The role of intracellular β-glucosidase in cellulolytic response induction in filamentous fungus Penicillium verruculosum

In this study, CRISPR/Cas9 genome editing was used to knockout the bgl2 gene encoding intracellular β-glucosidase filamentous fungus Penicillium verruculosum. This resulted in a dramatic reduction of secretion of cellulolytic enzymes. The study of P. verruculosum Δbgl2 found that the transcription of the cbh1 gene, which encodes cellobiohydrolase 1, was impaired when induced by cellobiose and cellotriose. However, the transcription of the cbh1 gene remains at level of the host strain when induced by gentiobiose. This implies that gentiobiose is the true inducer of the cellulolytic response in P. verruculosum, in contrast to Neurospora crassa where cellobiose acts as an inducer.

Expression and Refolding of the Plant Chitinase From Drosera capensis for Applications as a Sustainable and Integrated Pest Management

Recently, the study of chitinases has become an important target of numerous research projects due to their potential for applications, such as biocontrol pest agents. Plant chitinases from carnivorous plants of the genus Drosera are most aggressive against a wide range of phytopathogens. However, low solubility or insolubility of the target protein hampered application of chitinases as biofungicides. To obtain plant chitinase from carnivorous plants of the genus Drosera in soluble form in E.coli expression strains, three different approaches including dialysis, rapid dilution, and refolding on Ni-NTA agarose to renaturation were tested. The developed « Rapid dilution » protocol with renaturation buffer supplemented by 10% glycerol and 2M arginine in combination with the redox pair of reduced/oxidized glutathione, increased the yield of active soluble protein to 9.5 mg per 1 g of wet biomass. A structure-based removal of free cysteines in the core domain based on homology modeling of the structure was carried out in order to improve the soluble of chitinase. One improved chitinase variant (C191A/C231S/C286T) was identified which shows improved expression and solubility in E. coli expression systems compared to wild type. Computational analyzes of the wild-type and the improved variant revealed overall higher fluctuations of the structure while maintaining a global protein stability. It was shown that free cysteines on the surface of the protein globule which are not involved in the formation of inner disulfide bonds contribute to the insolubility of chitinase from Drosera capensis. The functional characteristics showed that chitinase exhibits high activity against colloidal chitin (360 units/g) and high fungicidal properties of recombinant chitinases against Parastagonospora nodorum. Latter highlights the application of chitinase from D. capensis as a promising enzyme for the control of fungal pathogens in agriculture.

Evolutionary Relationships Between the Laccase Genes of Polyporales: Orthology-Based Classification of Laccase Isozymes and Functional Insight From Trametes hirsuta

Laccase is one of the oldest known and intensively studied fungal enzymes capable of oxidizing recalcitrant lignin-resembling phenolic compounds. It is currently well established that fungal genomes almost always contain several non-allelic copies of laccase genes (laccase multigene families); nevertheless, many aspects of laccase multigenicity, for example, their precise biological functions or evolutionary relationships, are mostly unknown. Here, we present a detailed evolutionary analysis of the sensu stricto laccase genes (CAZy - AA1_1) from fungi of the Polyporales order. The conducted analysis provides a better understanding of the Polyporales laccase multigenicity and allows for the systemization of the individual features of different laccase isozymes. In addition, we provide a comparison of the biochemical and catalytic properties of the four laccase isozymes from Trametes hirsuta and suggest their functional diversification within the multigene family.

[Engineering of a System for the Production of Mutant Human Alpha-Fetoprotein in the Methylotrophic Yeast Pichia pastoris]

A system for the production of mutant recombinant human alpha-fetoprotein (rhAFPO) lacking the glycosylation site has been engineered in the yeast Pichia pastoris. A strain of the methylotrophic yeast Pichia pastoris GS 115/pPICZ?A/rhAFP0, which produces unglycosylated rhAFPO and secretes it to the culture medium, has been constructed. Optimization and scale-up of the fermentation technology have resulted in an increase in the rhAFP0 yield to 20 mg/L. A scheme of isolation and purification of biologically active rhAFP0 has been developed. The synthesized protein has the antitumor activity, which is analogous to the activity of natural human embryonic alpha-fetoprotein.

