Expression of endo-1, 4-beta-xylanase from Trichoderma reesei in Pichia pastoris and functional characterization of the produced enzyme

Temperature-dependent structural changes in xylanase II from Trichoderma longibrachiatum

Endo-β-1,4-xylanases degrade heteroxylans that constitute the lignocellulosic plant cell wall. This enzyme is widely used in the food, paper, textile, and biorefinery industries. Temperature affects the optimum activity of xylanase and is an important factor in its application. Various structural analyses of xylanase have been performed, but its structural influence by temperature is not fully elucidated. To better understand the structural influence of xylanase due to temperature, the crystal structure of xylanase II from Trichoderma longibrachiatum (TloXynII) at room and cryogenic temperatures was determined at 2.1 and 1.9 Å resolution, respectively. The room-temperature structure of TloXynII (TloXynIIRT) showed a B-factor value 2.09 times higher than that of the cryogenic-temperature structure of TloXynII (TloXynIICryo). Subtle movement of the catalytic and substrate binding residues was observed between TloXynIIRT and TloXynIICryo. In TloXynIIRT, the thumb domain exhibited high flexibility, whereas in TloXynIICryo, the finger domain exhibited high flexibility. The substrate binding cleft of TloXynIIRT was narrower than that of TloXynIICryo, indicating a distinct finger domain conformation. Numerous water molecule networks were observed in the substrate binding cleft of TloXynIICryo, whereas only a few water molecules were observed in TloXynIIRT. These structural analyses expand our understanding of the temperature-dependent conformational changes in xylanase.

Advances in Komagataella phaffii Engineering for the Production of Renewable Chemicals and Proteins

The need for a more sustainable society has prompted the development of bio-based processes to produce fuels, chemicals, and materials in substitution for fossil-based ones. In this context, microorganisms have been employed to convert renewable carbon sources into various products. The methylotrophic yeast Komagataella phaffii has been extensively used in the production of heterologous proteins. More recently, it has been explored as a host organism to produce various chemicals through new metabolic engineering and synthetic biology tools. This review first summarizes Komagataella taxonomy and diversity and then highlights the recent approaches in cell engineering to produce renewable chemicals and proteins. Finally, strategies to optimize and develop new fermentative processes using K. phaffii as a cell factory are presented and discussed. The yeast K. phaffii shows an outstanding performance for renewable chemicals and protein production due to its ability to metabolize different carbon sources and the availability of engineering tools. Indeed, it has been employed in producing alcohols, carboxylic acids, proteins, and other compounds using different carbon sources, including glycerol, glucose, xylose, methanol, and even CO2.

Molecular and Biochemical Analyses of a Novel Trifunctional Endoxylanase/Endoglucanase/Feruloyl Esterase from the Human Colonic Bacterium Bacteroides intestinalis DSM 17393

A novel enzyme Bi76 comprising GH10, E_set_Esterase_N, and CE1 modules was identified, with the highest homology (62.9%) with a bifunctional endoxylanase/feruloyl esterase among characterized enzymes. Interestingly, Bi76 hydrolyzed glucan substrates besides xylans and feruloylated substrates, suggesting that it is the first characterized trifunctional endoxylanase/endoglucanase/feruloyl esterase. Analyses of truncation variants revealed that GH10 and E_set_Esterase_N + CE1 modules encoded endoxylanase/endoglucanase and feruloyl esterase activities, respectively. Synergism analyses indicated that endoxylanase, α-l-arabinofuranosidase, and feruloyl esterase acted cooperatively in releasing ferulic acid (FA) and xylooligosaccharides from feruloylated arabinoxylan. The interdomain synergism of Bi76 overmatched the intermolecular synergism of TM1 and TM2. Importantly, Bi76 exhibited good capacity in producing FA, releasing 5.20, 4.38, 2.12, 1.35, 0.46, and 0.19 mg/g from corn bran, corn cob, wheat bran, corn stover, rice husk, and rice bran, respectively. This study expands the trifunctional endoxylanase/endoglucanase/feruloyl esterase repertoire and demonstrates the great potential of Bi76 in agricultural residue utilization.

Cloning and Heterologous Expression of a Novel Xylanase Gene TAX1 from Trichoderma atroviride and Its Application in the Deconstruction of Corn Stover

Xylanase plays a vital role in the efficient utilization of xylan, which accounts for up to 30% of plant dry matter. However, the production cost of xylanase remains high, and the enzymatic characteristics of xylanases of most microorganisms are not suitable for industrial production. Therefore, it is of great significance to discover and develop new and efficient xylanases. In this study, the xylanase gene TAX1 (672 bp cDNA) was cloned from Trichoderma atroviride 3.3013 and expressed in Pichia pastoris. The TAX1 gene encoded a 223-amino acid protein (TAX1) with a molecular weight of 24.2 kDa which showed high similarity to glycoside hydrolase family 11. Enzyme activity assay verified that the recombinant xylanase TAX1 had optimal activity (215.3 IU/mL) at 50°C and pH 6.0. Stable working conditions were measured as pH 4.0-7.0 and 40-60°C. By adding Zn2+, the relative enzymatic activity of recombinant TAX1 was enhanced by 26%. The recombinant xylanase showed high activity toward birchwood xylan and corn stover. The Km and Kcat for xylan and corn stover were 0.36 mg/mL and 0.204 S-1 and 0.48 mg/mL and 0.149 S-1, respectively. The enzymatic activity of the TAX1 produced by P. pastoris was about 2.4-4 times higher that directly isolated from T. atroviride, so engineered P. pastoris for xylanase production could be an ideal candidate for industrial enzyme production.

