endo-1,4-β-Xylanase M1 (Trichoderma viride)

endo-1,4-β-Xylanase (EC 3.2.1.8) is employed across a broad range of industries including animal feed, brewing, baking, biofuels, detergents and pulp (paper). Despite its importance, a rapid, reliable, reproducible, automatable assay for this enzyme that is based on the use of a chemically defined substrate has not been described to date. Reported herein is a new enzyme coupled assay procedure, termed the XylX6 assay, that employs a novel substrate, namely 4,6-O-(3-ketobutylidene)-4-nitrophenyl-β-4⁵-O-glucosyl-xylopentaoside. The development of the substrate and associated assay is discussed here and the relationship between the activity values obtained with the XylX6 assay versus traditional reducing sugar assays and its specificity and reproducibility were thoroughly investigated.

A range of α-L-arabinofuranosyl-(1-4)-β-D-xylo-oligosaccharides (AXOS) were produced by hydrolysis of wheat flour arabinoxylan (WAX) and acid debranched arabinoxylan (ADWAX), in the presence and absence of an AXH-d3 α-L-arabinofuranosidase, by several GH10 and GH11 β-xylanases. The structures of the oligosaccharides were characterised by GC-MS and NMR and by hydrolysis by a range of α-L-arabinofuranosidases and β-xylosidase. The AXOS were purified and used to characterise the action patterns of the specific α-L-arabinofuranosidases. These enzymes, in combination with either Cellvibrio mixtus or Neocallimastix patriciarum β -xylanase, were used to produce elevated levels of specific AXOS on hydrolysis of WAX, such as 3²-α-L-Araf-(1-4)-β-D-xylobiose (A³X), 2³-α-L-Araf-(1-4)-β-D-xylotriose (A²XX), 3³-α-L-Araf-(1-4)-β-D-xylotriose (A³XX), 2²-α-L-Araf-(1-4)-β-D-xylotriose (XA²X), 3²-α-L-Araf (1-4)-β-D-xylotriose (XA³X), 2³-α-L-Araf-(1-4)-β-D-xylotetraose (XA²XX), 3³-α-L-Araf-(1-4)-β-D-xylotetraose (XA³XX), 2³ ,3³-di-α-L-Araf-(1-4)-β-D-xylotriose (A²⁺³XX), 2³,3³-di-α-L-Araf-(1-4)-β-D-xylotetraose (XA²⁺³XX), 2⁴,3⁴-di-α-L-Araf-(1-4)-β-D-xylopentaose (XA²⁺³XXX) and 3³,3⁴-di-α-L-Araf-(1-4)-β-D-xylopentaose (XA³A³XX), many of which have not previously been produced in sufficient quantities to allow their use as substrates in further enzymic studies. For A^2,3XX, yields of approximately 16% of the starting material (wheat arabinoxylan) have been achieved. Mixtures of the α-L-arabinofuranosidases, with specific action on AXOS, have been combined with β-xylosidase and β-xylanase to obtain an optimal mixture for hydrolysis of arabinoxylan to L-arabinose and D-xylose.

The most commonly used method for the measurement of the level of endo-xylanase in commercial enzyme preparations is the 3,5-dinitrosalicylic acid (DNS) reducing sugar method with birchwood xylan as substrate. It is well known that with the DNS method, much higher enzyme activity values are obtained than with the Nelson-Somogyi (NS) reducing sugar method. In this paper, we have compared the DNS and NS reducing sugar assays using a range of xylan-type substrates and accurately compared the molar response factors for xylose and a range of xylo-oligosaccharides. Purified beechwood xylan or wheat arabinoxylan is shown to be a suitable replacement for birchwood xylan which is no longer commercially available, and it is clearly demonstrated that the DNS method grossly overestimates endo-xylanase activity. Unlike the DNS assay, the NS assay gave the equivalent colour response with equimolar amounts of xylose, xylobiose, xylotriose and xylotetraose demonstrating that it accurately measures the quantity of glycosidic bonds cleaved by the endo-xylanase. The authors strongly recommend cessation of the use of the DNS assay for measurement of endo-xylanase due to the fact that the values obtained are grossly overestimated due to secondary reactions in colour development.