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.

[The mutational analysis of carbon catabolite repression in filamentous fungus Penicillium canescens]

Penicillium canescens strain F178 is a natural producer of beta-galactosidase and endo-1,4-beta-xylanase. The transcription of genes bgaS and xylA, coding for these proteins, is subject to carbon catabolite repression. The system for selective isolation of regulatory mutants in P. canescens is developed. Two strains from the mutant collection are studied in details. It is shown that both mutations can be complement by creA gene of P. canescens, encoding global regulator of carbon catabolite repression in filamentous fungi. creA(-) alleles contain frameshift mutations in C-domain of CreA. Gene xylA is derepressed in mutants at transcription level in the presence of D-glucose. A transcription of creA gene in mutants is also derepressed proving effect of autoregulation for this gene.

[Multigene families of endo-(1-4)-beta-xylanases of Penicillium canescens]

Four novel genes of the enzymes of the endoxylanase (EC 3.2.1.8) families found in the mycelial fungus Penicillium canescens have been cloned. The xylB, xylC, and xylD genes encode endoxylanases of glycosyl hydrolase family 11; the xylEgene, those of family 10. In the promoter region of the xylB, xylC, and xylD genes, the binding sequences for the protein activator of xylanolytic gene transcription have been found; the promoter region of the xylB gene contains the binding sequences for the catabolite repression protein. Since the TATAA sequence, which is an element of the minimal eukaryotic promoter, has not been found in the promoter region of the xylC gene, in contrast to those of the xylB and xylD genes, it may be assumed that this gene is silent. Comparative phylogenetic analysis has shown that the cloned genes are highly homologous to some endoxylanase genes of mycelial fungi of the genera Penicillium and Aspergillus. However, within the species P. canescens, they exhibit a low homology both within and between families, and they diverge into different branches of the phylogenetic tree, which suggest divergence of the genes of this group at an early stage of evolution.

[Transcriptional regulator of carbon catabolite repression CreA in filamentous fungus]

Penicillium canescens strain F178 is a natural producer of beta-galactosidase and endo-1,4-beta-xylanase. Tanscription of genes bgaS and xylA coding for these proteins is subject to carbon catabolite repression which proceed mainly in filamentous fungi by transcriptional repressor CreA. creA gene of P. canescens was cloned. It was demonstrated that creA transcription is also subject to carbon catabolite repression. CreA protein remains intranuclear independently of nature of carbon source and glucose concentration in culture medium. In vitro experiments confirm availability of four CreA-binding sites in bgaS promoter, four sites in xylA promoter and one such site in creA promoter.

[A heterologous production of the Trametes hirsuta laccase in the fungus Penicillium canescens]

A heterologous protein expression in the fungus Penicillium canescens is described for the first time. The fungal strains producing Trametes hirsuta laccase under control of a highly efficient promoter of the P. canescens gene bgaS has been constructed. These strains efficiently transcribe the T. hirsuta 072 laccase gene with a correct intron splicing. Activity of the secreted heterologous laccase in the culture liquid reaches 3 U/ml, accounting for 98% of the total laccase activity, which demonstrates a high efficiency ofheterologous secretion. The synthesized P. canescens laccase has the same molecular weight as the enzyme produced by T. hirsuta 072.

Regulatory activity of heterologous gene-activator xlnR of Aspergillus niger in Penicillium canescens

The gene encoding the xlnR xylanolytic activator of the heterologous fungus Aspergillus niger was incorporated into the Penicillium canescens genome. Integration of the xlnR gene resulted in the increase in a number of activities, i.e. endoxylanase, beta-xylosidase, alpha-L-arabinofuranosidase, alpha-galactosidase, and feruloyl esterase, compared to the host P. canescens PCA 10 strain, while beta-galactosidase, beta-glucosidase, endoglucanase, and CMCase activities remained constant. Two different expression constructs were developed. The first consisted of the nucleotide sequence containing the mature P. canescens phytase gene under control of the axhA promoter region gene encoding A. niger (1,4)-beta-D-arabinoxylan-arabinofuranohydrolase. The second construct combined the P. canescens phytase gene and the bgaS promoter region encoding homologous beta-galactosidase. Both expression cassettes were transformed into P. canescens host strain containing xlnR. Phytase synthesis was observed only for strains with the bgaS promoter on arabinose-containing culture media. In conclusion, the bgaS and axhA promoters were regulated by different inducers and activators in the P. canescens strain containing a structural tandem of the axhA promoter and the gene of the xlnR xylanolytic activator.