Effect of the single mutation N9Y on the catalytical properties of xylanase Xyn11A from Cellulomonas uda: a biochemical and molecular dynamic simulation analysis

Cellulomonas uda produces Xyn11A, moderately thermostable xylanase, with optimal activity at 50 °C and pH 6.5. An improvement in the biochemical properties of Xyn11A was achieved by site-directed mutagenesis approach. Wild-type xylanase, Xyn11A-WT, and its mutant Xyn11A-N9Y were expressed in Escherichia coli, and then both enzymes were purified and characterized. Xyn11A-N9Y displayed optimal activity at 60 °C and pH 7.5, an upward shift of 10 ºC in the optimum temperature, and an upward shift of one unit in optimum pH; also, it manifested an 11-fold increase in thermal stability at 60 ºC, compared to that displayed by Xyn11A-WT. Molecular dynamics (MD) simulations of Xyn11A-WT and Xyn11A-N9Y suggest the substitution N9Y leads to an array of secondary structure changes at the N-terminal end and an increase in the number of hydrogen bonds in Xyn11A-N9Y. Based on the significant improvements, Xyn11A-N9Y may be considered as a candidate for several biotechnological applications.

Cloning, characterization and expression of a gene encoding endo-1, 4- β-xylanase from the fungus Termitomyces clypeatus

Enzymatic degradation of hemi-cellulosic substrates has gained plenty of industrial attentions recently. Complete enzymatic degradation of complex and recalcitrant hemicellulose requires an enzymatic cocktail consisting primarily of endo-1,4-β-xylanase (xyl), β-xylosidase, arabinofuranosidase etc. This article reports, for the first time, the identification, cloning, expression and partial characterization of a potent endo-1,4- β-xylanase gene (pxyl) from the mushroom Termitomyces clypeatus (TC) in E. coli and S. cerevisiae. The cDNA for pxyl was found to be 678 bp that in turn gives rise to a precursor protein (Pxyl) of 225 amino acids long when cloned in prokaryotic expression vector. To characterize additionally, the cDNA was also expressed in S. cerevisiae. Bioinformatics study predicted that the Pxyl contains a 19 amino acid long leader peptide that enables post translational modifications including glycosylation as well as its efficient secretion in the medium. The recombinant protein has been found to be a member of GH11 family containing two distant glutamic acids as catalytic residues. This report describes yet another new and potent source of xylanase for commercial exploitation by industry in future.

Multicomponent carbohydrase system from Trichoderma reesei: A toolbox to address complexity of cell walls of plant substrates in animal feed

A diverse range of monocot and dicot grains and their by-products are commonly used in the animal feed industry. They all come with complex and variable cell wall structures which in turn contribute significant fiber to the complete feed. The cell wall is a highly interconnected matrix of various polysaccharides, proteins and lignin and, as such, requires a collaborative effort of different enzymes for its degradation. In this regard, we investigated the potential of a commercial multicomponent carbohydrase product from a wild type fermentation of Trichoderma reesei (T. reesei) (RONOZYME® MultiGrain) in degrading cell wall components of wheat, barley, rye, de-oiled rice bran, sunflower, rapeseed and cassava. A total of thirty-one different enzyme proteins were identified in the T. Reesei carbohydrase product using liquid chromatography with tandem mass spectrometry LC-MS/MS including glycosyl hydrolases and carbohydrate esterases. As measured by in vitro incubations and non-starch polysaccharide component analysis, and visualization by immunocytochemistry and confocal microscopy imaging of immuno-labeled samples with confocal microscopy, the carbohydrase product effectively solubilized cellulolytic and hemicellulolytic polysaccharides present in the cell walls of all the feed ingredients evaluated. The T. reesei fermentation also decreased viscosity of arabinoxylan, xyloglucan, galactomannan and β-glucan substrates. Combination of several debranching enzymes including arabinofuranosidase, xylosidase, α-galactosidase, acetyl xylan esterase, and 4-O-methyl-glucuronoyl methylesterase with both GH10 and GH11 xylanases in the carbohydrase product resulted in effective hydrolyzation of heavily branched glucuronoarabinoxylans. The different β-glucanases (both endo-β-1,3(4)-glucanase and endo-β-1,3-glucanase), cellulases and a β-glucosidase in the T. reesei fermentation effectively reduced polymerization of both β-glucans and cellulose polysaccharides of viscous cereals grains (wheat, barley, rye and oat). Interestingly, the secretome of T. reesei contained significant amounts of an exceptional direct chain-cutting enzyme from the GH74 family (Cel74A, xyloglucan-specific β-1,4-endoglucanase), that strictly cleaves the xyloglucan backbone at the substituted regions. Here, we demonstrated that the balance of enzymes present in the T. reesei secretome is capable of degrading various cell wall components in both monocot and dicot plant raw material used as animal feed.

Aspergillus sydowii: Genome Analysis and Characterization of Two Heterologous Expressed, Non-redundant Xylanases

A prerequisite for the transition toward a biobased economy is the identification and development of efficient enzymes for the usage of renewable resources as raw material. Therefore, different xylanolytic enzymes are important for efficient enzymatic hydrolysis of xylan-heteropolymers. A powerful tool to overcome the limited enzymatic toolbox lies in exhausting the potential of unexplored habitats. By screening a Vietnamese fungal culture collection of 295 undiscovered fungal isolates, 12 highly active xylan degraders were identified. One of the best xylanase producing strains proved to be an Aspergillus sydowii strain from shrimp shell (Fsh102), showing a specific activity of 0.6 U/mg. Illumina dye sequencing was used to identify our Fsh102 strain and determine differences to the A. sydowii CBS 593.65 reference strain. With activity based in-gel zymography and subsequent mass spectrometric identification, three potential proteins responsible for xylan degradation were identified. Two of these proteins were cloned from the cDNA and, furthermore, expressed heterologously in Escherichia coli and characterized. Both xylanases, were entirely different from each other, including glycoside hydrolases (GH) families, folds, substrate specificity, and inhibition patterns. The specific enzyme activity applying 0.1% birch xylan of both purified enzymes were determined with 181.1 ± 37.8 or 121.5 ± 10.9 U/mg for xylanase I and xylanase II, respectively. Xylanase I belongs to the GH11 family, while xylanase II is member of the GH10 family. Both enzymes showed typical endo-xylanase activity, the main products of xylanase I are xylobiose, xylotriose, and xylohexose, while xylobiose, xylotriose, and xylopentose are formed by xylanase II. Additionally, xylanase II showed remarkable activity toward xylotriose. Xylanase I is stable when stored up to 30°C and pH value of 9, while xylanase II started to lose significant activity stored at pH 9 after exceeding 3 days of storage. Xylanase II displayed about 40% activity when stored at 50°C for 24 h. The enzymes are tolerant toward mesophilic temperatures, while acting in a broad pH range. With site directed mutagenesis, the active site residues in both enzymes were confirmed. The presented activity and stability justify the classification of both xylanases as highly interesting for further development.