A simple procedure is described for the purification of gram quantities of β-D-xylanase from a commercially available Trichoderma viride culture filtrate. Chromatography of the crude extract on CM-Sepharose CL-6B gave two partially separated peaks of β-D-xylanase activity, and for convenience these have been termed xylanases I and II. Each has cellulase activity. The cellulase and xylanase activities were not separated by further purification on Ultrogel AcA 54 or Phenyl Sepharose CL-4B. Each of these xylanases was purified essentially to homogeneity (by the criterion of isoelectric focusing) and was free of protease, amylase and glycosidase activities. Physical and kinetic properties of xylanases I and II were identical, indicating that the separation of CM-Sepharose CL-6B may simply have been an artefact of chromatography. However, this pattern was reproducible, being obtained on several occasions. Each enzyme separated into two protein bands on isoelectric focusing. The major band had a pI of 8•45 and a very minor component had a pI of 7•3. Optimal activity was at pH 4•5 and 50°C and the enzymes were stable over a pH range of 3•4–7•9 and at temperatures below 55°C. Apparent K_ms were 3•33 mg ml^-1 on rye flour arabinoxylan and 1•33 mg ml^-1 on larch wood xylan. The enzymes partially hydrolysed larch wood xylan to oligosaccharides with two or three D-xylosyl residues. Rye flour arabinoxylan was hydrolysed to high molecular weight oligosaccharides which were not fractionated on Bio-Gel P-2.

Barley straw (BS) is a potential source to obtain bioethanol and value-added products such as xylooligosaccharides (XOS) and lignin for application in diverse industries. In this study, BS was submitted to steam explosion pretreatment to valorize the main components of this lignocellulose biomass. For hemicellulose fraction valorization, different combinations of endo-β-(1,4)-D-xylanase enzyme with accessory enzymes (α-L-arabinofuranosidase, feruloy -esterase and acetylxylan-esterase) have been studied to produce XOS with a low degree of polymerization. The application of accessory enzymes combined with endo-β-(1,4)-D-xylanase enzymes turned out to be the most effective strategy for the formation of XOS. The solid fraction obtained after the pretreatment was submitted to presacharification and simultaneous saccharification and fermentation process for bioethanol production. The resulting lignin-rich residue was characterized. In this integrated process, 13.0 g XOS (DP2-DP6), 12.6 g ethanol and 16.6 g lignin were obtained from 100 g of BS, achieving the goal of valorizing this agricultural residue.

In the present study, ozone assisted autohydrolysis (OAAH) was evaluated for enhanced generation of xylooligosaccharide (XOS) from wheat bran. The total XOS yield with optimum ozone dose of 3% (OAAH-3) was found to be 8.9% (w/w biomass) at 110°C in comparison to 7.96% at 170°C by autohydrolysis (AH) alone. Although, there was no significant difference in oligomeric composition (DP 2-6), significant decrease in degradation products namely furfural (2.78-fold), HMF (3.15-fold), acrylamide (nil) and acetic acid (1.06-fold), was observed with OAAH-3 as a pretreatment option. There was 1-fold higher xylan to XOS conversion and OAAH-hydrolysate had higher DPPH radical scavenging activity than AH. PCA plots indicated clear enhancement in XOS production and lower generation of inhibitors with decrease in treatment temperature. Results of the study therefore suggest OAAH can be an effective pretreatment option that can further be integrated with downstream processing for concentration and purification of XOS.

The study used mass spectrometry imaging (MSI) to map the distribution of enzymatically degraded cell wall polysaccharides in maize stems for two genotypes and at several stages of development. The context was the production of biofuels, and the overall objective was to better describe the structural determinants of recalcitrance of grasses in bioconversion. The selected genotypes showed contrasting characteristics in bioconversion assays as well as in their lignin deposition pattern. We compared the pattern of cell wall polysaccharide degradation observed by MSI following the enzymatic degradation of tissues with that of lignin deposition. Several enzymes targeting the main families of wall polysaccharides were used. In the early stages of development, cellulose and mixed-linked β-glucans appeared as the main polysaccharides degraded from the walls, while heteroxylan products were barely detected, suggesting subsequent deposition of heteroxylans in the walls. At all stages and for both genotypes, enzymatic degradation occurred preferentially in nonlignified walls for all structural families of polysaccharides studied here. However, our results showed heterogeneity in the distribution of heteroxylan products according to their chemical structure: arabinosylated products were mostly represented in the pith center, while glucuronylated products were found at the pith periphery. The conclusions of our work are in agreement with those of previous studies. The MSI approach presented here is unique and attractive for addressing the histological and biochemical aspects of biomass recalcitrance to conversion, as it allows for a simultaneous interpretation of cell wall degradation and lignification patterns at the scale of an entire stem section.