[Cloning of the Penicillium canescens endo-1,4-beta-glucanase gene egl3 and the characterization of the recombinant enzyme]

The gene egl3 of the filamentous fungus Penicillium canescens endo-1,4-beta-glucanase, belonging to family 12 glycosyl hydrolases, was cloned and sequenced. The gene was expressed in P. canescens under the control of the strong promoter of gene bgaS, coding for beta-galactosidase of this fungus, and efficient endoglucanase producer strains were obtained. The recombinant protein was isolated from the culture liquid of the producer strain EGL3-13 and purified to homogeneity; its specific activity was 31.7 IU; molecular weight, 26 kDa; and pH and temperature optimums, 3.2 and 54 degrees C, respectively. The Km and Vm values for CMC hydrolysis were determined; they amounted to 17.1 g/1 and 0.31 microM/(mg s), respectively.

Isolation and characterization of extracellular alpha-galactosidases from Penicillium canescens

Two alpha-galactosidases were purified to homogeneity from the enzymatic complex of the mycelial fungus Penicillium canescens using chromatography on different sorbents. Substrate specificity, pH- and temperature optima of activity, stability under different pH and temperature conditions, and the influence of effectors on the catalytic properties of both enzymes were investigated. Genes aglA and aglC encoding alpha-galactosidases from P. canescens were isolated, and amino acid sequences of the proteins were predicted. In vitro feed testing (with soybean meal and soybean byproducts enriched with galactooligosaccharides as substrates) demonstrated that both alpha-galactosidases from P. canescens could be successfully used as feed additives. alpha-Galactosidase A belonging to the 27th glycosyl hydrolase family hydrolyzed galactopolysaccharides (galactomannans) and alpha-galactosidase C belonging to the 36th glycosyl hydrolase family hydrolyzed galactooligosaccharides (stachyose, raffinose, etc.) of soybean with good efficiency, thus improving the digestibility of fodder.

Isolation and characterization of extracellular pectin lyase from Penicillium canescens

Pectin lyase A (molecular weight 38 kD by SDS-PAGE, pI 6.7) was purified to homogeneity from culture broth of the mycelial fungus Penicillium canescens using chromatographic techniques. During genomic library screening, the gene encoding pectin lyase A from P. canescens (pelA) was isolated and sequenced, and the amino acid sequence was generated by applying the multiple alignment procedure (360 residues). A theoretical model for the three dimensional structure of the protein molecule was also proposed. Different properties of pectin lyase A were investigated: substrate specificity, pH- and temperature optimum of activity, stability under different pH and temperature conditions, and the effect of Ca2+ on enzyme activity. In the course of the laboratory trials, it was demonstrated that pectin lyase A from P. canescens could be successfully applied to production and clarification of juice.

[Cloning of an endo-1,4-beta-xylanase gene from Penicillium canescens and construction of multicopy strains]

The complete gene xylA that encodes endo-1,4-beta-xylanase secreted by Penicillium canescens was cloned and sequenced. The coding region of the gene is separated by eight introns. The protein comprises 302 amino acids of the mature protein and 25 amino acids of the signal peptide. The xylanase of P. canescens belongs to the glycosyl hydrolase family 10. Nucleotide sequences for binding catabolite repression protein CREA and transactivator protein were detected in the promoter region. A set of multicopy strains displaying a seven-eightfold increase in xylanase yield was obtained. The fraction of xylanase in most productive strains amounted to 30-50% of the total secreted protein.