Exploiting xylan as sugar donor for the synthesis of an antiproliferative xyloside using an enzyme cascade

BACKGROUND

Currently, industrial societies are seeking for green alternatives to conventional chemical synthesis. This demand has merged with the efforts to convert lignocellulosic biomass into value-added products. In this context, xylan, as one of main components of lignocellulose, has emerged as a raw material with high potential for advancing towards a sustainable economy.

RESULTS

In this study, the recombinant endoxylanase rXynM from the ascomycete Talaromyces amestolkiae has been heterologously expressed in Pichia pastoris and used as one of the catalysts of an enzyme cascade developed to synthesize the antiproliferative 2-(6-hydroxynaphthyl) β-D-xylopyranoside, by transglycosylation of 2,6-dihydroxynaphthalene. The approach combines the use of two fungal xylanolytic enzymes, rXynM and the β-xylosidase rBxTW1 from the same fungus, with the cost-effective substrate xylan. The reaction conditions for the cascade were optimized by a Central Composite Design. Maximal productions of 0.59 and 0.38 g/L were reached using beechwood xylan and birchwood xylan, respectively. For comparison, xylans from other sources were tested in the same reaction, suggesting that a specific optimization is required for each xylan variety. The results obtained using this enzyme cascade and xylan were similar or better to those previously reported for a single catalyst and xylobiose, an expensive sugar donor.

CONCLUSIONS

Beechwood and birchwood xylan, two polysaccharides easily available from biomass, were used in a novel enzyme cascade to synthetize an antiproliferative agent. The approach represents a green alternative to the conventional chemical synthesis of 2-(6-hydroxynaphthyl) β-D-xylopyranoside using a cost-effective substrate. The work highlights the role of xylan as a raw material for producing value-added products and the potential of fungal xylanolytic enzymes in the biomass conversion.

Efficient Expression of Xylanase by Codon Optimization and Its Effects on the Growth Performance and Carcass Characteristics of Broiler

Simple Summary

The aim of this work was to combine xylanase expression and broiler production. The xylanase (XynB) gene from Trichoderma reesei was optimized to increase its expression level in Pichia pastoris. The maximum activity of xylanase (optiXynB) secreted by P. pastoris pPICZaA-optiXynB was 1299 U/mL after 96 h induction. The recombinase was highly specific towards birchwood xylan, beechwood xylan, and oat-spelt xylan. Dietary 1000 and 1500 IU/kg optiXynB significantly increased (p < 0.05) final weight and body weight gain; dietary 500, 1000, and 1500 IU/kg optiXynB significantly increased (p < 0.05) pre-evisceration weight, dressed percentage, and eviscerated weight compared with the control group. Results suggested that the optiXynB from P. pastoris pPICZaA-optiXynB has great application in broiler production.

Abstract

The aim of the present study was to improve the expression level of Trichoderma reesei xylanase (XynB) in Pichia pastoris through a codon optimization strategy and evaluate its effects on the growth performance and carcass characteristics of broiler. According to the codon bias of Pichia genome, the XynB gene from T. reesei was optimized and synthesized by whole gene assembly to improve its expression level in P. pastoris. Approximately 180 target mutations were successfully introduced into natural XynB. The maximum activity of xylanase (optiXynB) secreted by P. pastoris pPICZaA-optiXynB was 1299 U/mL after 96 h induction. Purified recombinant optiXynB had the molecular weight of 24 kDa. The optiXynB presented highest activity in pH 5.0 and 50 °C. The recombinase was highly specific towards birchwood xylan, beechwood xylan, and oat-spelt xylan. In the broiler experiment, a total of 200 Arbor Acre broilers (one day old) were randomly allocated into four groups fed with basal diets containing 0 (control group), 500, 1000, and 1500 IU/kg optiXynB. Dietary 1000 and 1500 IU/kg optiXynB significantly increased (p < 0.05) final weight and body weight gain; dietary 500, 1000, and 1500 IU/kg optiXynB significantly increased (p < 0.05) pre-evisceration weight, dressed percentage, and eviscerated weight compared with the control group. Inclusion of optiXynB in broiler diets linearly increased final weight, body weight gain, breast muscle weight and leg muscle weight, but linearly decreased feed conversion rate (p < 0.05). Furthermore, inclusion of optiXynB in broiler diets linearly and quadratically increased pre-evisceration weight, dressed percentage, and eviscerated weight (p < 0.05). The recombinant optiXynB from P. pastoris pPICZaA-optiXynB was beneficial in improving growth performance and carcass characteristics of broilers.