Pineapple peel waste was utilized as an unexplored source of hemicellulose (31.8 ± 1.9%) for value addition. Hemicellulose was extracted by an alkali-based method, where the peels were incubated at different alkali concentrations (5%, 10% and 15% w/v) at temperatures ranging from 35°C to a maximum of 65°C for a fixed period of 16 h. A maximum recovery of hemicellulose (95.9 ± 2.0%) was observed after incubating extractive-free pineapple peels in 15% (w/v) alkali solution for 16 h at 45°C. Higher incubation temperatures (65°C) for 16 h, resulted in a lower yield of hemicellulose (81.7 ± 3.7%) which can be attributed to the disintegration of the hemicellulose structure due to large severity factor (temperature–time combination). With low severity factor, it was noted that higher yields (96.6 ± 0.3%) were obtained 65°C, 4 h). Hydrothermal-assisted alkali extraction was also evaluated for maximizing the recovery of pineapple peel hemicellulose. The maximum relative recovery of ˜87.6% was obtained with 10% (w/v) alkali at the end of 1.5 h of hydrothermal pretreatment (121°C and 15 psi pressure). The hemicellulose extracted by hydrothermal-assisted alkali pretreatment was enzymatically hydrolyzed to produce XOS and the process was optimized in terms of enzyme dose (U), temperature (°C), pH and time (h). Direct hydrolysis of pineapple peels with dilute nitric acid produced xylose-rich liquor (˜91% xylose yield) at 0.5% nitric acid, reaction time of 1 h and solid-liquid ratio of 1:20. The xylose-rich liquor could be converted to potential chemicals such as xylitol.

Hemicelluloses are β-(1→4)-linked backbone polysaccharides found in plant cell walls that include xyloglucans, xylans, mannans and glucomannans, and play important roles in plant tissue configuration. In this study, hemicelluloses were isolated from the apical, middle and basal segments of 6 m Phyllostachys edulis culm using KOH and DMSO extraction procedures, respectively. Chemical composition and structural characterization of hemicellulosic fractions were comparatively investigated by a combination of HPLC, GPC, FT-IR, ¹H-, ¹³C-, HSQC NMR and TGA techniques. Our results show that the main chain of hemicellulose in P. edulis consists of glucuronoarabinoxylans (GAXs) with backbone 1, 4-β-d-Xyl, and side chain arabinose, glucuronic acid and acetylation. Hemicellulose content and molecular weight increased with culm xylogenesis in P. edulis. Our results provide new insights on the dynamics of hemicellulose structure in culm xylogenesis in P. edulis.

Background: α-L-Arabinofuranosidase (ARA), a debranching enzyme that can remove arabinose substituents from arabinoxylan and arabinoxylooligomers (AXOS), promotes the hydrolysis of the arabinoxylan fraction of biomass; however, the impact of ARA on the overall digestibility of cellulose is controversial. In this study, we investigated the effects of the addition of ARA on cellulase hydrolytic action. Results: We found that approximately 15% of the xylan was converted into AXOS during the hydrolysis of aqueous ammonia-pretreated corn stover and that this AXOS fraction was approximately 12% substituted with arabinose. The addition of ARA removes a portion of the arabinose decoration, but the resulting less-substituted AXOS inhibited cellulase action much more effectively; showing an increase of 45.7%. Kinetic experiments revealed that AXOS with a lower degree of arabinose substitution showed stronger affinity for the active site of cellobiohydrolase, which could be the mechanism of increased inhibition. Conclusions: Our findings strongly suggest that the ratio of ARA and other xylanases should be carefully selected to avoid the strong inhibition caused by the less-substituted AXOS during the hydrolysis of arabinoxylan-containing biomass. This study advances our understanding of the inhibitory mechanism of xylooligomers and provides critical new insights into the relationship of ARA addition and cellulose digestibility.

