 °C. Kinetic properties of the recombinant CDH were characterized and the temperature optimum for the recombinant CDH was determined at 63 °C. Certain properties of the sequence of MtCDH are discussed in context with thermal and proteolytic stability.     

Expression of A mating type genes of Coprinus cinereus in a heterologous basidiomycete host

The A mating factor of Coprinus cinereus determines compatibility in mating by regulating part of a developmental sequence that leads to dikaryon formation. The A genes that trigger development encode two different classes of homeodomain proteins, and for a successful mating, a protein of one class, HD 1, must interact with a protein of the other class, HD 2. In this report we show that C. cinereus A genes that encode HD 2 proteins, a2-1 and b2-1, can elicit A-regulated development in the heterologous host C. bilanatus. Transformation rates were very low, suggesting that the genes were poorly transcribed. The fact that the HD 2 genes are functionally expressed implies successful heteromultimeric association of putative DNA-binding proteins coded by the two Coprinus species. This interaction was sufficient to satisfy the need for different A factors in the formation of a fertile C. bilanatus dikaryon, but fertile dikaryons were more readily produced in matings with the a2-1 gene transformants. The C. cinereus A genes, b1-1 and d1-1, which encode HD1 proteins, were either not expressed or their proteins were non-functional in C. bilanatus. These experiments raise some interesting questions regarding HD1–HD2 protein interactions.     

Generation of linear expression constructs by one-step PCR with vaccinia DNA topoisomerase I

Linear expression constructs can facilitate gene function studies. We describe a method to generate linear expression constructs for mammalian cells by one-step polymerase chain reaction (PCR) with vaccinia DNA topoisomerase I (TOPO). Cytomegalovirus (CMV) 5′ promoter, the gene of interest, and V5 bovine growth hormone (BGH) polyA 3′ terminator elements were PCR-amplified with target-specific primers containing vaccinia DNA TOPO-specific sequence and complementary sequence to each other. We amplified specific and complementary sequences. These three elements were directionally joined with vaccinia TOPO. The joined products were then directly transfected into Chinese hamster ovary cells. Compared with the transfection of supercoiled plasmids, comparable expression signals were obtained for green fluorescent protein, chloramphenicol acetyltransferase, and β-galactosidase proteins using Western blots. This is a quick and efficient method to generate linear expression construct. Unlike Invitrogen TOPO Tools, our method avoided the secondary round of PCR and more rapidly yielded correct joining products. This method can be easily used in the function test of uncharacterized open reading frames.     

The infectivity and pathogenicity of hepatitis A virus live-attenuated vaccine strain H2 in type I interferon receptor-deficient mice

Hepatitis A virus (HAV) live-attenuated vaccine H2 strain has been approved for clinical use for decades with ideal safety profiles in nonhuman primate models and humans. Recently, type I interferon (IFN) receptor-deficient mice were shown to be susceptible to HAV infection. Herein, we sought to determine the infection and replication dynamics of the H2 in Ifnar^-/- mice that lack type I IFN receptor. Following intravenous injection, the H2 failed to cause obvious clinical symptoms in Ifnar^-/- mice, and no significant upregulation in serum alanine aminotransferase (ALT) levels was observed. Notably, the histopathological examination showed that there were significant focal infiltrations of lymphocytes and neutrophils in the portal area, but no focal necrosis was observed in liver tissues. Viral RNAs sustained in the liver, and the infectious virus could be recovered from the liver tissue until 42 days post-infection. More importantly, H2 infection induced obvious viremia and persistent viral shedding in feces. In addition, robust HAV-specific humoral immune responses were induced in Ifnar^-/- mice. Overall, our study revealed the safety profile of H2 in Ifnar^-/- mice, which not only helps understand the attenuation mechanism of H2, but also expands the application of the Ifnar^-/--/- mouse model for HAV studies.     