Characterization of novel lignocellulose-degrading enzymes from the porcupine microbiome using synthetic metagenomics

Plant cell walls are composed of cellulose, hemicellulose, and lignin, collectively known as lignocellulose. Microorganisms degrade lignocellulose to liberate sugars to meet metabolic demands. Using a metagenomic sequencing approach, we previously demonstrated that the microbiome of the North American porcupine (Erethizon dorsatum) is replete with genes that could encode lignocellulose-degrading enzymes. Here, we report the identification, synthesis and partial characterization of four novel genes from the porcupine microbiome encoding putative lignocellulose-degrading enzymes: β-glucosidase, α-L-arabinofuranosidase, β-xylosidase, and endo-1,4-β-xylanase. These genes were identified via conserved catalytic domains associated with cellulose- and hemicellulose-degradation. Phylogenetic trees were created for each of these putative enzymes to depict genetic relatedness to known enzymes. Candidate genes were synthesized and cloned into plasmid expression vectors for inducible protein expression and secretion. The putative β-glucosidase fusion protein was efficiently secreted but did not permit Escherichia coli (E. coli) to use cellobiose as a sole carbon source, nor did the affinity purified enzyme cleave p-Nitrophenyl β-D-glucopyranoside (p-NPG) substrate in vitro over a range of physiological pH levels (pH 5–7). The putative hemicellulose-degrading β-xylosidase and α-L-arabinofuranosidase enzymes also lacked in vitro enzyme activity, but the affinity purified endo-1,4-β-xylanase protein cleaved a 6-chloro-4-methylumbelliferyl xylobioside substrate in acidic and neutral conditions, with maximal activity at pH 7. At this optimal pH, K_M, V_max, and k_cat were determined to be 32.005 ± 4.72 μM, 1.16x10^-5 ± 3.55x10^-7 M/s, and 94.72 s^-1, respectively. Thus, our pipeline enabled successful identification and characterization of a novel hemicellulose-degrading enzyme from the porcupine microbiome. Progress towards the goal of introducing a complete lignocellulose-degradation pathway into E. coli will be accelerated by combining synthetic metagenomic approaches with functional metagenomic library screening, which can identify novel enzymes unrelated to those found in available databases.

Taxonomic identification of the thermotolerant and fast-growing fungus Lichtheimia ramosa H71D and biochemical characterization of the thermophilic xylanase LrXynA

The zygomycete fungus Lichtheimia ramosa H71D, isolated from sugarcane bagasse compost, was identified by applying phylogenetic analysis based on the DNA sequence of the Internal Transcribed Spacer (ITS), and subsequent secondary structure analysis of ITS2. L. ramosa H71D was able to grow over a wide range of temperatures (25–45 °C), manifesting optimal growth at 37 °C. A 64 kDa xylanase (named LrXynA) was purified from the culture supernatant of L. ramosa H71D grown on 2% carboxymethylcellulose (CMC), as the only carbon source. LrXynA displayed optimal activity at pH 6 and temperature of 65 °C. The enzyme retained more than 50% of its maximal activity over a broad range of pH values (4.5–7.5). Enzyme half-life (t_½) times at 55, 65 and 75 °C were 80, 25, and 8 min, respectively. LrXynA showed higher affinity (k_M of 2.87 mg/mL) and catalytic efficiency (k_cat/k_M of 0.651 mg s/mL) towards Beechwood xylan in comparison to other substrates such as Birchwood xylan, Oat-spelt xylan, CMC, Avicel and Solka floc. The predominant final products from LrXynA-mediated hydrolysis of Beechwood xylan were xylobiose and xylotriose, suggesting that the enzyme is an endo-β-1,4 xylanase. Scanning electron microscopy (SEM) imaging of sugar cane bagasse (SCB) treated with LrXynA, alone or in combination with commercial cellulases, showed a positive effect on the hydrolysis of SCB. To our knowledge, this is the first report focusing on the biochemical and functional characterization of an endo-β-1,4 xylanase from the thermotolerant and fast-growing fungus Lichtheimia ramosa.

Expression, Docking, and Molecular Dynamics of Endo-β-1,4-xylanase I Gene of Trichoderma virens in Pichia stipitis

It is essential that major carbohydrate polymers in the lignocellulosic biomass are converted into fermentable sugars for the economical production of energy. Xylan, the major component of hemicelluloses, is the second most naturally abundant carbohydrate polymer comprising 20-40% of the total biomass. Endoxylanase (EXN) hydrolyzes xylan into mixtures of xylooligosaccharides. The objective of this study was to genetically modify Pichia stipitis, a pentose sugar fermenting yeast species, to hydrolyze xylan into xylooligosaccharides via cloning and heterologous extracellular expression of EXNI gene from locally isolated Trichoderma virens species. Pichia stipitis was engineered to carry the EXNI gene of T. virens using pGAPZα expression vector. The open reading frame encodes 191 amino acids and SDS-PAGE analysis revealed a 24 kDA recombinant protein. The EXNI activity expressed by recombinant P. stipitis clone under standard conditions using 1% beechwood xylan was 31.7 U/ml. Molecular docking and molecular dynamics simulations were performed to investigate EXNI-xylan interactions. Free EXNI and xylan bound EXNI exhibited similar stabilities and structural behavior in aqueous medium. Furthermore, this in silico work opens avenues for the development of newer generation EXN proteins that can perform better and have enhanced catalytic activity.

Heterologous Expression and Characterization of an Acidic GH11 Family Xylanase from Hypocrea orientalis

A gene encoding glycoside hydrolase family 11 xylanase (HoXyn11B) from Hypocrea orientalis EU7-22 was expressed in Pichia pastoris with a high activity (413 IU/ml). HoXyn11B was partly N-glycosylated and appeared two protein bands (19-29 kDa) on SDS-PAGE. The recombinant enzyme exhibited optimal activity at pH 4.5 and 55 °C, and retained more than 90% of the original activity after incubation at 50 °C for 60 min. The determined apparent K _m and V _max values using beechwood xylan were 10.43 mg/ml and 3246.75 IU/mg, respectively. The modes of action of recombinant HoXyn11B on xylo-oligosaccharides (XOSs) and beechwood xylan were investigated by thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), which indicated that the modes of action of HoXyn11B are different from HoXyn11A since it is able to release a significant amount of xylose from various substrates. This study provides an opportunity to better understand the hydrolysis mechanisms of xylan by xylanases from Trichoderma.