Background: Beer is the most popular alcoholic beverage worldwide. In the manufacture of beer, various by-products and residues are generated, and the most abundant (85% of total by-products) are spent grains. Thanks to its high (hemi)cellulose content (about 50% w/w dry weight), this secondary raw material is attractive for the production of second-generation biofuels as butanol through fermentation processes. Results: This study reports the ability of two laccase preparations from Pleurotus ostreatus to delignify and detoxify milled brewer’s spent grains (BSG). Up to 94% of phenols reduction was achieved. Moreover, thanks to the mild conditions of enzymatic pretreatment, the formation of other inhibitory compounds was avoided allowing to apply the sequential enzymatic pretreatment and hydrolysis process (no filtration and washing steps between the two phases). As expected, the high detoxification and delignification yields achieved by laccase pretreatment resulted in great saccharification. As a fact, no loss of carbohydrates was observed thanks to the novel sequential strategy, and thus the totality of polysaccharides was hydrolysed into fermentable sugars. The enzymatic hydrolysate was fermented to acetone-butanol-ethanol (ABE) by Clostridium acetobutilycum obtaining about 12.6 g/L ABE and 7.83 g/L butanol within 190 h. Conclusions: The applied sequential pretreatment and hydrolysis process resulted to be very effective for the milled BSG, allowing reduction of inhibitory compounds and lignin content with a consequent efficient saccharification. C. acetobutilycum was able to ferment the BSG hydrolysate with ABE yields similar to those obtained by using synthetic media. The proposed strategy reduces the amount of wastewater and the cost of the overall process. Based on the reported results, the potential production of butanol from the fermentation of BSG hydrolysate can be envisaged.

The effects of cellobiose and glucose as product inhibitors on the hydrolysis of lignocelluloses by cellulase has been confirmed, but the effect of these species on xylanase is still unknown. In this work, the inhibitory effects of cellulose and its derivatives on xylanase in the hydrolysis of Chinese pennisetum, a potential lignocellulosic biomass for the production of biofuels, was investigated. It was found that cellulose, cellobiose, and glucose all have negative effects on the hydrolytic action of endo-xylanase but not on that of β-xylosidase. Among these inhibitors, cellobiose exhibited the strongest inhibitory effect on xylanase, followed by glucose and cellulose. Cellulose (50 mg/mL), cellobiose (50 mg/mL), and glucose (50 mg/mL) decreased the hydrolysis yields of xylan by 10.4%, 19.7%, and 17.7%, respectively. Kinetic analysis revealed that both cellobiose and glucose competitively inhibited the activity of xylanase. The conclusions of this work help us further understand the inhibitory effects of cellulose derivatives on the hydrolysis of lignocelluloses.

The development of a bio-based economy requires the utilization of lignocellulosic biomass in a cost-effective way. The economic viability of lignocellulosic biomass-based industries is hindered by our imperfect understanding of biomass structure and suboptimal industrial processes. To achieve such goals requires direct and rapid monitoring of lignocellulosic polymers as they are physically, chemically, and/or enzymatically treated. In this study, the recently reported fluorescent protein tagged carbohydrate binding modules method (FTCM) was used to specifically track mechanical, chemical and enzymatic-induced variations of hemicelluloses at the surface of different wood fibers. Our results showed that susceptibility to hydrolysis in kraft pulp was higher for xylan, while mannan was more vulnerable in mechanical pulps. Furthermore, FTCM rapidly and efficiently detected enzymatic inactivation and the apparent complementarity (additive and/or synergistic effect) between cellulase and other enzymes (xylanase and mannanase), significantly bolstering cellulose and hemicelluloses hydrolysis. Subsequent addition of xylanase and mannanase enzymes directly proved that xylan was acting as a physical shield which was covering mannan in bleached kraft pulp. This study suggests that mannan was closely associated with cellulose or was deeply embedded in the cell wall organization of such fibers. FTCM provided direct support for previous models on fiber structure that were based on time-consuming and complicated approaches (i.e.chromatography, spectroscopy and microscopy). FTCM allowed for the monitoring of layers of polymers as they were exposed after treatments, providing key information regarding hydrolysis optimization and the specific susceptibility of xylan and mannan to biomass treatments. We believe that by applying this simple and rapid method on site, biomass industries could substantially improve cost-effectiveness of production of biofuels and other lignocellulosic biomass-based products.