Heterologous expression of functionally active enterolysin A, class III bacteriocin from Enterococcus faecalis, in Escherichia coli

The heterologous expression of enterolysin A (EnlA), heat-labile class III bacteriocin from Enterococcus faecalis II/1 with anti-listerial activity, was studied in Escherichia coli. The PCR amplified products of enterolysin A structural gene, N-terminal part of EnlA with endopeptidase-like activity and C-terminal part of EnlA similar to a lysis gene of bacteriophage, were cloned in prelinearized pQE-30UA expression vector. The expression of EnlA structural gene led to the synthesis and secretion of functional-active His-tagged enterolysin A protein, which was purified to homogeneity using His-Select™ Cartridge and was shown to be fully active against the indicator strain. The expression of N-terminal or C-terminal part of EnlA and deletion of last 58 amino acids from C-terminal domain of EnlA led to the synthesis of biologically non-active proteins.     

Systemic induction of proteinase-inhibitor-II gene expression in potato plants by wounding

The systemic induction of expression of the gene for proteinase inhibitor II after wounding different parts of potato (Solanum tuberosum L.) plants was analysed at the RNA level. Wounding of either leaves or tubers led to an induction of expression of this gene in non-wounded upper and lower leaves as well as in the upper stem segment, whereas no expression was observed in nonwounded roots or in the lower stem segment. The signal mediating the systemic induction in nonwounded tissue must therefore be able to move both acropetally and basipetally. The systemic wound response is specific for the expression of the proteinase-inhibitor-II gene as no influence was observed for the expression of genes encoding the small subunit of ribulose-1,5-bisphosphate carboxylase and the tuber storage protein patatin which were examined in parallel with the proteinase-inhibitor-II gene.Abbreviation ssRubisco small subunit of ribulose-1,5-bis-phosphate carboxylase     

Improved production of erythromycin A by expression of a heterologous gene encoding S-adenosylmethionine synthetase

An S-adenosylmethionine synthetase (SAM-s) gene from Streptomyces spectabilis was integrated along with vector DNA into the chromosome of a Saccharopolyspora erythraea E2. Elevated production of SAM was observed in the recombinant strain Saccharopolyspora erythraea E1. The results from the bioassay showed that the titer of erythromycin was increased from 920 IU ml⁻¹ by E₂ to approximately 2,000 IU ml⁻¹ by E₁. High performance liquid chromatography (HPLC) analysis revealed that there was a 132% increase in erythromycin A compared with the original strain, while the erythromycin B, the main impurity component in erythromycin, was decreased by 30%. The sporulation process was inhibited, while the SAM-s gene was expressed. The addition of the exogenous SAM also inhibited sporulation and promoted an increase in erythromycin titers. An erratum to this article can be found at     

Ultraviolet B and A irradiation induces fibromodulin expression in human fibroblasts in vitro

Ultraviolet (UV) radiation affects the extracellular matrix (ECM) of the human skin. The small leucine-rich repeat protein fibromodulin interacts with type I and II collagen fibrils, thereby affecting ECM assembly. The aim of this study was to evaluate whether short wave UV (UVB) or long wave UV (UVA) irradiation influences fibromodulin expression. Exponentially growing human fibroblasts (IMR-90 cells) were exposed to increasing doses of UVB (2.5–60 mJ/cm²) or UVA (0.5–10 J/cm²). After UV irradiation fibromodulin, p21 and GADD45 levels were evaluated as well as cell viability, reactive oxygen species formation (ROS) and DNA damage. We found that fibromodulin expression: (i) increased after UVB and UVA irradiation; (ii) was 10-fold higher after UVA (10 J/cm²) versus 5-fold with UVB (10 mJ/cm²); (iii) correlated with reactive oxygen species formation, particularly after UVA; and (iv) was linked to the DNA damage binding protein (DDB1) translocation in the nucleus, particularly after UVB. These results further suggest that the UV-induced fibromodulin increase could counteract the UV-induced connective tissue damage, promoting the assembly of new collagen fibrils.