Codon Optimization of the "Bos Taurus Chymosin" Gene for the Production of Recombinant Chymosin in Pichia pastoris

Codon optimization of the Bos taurus Chymosin gene (CYM) for its expression in Pichia pastoris was performed in this study. A synthetic CYM gene was designed in silico by replacing codons rarely used by P. pastoris with equivalent nucleotide combinations that codify for the same amino acid but that are more frequently encountered in the genome of P. pastoris. A total of 332 nucleotides were modified to optimize 289 codons. The synthetic CYM gene was cloned into the expression vector pPICZαA and transformed into P. pastoris. The transformed strains were grown in artificial media supplemented with glycerol as a carbon source to increase biomass and then cultured in a similar medium replacing glycerol with methanol as a carbon source to initiate gene induction. Raw extracts of the growth media exhibited milk-clotting activity of 146.11 SU/mL. Produced recombinant chymosin showed coagulant activity from 25 to 50 °C, and within a pH range of 5-6.9, having optimum activity at 35-40 °C, and pH 5.0. These results show that codon optimization is a viable strategy to improve CYM gene expression levels in P. pastoris for the production of recombinant chymosin.

Expressing accessory proteins in cellulolytic Yarrowia lipolytica to improve the conversion yield of recalcitrant cellulose

BACKGROUND

A recently constructed cellulolytic Yarrowia lipolytica is able to grow efficiently on an industrial organosolv cellulose pulp, but shows limited ability to degrade crystalline cellulose. In this work, we have further engineered this strain, adding accessory proteins xylanase II (XYNII), lytic polysaccharide monooxygenase (LPMO), and swollenin (SWO) from Trichoderma reesei in order to enhance the degradation of recalcitrant substrate.

RESULTS

The production of EG I was enhanced using a promoter engineering strategy. This provided a new cellulolytic Y. lipolytica strain, which compared to the parent strain, exhibited higher hydrolytic activity on different cellulosic substrates. Furthermore, three accessory proteins, TrXYNII, TrLPMOA and TrSWO, were individually expressed in cellulolytic and non-cellulolytic Y. lipolytica. The amount of rhTrXYNII and rhTrLPMOA secreted by non-cellulolytic Y. lipolytica in YTD medium during batch cultivation in flasks was approximately 62 and 52 mg/L, respectively. The purified rhTrXYNII showed a specific activity of 532 U/mg-protein on beechwood xylan, while rhTrLPMOA exhibited a specific activity of 14.4 U/g-protein when using the Amplex Red/horseradish peroxidase assay. Characterization of rhTrLPMOA revealed that this protein displays broad specificity against β-(1,4)-linked glucans, but is inactive on xylan. Further studies showed that the presence of TrLPMOA synergistically enhanced enzymatic hydrolysis of cellulose by cellulases, while TrSWO1 boosted cellulose hydrolysis only when it was applied before the action of cellulases. The presence of rTrXYNII enhanced enzymatic hydrolysis of an industrial cellulose pulp and of wheat straw. Co-expressing TrXYNII and TrLPMOA in cellulolytic Y. lipolytica with enhanced EG I production procured a novel engineered Y. lipolytica strain that displayed enhanced ability to degrade both amorphous (CIMV-cellulose) and recalcitrant crystalline cellulose in complex biomass (wheat straw) by 16 and 90%, respectively.

CONCLUSIONS

This study has provided a potent cellulose-degrading Y. lipolytica strain that co-expresses a core set of cellulolytic enzymes and some accessory proteins. Results reveal that the tuning of cellulase production and the production of accessory proteins leads to optimized performance. Accordingly, the beneficial effect of accessory proteins for cellulase-mediated degradation of cellulose is underlined, especially when crystalline cellulose and complex biomass are used as substrates. Findings specifically underline the benefits and specific properties of swollenin. Although in our study swollenin clearly promoted cellulase action, its use requires process redesign to accommodate its specific mode of action.

Lignocellulose degrading extremozymes produced by Pichia pastoris: current status and future prospects

In this review article, extremophilic lignocellulosic enzymes with special interest on xylanases, β-mannanases, laccases and finally cellulases, namely, endoglucanases, exoglucanases and β-glucosidases produced by Pichia pastoris are reviewed for the first time. Recombinant lignocellulosic extremozymes are discussed from the perspectives of their potential application areas; characteristics of recombinant and native enzymes; the effects of P. pastoris expression system on recombinant extremozymes; and their expression levels and applied strategies to increase the enzyme expression yield. Further, effects of enzyme domains on activity and stability, protein engineering via molecular dynamics simulation and computational prediction, and site-directed mutagenesis and amino acid modifications done are also focused. Superior enzyme characteristics and improved stability due to the proper post-translational modifications and better protein folding performed by P. pastoris make this host favourable for extremozyme production. Especially, glycosylation contributes to the structure, function and stability of enzymes, as generally glycosylated enzymes produced by P. pastoris exhibit better thermostability than non-glycosylated enzymes. However, there has been limited study on enzyme engineering to improve catalytic efficiency and stability of lignocellulosic enzymes. Thus, in the future, studies should focus on protein engineering to improve stability and catalytic efficiency via computational modelling, mutations, domain replacements and fusion enzyme technology. Also metagenomic data need to be used more extensively to produce novel enzymes with extreme characteristics and stability.

Proper ultrasound treatment increases ethanol production from simultaneous saccharification and fermentation of sugarcane bagasse

To improve the saccharification and fermentation processes, proper ultrasound was applied which resulted in the presence of cellulase complex with improved β-glucosidase ratio leading to enhanced overall ethanol yield.