Background: Thermophilic microorganisms and their enzymes offer several advantages for industrial application over their mesophilic counterparts. For example, a hyperthermophilic anaerobe, Caldicellulosiruptor bescii, was recently isolated from hot springs in Kamchatka, Siberia, and shown to have very high cellulolytic activity. Additionally, it is one of a few microorganisms being considered as viable candidates for consolidated bioprocessing applications. Moreover, C. bescii is capable of deconstructing plant biomass without enzymatic or chemical pretreatment. This ability is accomplished by the production and secretion of free, multi-modular and multi-functional enzymes, one of which, CbCel9A/Cel48A also known as CelA, is able to outperform enzymes found in commercial enzyme preparations. Furthermore, the complete C. bescii exoproteome is extremely thermostable and highly active at elevated temperatures, unlike commercial fungal cellulases. Therefore, understanding the functional diversity of enzymes in the C. bescii exoproteome and how inter-molecular synergy between them confers C. bescii with its high cellulolytic activity is an important endeavor to enable the production of more efficient biomass degrading enzyme formulations and in turn, better cellulolytic industrial microorganisms. Results: To advance the understanding of the C. bescii exoproteome we have expressed, purified, and tested four of the primary enzymes found in the exoproteome and we have found that the combination of three or four of the most highly expressed enzymes exhibit synergistic activity. We also demonstrated that discrete combinations of these enzymes mimic and even improve upon the activity of the whole C. bescii exoproteome, even though some of the enzymes lack significant activity on their own. Conclusions: We have demonstrated that it is possible to replicate the cellulolytic activity of the native C. bescii exoproteome utilizing a minimal gene set, and that these minimal gene sets are more active than the whole exoproteome. In the future, this may lead to more simplified and efficient cellulolytic enzyme preparations or yield improvements when these enzymes are expressed in microorganisms engineered for consolidated bioprocessing.

Apple pomace, potato peels, and coffee silverskin are attractive agrofood wastes for the production of biofuels and chemicals, due to their abundance and carbohydrate content. As lignocellulosic biomasses, their conversion is challenged by the presence of lignin that prevents hydrolysis of polysaccharides, hence demanding a pretreatment step. In this work, the effectiveness of Pleurotus ostreatus laccases (with and without mediator) to remove lignin, improving the subsequent saccharification, was assessed. Optimized conditions for sequential protocol were set up for all agrofood wastes reaching delignification and detoxification yields correlated with high saccharification. Especially noteworthy were results for apple pomace and coffee silverskin for which 83% of and 73% saccharification yields were observed, by using laccase and laccase mediator system, respectively. The herein developed sequential protocol, saving soluble sugars and reducing the amount of wastewater, can improve the overall process for obtaining chemicals or fuels from agrofood wastes.

Uneven distribution of AX and BG in lateral and longitudinal dimensions of a wheat grain was observed by three-dimensional MS imaging, presumably related to specific physicochemical properties of cell walls. Arabinoxylans (AX) and β-glucans (BG) are the main hemicelluloses that comprise the primary walls of starchy endosperm. These components are not evenly distributed in the endosperm, and the impact of their distribution on cell wall properties is not yet fully understood. Combined with on-tissue enzymatic degradation of the cell walls, mass spectrometry imaging (MSI) was used to monitor the molecular structure of AX and BG in thirty consecutive cross-sections of a mature wheat grain. A 3D image was built from the planar images, showing the distribution of these polymers at the full-grain level, both in lateral and longitudinal dimensions. BGs were more abundant at the vicinity of the germ and in the central cells of the endosperm, while AX, and especially highly substituted AX, were more abundant close to the brush and in the cells surrounding the crease (i.e., the transfer cells). Compared with the previously reported protocol, significant improvements were made in the tissue preparation to better preserve the shape of the fragile sections. This allowed to us achieve a good-quality 3D reconstruction from the consecutive 2D images. By providing a continuous view of the molecular distribution of the cell wall components across and along the grain, the three-dimensional images obtained by MSI may help understand the structure–function relationships of cell walls. The method should be readily extendable to other parietal polymers by selecting the appropriate enzymes.