Highly Thermostable Xylanase Production from A Thermophilic Geobacillus sp. Strain WSUCF1 Utilizing Lignocellulosic Biomass

Efficient enzymatic hydrolysis of lignocellulose to fermentable sugars requires a complete repertoire of biomass deconstruction enzymes. Hemicellulases play an important role in hydrolyzing hemicellulose component of lignocellulose to xylooligosaccharides and xylose. Thermostable xylanases have been a focus of attention as industrially important enzymes due to their long shelf life at high temperatures. Geobacillus sp. strain WSUCF1 produced thermostable xylanase activity (crude xylanase cocktail) when grown on xylan or various inexpensive untreated and pretreated lignocellulosic biomasses such as prairie cord grass and corn stover. The optimum pH and temperature for the crude xylanase cocktail were 6.5 and 70°C, respectively. The WSUCF1 crude xylanase was found to be highly thermostable with half-lives of 18 and 12 days at 60 and 70°C, respectively. At 70°C, rates of xylan hydrolysis were also found to be better with the WSUCF1 secretome than those with commercial enzymes, i.e., for WSUCF1 crude xylanase, Cellic-HTec2, and AccelleraseXY, the percent xylan conversions were 68.9, 49.4, and 28.92, respectively. To the best of our knowledge, WSUCF1 crude xylanase cocktail is among the most thermostable xylanases produced by thermophilic Geobacillus spp. and other thermophilic microbes (optimum growth temperature ≤70°C). High thermostability, activity over wide range of temperatures, and better xylan hydrolysis than commercial enzymes make WSUCF1 crude xylanase suitable for thermophilic lignocellulose bioconversion processes.

Expression of the Thermobifida fusca xylanase Xyn11A in Pichia pastoris and its characterization

BACKGROUND

Xylan is a major component of plant cells and the most abundant hemicellulose. Xylanases degrade xylan into monomers by randomly cleaving β-1,4-glycosidic bonds in the xylan backbone, and have widespread potential applications in various industries. The purpose of our study was to clone and express the endoxylanase gene xynA of Thermobifida fusca YX in its native form and with a C-terminal histidine (His) tag in Pichia pastoris X-33. We analyzed and compared these two forms of the protein and examined their potential applications in various industries.

RESULTS

The xynA gene from T. fusca YX was successfully cloned and expressed using P. pastoris X-33. We produced a recombinant native form of the protein (rXyn11A) and a C-terminal His-tagged form of the desired protein (rXyn11A-(His)6). The specific activities of rXyn11A and rXyn11A-(His)6 in culture supernatants approached 149.4 and 133.4 U/mg, respectively. These activities were approximately 4- and 3.5-fold higher than those for the non-recombinant wild-type Xyn11A (29.3 U/mg). Following purification, the specific activities of rXyn11A and rXyn11A-(His)6 were 557.35 and 515.84 U/mg, respectively. The specific activity of rXyn11A was 8% higher than that of rXyn11A-(His)6. Both recombinant xylanases were optimally active at 80°C and pH 8.0, and exhibited greater than 60% activity between pH 6-9 and 60-80°C. They exhibited similar pH stability, while rXyn11A exhibited better thermostability; N-glycosylation enhanced the thermostability of both recombinant xylanases. The products of beechwood xylan hydrolyzed by both xylanases included xylobiose, xylotriose, xylotetraose and xylopentaose.

CONCLUSIONS

The C-terminal His tag had adverse effects when added to the Xyn11A protein. The thermostability of both recombinant xylanases was enhanced by N-glycosylation. Their stabilities at a high pH and temperature indicate their potential for application in various industries.

Isolation and cultivation of xylanolytic and cellulolytic Sarocladium kiliense and Trichoderma virens from the gut of the termite Reticulitermes santonensis

The purpose of this work was the isolation and cultivation of cellulolytic and xylanolytic microorganisms extracted from the gut of the lower termite Reticulitermes santonensis. Microcrystalline cellulose (with and without lignin) and beech wood xylan were used as diets instead of poplar wood in order to select cellulose and hemicellulose-degrading fungi. The strain Sarocladium kiliense (Acremonium kiliense) CTGxxyl was isolated from the termites fed on xylan, while the strain Trichoderma virens CTGxAviL was isolated from the termites fed on cellulose (with and without lignin). Both molds were cultivated in liquid media containing different substrates: agro-residues or purified polymers. S. kiliense produced maximal β-glucosidase, endo-1,4-β-D-glucanase, exo-1,4-β-D-glucanase and endo-1,4-β-D-xylanase activities of 0.103, 3.99, 0.53, and 40.8 IU/ml, respectively. T. virens produced maximal β-xylosidase, endo-1,4-β-D-glucanase, exo-1,4-β-D-glucanase, and endo-1,4-β-D-xylanase activities of 0.38, 1.48, 0.69, and 426 IU/ml. The cellulase and the xylanase of S. kiliense, less common than T. virens, were further investigated. The optimal activity of the xylanase was observed at pH 9-10 at 60 °C. The cellulase showed its maximal activity at pH 10, 70 °C. Zymography identified different xylanases produced by both molds, and some fragment sizes were highlighted: 35, 100, and 170 kDa for S. kiliense and 20, 40, 80, and 170 kDa for T. virens. In both cases, endo-1,4-β-D-xylanase activities were confirmed through mass spectrometry.

High-level expression and characterization of a thermostable xylanase mutant from Trichoderma reesei in Pichia pastoris

A gene encoding xylanase 2 mutant from Trichoderma reesei (T2C/T28C, named mxyn2) was cloned into the Pichia pastoris X33 strain using the vector pPICZαA. Recombinant Mxyn2p was functionally expressed in P. pastoris X33 and secreted into the supernatant. Real time qPCR demonstrated that an increase in gene copy number correlated with higher levels of expression. Supernatant from methanol induced cells was concentrated by ultrafiltration with a 10kDa cut off membrane, and purified with ion exchange chromatography using SP Sepharose Fast Flow chromatography. Recombinant Mxyn2p protein had the highest activity at 75°C, while recombinant protein encoded by the "wild type" xylanase gene xyn2, also expressed in Pichia, was 20°C lower. The Mxyn2p enzyme retained more than 70% of its activity after incubation at 80°C for 10min. The effects of the optimal pH and temperature for higher expression levels in P. pastoris were also determined, 6.0 and 22°C, respectively. The maximum xylanase activity of Mxyn2p was 13,000nkat/mg (9.88g/l) in fed-batch cultivation after 168h induction with methanol in a 50l bioreactor.

Identification of an endo-1,4-beta-xylanase of Ustilago maydis

Background

The utilization of raw biomass components such as cellulose or hemicellulose for the production of valuable chemicals has attracted considerable research interest in recent years. One promising approach is the application of microorganisms that naturally convert biomass constituents into value added chemicals. One of these organisms – Ustilago maydis – can grow on xylan, the second most abundant polysaccharide in nature, while at the same time it produces chemicals of biotechnological interest.

Results

In this study, we present the identification of an endo-1,4-beta xylanase responsible for xylan degradation. Xylanase activity of U. maydis cells was indirectly detected by the quantification of released reducing sugars and could be confirmed by visualizing oligosaccharides as degradation products of xylan by thin layer chromatography. A putative endo-1,4-beta-xylanase, encoded by um06350.1, was identified in the supernatant of xylan-grown cells. To confirm the activity, we displayed the putative xylanase on the surface of the xylanase negative Saccharomyces cerevisiae EBY100. The presented enzyme converted xylan to xylotriose, similar to the source organism U. maydis.

Conclusions

The xylan degradation ability together with its unicellular and yeast-like growth makes U. maydis MB215 a promising candidate for the production of valuable chemicals such as itaconic acid or glycolipids from lignocellulosic biomass. Therefore, the characterization of the endo-1,4-beta-xylanase, encoded by um06350.1, is a further step towards the biotechnological application of U. maydis and its enzymes.

Insights into exo- and endoglucanase activities of family 6 glycoside hydrolases from Podospora anserina

The ascomycete Podospora anserina is a coprophilous fungus that grows at late stages on droppings of herbivores. Its genome encodes a large diversity of carbohydrate-active enzymes. Among them, four genes encode glycoside hydrolases from family 6 (GH6), the members of which comprise putative endoglucanases and exoglucanases, some of them exerting important functions for biomass degradation in fungi. Therefore, this family was selected for functional analysis. Three of the enzymes, P. anserina Cel6A (PaCel6A), PaCel6B, and PaCel6C, were functionally expressed in the yeast Pichia pastoris. All three GH6 enzymes hydrolyzed crystalline and amorphous cellulose but were inactive on hydroxyethyl cellulose, mannan, galactomannan, xyloglucan, arabinoxylan, arabinan, xylan, and pectin. PaCel6A had a catalytic efficiency on cellotetraose comparable to that of Trichoderma reesei Cel6A (TrCel6A), but PaCel6B and PaCel6C were clearly less efficient. PaCel6A was the enzyme with the highest stability at 45°C, while PaCel6C was the least stable enzyme, losing more than 50% of its activity after incubation at temperatures above 30°C for 24 h. In contrast to TrCel6A, all three studied P. anserina GH6 cellulases were stable over a wide range of pHs and conserved high activity at pH values of up to 9. Each enzyme displayed a distinct substrate and product profile, highlighting different modes of action, with PaCel6A being the enzyme most similar to TrCel6A. PaCel6B was the only enzyme with higher specific activity on carboxymethylcellulose (CMC) than on Avicel and showed lower processivity than the others. Structural modeling predicts an open catalytic cleft, suggesting that PaCel6B is an endoglucanase.

Genetic engineering of microorganisms for biodiesel production

Biodiesel, as one type of renewable energy, is an ideal substitute for petroleum-based diesel fuel and is usually made from triacylglycerides by transesterification with alcohols. Biodiesel production based on microbial fermentation aiming to establish more efficient, less-cost and sustainable biodiesel production strategies is under current investigation by various start-up biotechnology companies and research centers. Genetic engineering plays a key role in the transformation of microbes into the desired cell factories with high efficiency of biodiesel production. Here, we present an overview of principal microorganisms used in the microbial biodiesel production and recent advances in metabolic engineering for the modification required. Overexpression or deletion of the related enzymes for de novo synthesis of biodiesel is highlighted with relevant examples.

Characterization and pH-dependent substrate specificity of alkalophilic xylanase from Bacillus alcalophilus

The gene of endo-beta-1-4 xylanase, xynT, was cloned from Bacillus alcalophilus AX2000 and expressed in Escherichia coli. This XynT, which belongs to glycoside hydrolase (GH) family 10, was found to have a molecular weight of approximately 37 kDa and exhibit optimal activity at pH 7-9 and 50 °C. It exhibits a high activity towards birchwood xylan and has the ability to bind avicel. Under optimal conditions, XynT hydrolyzes all xylooligomers into xylobiose as an end product with a preference for cleavage sites at the second or third glycosidic bond from the reducing end. XynT has a different substrate affinity on xylooligomers at pH 5.0, which contributes to its low activity toward xylotriose and its derived intermediate products. This low activity may be due to an unstable interaction with the amino acids that constitute subsites of the active site. Interestingly, the addition of Co(2+) and Mn(2+) led to a significant increase in activity by up to 40 and 50 %, respectively. XynT possesses a high binding affinity and hydrolytic activity toward the insoluble xylan, for which it exhibits high activity at pH 7-9, giving rise to its efficient biobleaching effect on Pinus densiflora kraft pulp.