The compositions and physical properties of pretreated lignocellulose vary depending on pretreatment methods; therefore, enzyme cocktails specific to pretreatments are desired for efficient saccharification of lignocellulose. Here, enzyme cocktails consisting of three pure lignocellulolytic enzymes endoglucanase (EG), cellobiohydrolase (CBH) and endoxylanase (XN) with a fixed amount of β-glucosidase were tailored for acid- and alkali-pretreated sugarcane bagasse (ACID and ALKALI, respectively). Based on a mixture design, the optimal mass ratios of EG, CBH, and XN were determined to be 61.25:38.73:0.02 and 53.99:34.60:11.41 for ACID and ALKALI, respectively. The optimized enzyme cocktail yielded a higher or comparable amount of reducing sugars from the hydrolysis of ACID and ALKALI when compared to that obtained using commercial cellulase mixtures. Using the commercial and easily available pure enzymes, this simple method for the in-house preparation of an enzyme cocktail specific to pretreated lignocellulose consisting of only four enzymes with a high level of hydrolysis will be helpful for achieving enzymatic saccharification in the lignocellulose-based biorefinery.

Mucilages are hydrocolloid solutions produced by plants for a variety of functions, including the creation of a water-holding barrier around seeds. Here we report our discovery of the formation of three distinct mucilage layers around Plantago ovata seeds upon their hydration. Each layer is dominated by different arabinoxylans (AXs). These AXs are unusual because they are highly branched and contain β-1,3-linked xylose in their side chains. We show that these AXs have similar monosaccharide and linkage composition, but vary in their polymer conformation. They also exhibit distinct rheological properties in aqueous solution, despite analytical techniques including NMR showing little difference between them. Using enzymatic hydrolysis and chaotropic solvents, we reveal that hydrogen bonding and side chain distribution are key factors underpinning the distinct rheological properties of these complex AXs.

Lignin is a key factor limiting saccharification of lignocellulosic feedstocks. In this comparative study, various lignin methods-including acetyl bromide lignin (ABL), acid detergent lignin (ADL), Klason lignin (KL), and modified ADL and KL determination methods—were evaluated for their potential to assess saccharification efficiency. Six diverse accessions of the bioenergy crop miscanthus were used for this analysis, which included accessions of Miscanthus sinensis, Miscanthus sacchariflorus, and hybrid species. Accessions showed large variation in lignin content. Lignin estimates were different between methods, but (highly) correlated to each other (0.54 ≤ r ≤ 0.94). The strength of negative correlations to saccharification efficiency following either alkaline or dilute acid pretreatment differed between lignin estimates. The strongest and most consistent correlations (−0.48 ≤ r ≤ −0.85) were obtained with a modified Klason lignin method. This method is suitable for high throughput analysis and was the most effective in detecting differences in lignin content (p < 0.001) between accessions.

Arabinoxylans (AX) and (1→3),(1→4)-β-glucans (BG) are the major components of wheat grain cell walls. Although incompletely described at the molecular level, it is known that the chemical and distributional heterogeneity of these compounds impacts the quality and use of wheat. In this work, an emerging technique based on MALDI mass spectrometry imaging (MSI) was employed to map variations in the quantity, localization, and structure of these polysaccharides in the endosperm during wheat maturation. MALDI MSI couples detailed structural information with the spatial localization observed at the micrometer scale. The enzymic hydrolysis of AX and BG was performed directly on the grain sections, resulting in the efficient formation of smaller oligosaccharides that are easily measurable through MS, with no relocation across the grain. The relative quantification of the generated oligosaccharides was achieved. The method was validated by confirming data previously obtained using other analytical techniques. Furthermore, in situ analysis of grain cell walls through MSI revealed previously undetectable intense acetylation of AX in young compared to mature grains, together with findings concerning the feruloylation of AX and different structural features of BG. These results provide new insights into the physiological roles of these polysaccharides in cell walls and the specificity of the hydrolytic enzymes involved.