Achieving efficient protein expression in Trichoderma reesei by using strong constitutive promoters

Backgrounds

The fungus Trichoderma reesei is an important workhorse for expression of homologous or heterologous genes, and the inducible cbh1 promoter is generally used. However, constitutive expression is more preferable in some cases than inducible expression that leads to production of unwanted cellulase components. In this work, constitutive promoters of T. reesei were screened and successfully used for high level homologous expression of xylanase II.

Results

The transcriptional profiles of 13 key genes that participate in glucose metabolism in T. reesei were analyzed by quantitative real-time reverse-transcription polymerase chain reaction (RT-qPCR). The results indicated that the mRNA levels of pdc (encoding pyruvate decarboxylase) and eno (encoding enolase) genes were much higher than other genes under high glucose conditions. Recombinant T. reesei strains that homologously expressed xylanase II were constructed by using the promoters of the pdc and eno genes, and they respectively produced 9266 IU/ml and 8866 IU/ml of xylanase activities in the cultivation supernatant in a medium with high glucose concentration. The productivities of xylanase II were 1.61 g/L (with the pdc promoter) and 1.52 g/L (with the eno promoter), approximately accounted for 83% and 82% of the total protein secreted by T. reesei, respectively.

Conclusions

This work demonstrates the screening of constitutive promoters by using RT-qPCR in T. reesei, and has obtained the highest expression of recombinant xylanase II to date by using these promoters.

Optimization of a synthetic mixture composed of major Trichoderma reesei enzymes for the hydrolysis of steam-exploded wheat straw

BACKGROUND

An efficient hydrolysis of lignocellulosic substrates to soluble sugars for biofuel production necessitates the interplay and synergistic interaction of multiple enzymes. An optimized enzyme mixture is crucial for reduced cost of the enzymatic hydrolysis step in a bioethanol production process and its composition will depend on the substrate and type of pretreatment used. In the present study, an experimental design was used to determine the optimal composition of a Trichoderma reesei enzyme mixture, comprising the main cellulase and hemicellulase activities, for the hydrolysis of steam-exploded wheat straw.

METHODS

Six enzymes, CBH1 (Cel7a), CBH2 (Cel6a), EG1 (Cel7b), EG2 (Cel5a), as well as the xyloglucanase Cel74a and the xylanase XYN1 (Xyl11a) were purified from a T. reesei culture under lactose/xylose-induced conditions. Sugar release was followed in milliliter-scale hydrolysis assays for 48 hours and the influence of the mixture on initial conversion rates and final yields is assessed.

RESULTS

The developed model could show that both responses were strongly correlated. Model predictions suggest that optimal hydrolysis yields can be obtained over a wide range of CBH1 to CBH2 ratios, but necessitates a high proportion of EG1 (13% to 25%) which cannot be replaced by EG2. Whereas 5% to 10% of the latter enzyme and a xylanase content above 6% are required for highest yields, these enzymes are predicted to be less important in the initial stage of hydrolysis.

CONCLUSIONS

The developed model could reliably predict hydrolysis yields of enzyme mixtures in the studied domain and highlighted the importance of the respective enzyme components in both the initial and the final hydrolysis phase of steam-exploded wheat straw.

Heterologous Expression of Endo-1,4-beta-xylanaseA from Phanerochaete chrysosporium in Pichia pastoris

The cDNA of endo-1,4-β-xylanaseA, isolated from Phaenerocheate chrysosporium was expressed in Pichia pastoris. Using either the intrinsic leader peptide of XynA or the α-factor signal peptide of Saccharomyces cerevisiae, xylanaseA is efficiently secreted into the medium at maximum concentrations of 1,946 U/L and 2,496 U/L, respectively.

Production and characterization of Acidothermus cellulolyticus endoglucanase in Pichia pastoris

The endoglucanase (E1) from Acidothermus cellulolyticus has been used extensively in cellulase research. The goal of this work was to produce high levels of this enzyme in a system that facilitates purification. A codon-optimized synthetic gene for A. cellulolyticus E1 with a C-terminal histidine tag was cloned into the genome of Pichia pastoris. Strain KM71H expressed the most enzyme, with a yield of 550mg/L culture supernatant. The temperature optimum (80°C) and pH optimum (5.1) of the purified enzyme agree with previously determined values for the enzyme produced in other systems. Michaelis-Menten kinetic parameters were determined, using a fluorescent substrate (methylumbelliferyl-β-d-cellobioside) at various temperatures. This thermostable enzyme can be used in future cellulosic biofuels-related research.

High expression of recombinant Streptomyces sp. S38 xylanase in Pichia pastoris by codon optimization and analysis of its biochemical properties

In recent years, the biotechnological use of xylanases has grown remarkably. To efficiently produce xylanase for food processing and other industry, a codon-optimized recombinant xylanase gene from Streptomyces sp. S38 was synthesized and extracellularly expressed in Pichia pastoris under the control of AOX1 promoter. SDS-PAGE and activity assay demonstrated that the molecular mass of the recombinant xylanase was estimated to be 25 kDa, the optimum pH and optimum temperature were 5.5 and 50°C, respectively. In shake flask culture, the specific activity of the xylanase activity was 5098.28 U/mg. The K ( m ) and V ( max ) values of recombinant xylanase were 11.0 mg/ml and 10000 μmol min(-1) mg(-1), respectively. In the presence of metal ions such as Ca(2+), Cu(2+), Cr(3+) and K(+), the activity of the enzyme increased. However, strong inhibition of the enzyme activity was observed in the presence of Hg(2+). This is the first report on the expression properties of a recombinant xylanase gene from the Streptomyces sp. S38 using Pichia pastoris. The attractive biochemical properties of the recombinant xylanase suggest that it may be a useful candidate for variety of commercial applications.