Xylan

The coordinated action of carbohydrate-active enzymes has mainly been evaluated for the purpose of complete saccharification of plant biomass (lignocellulose) to sugars. By contrast, the coordinated action of accessory hemicellulases on xylan debranching and recovery is less well characterized. Here, the activity of two family GH115 α-glucuronidases (SdeAgu115A from Saccharophagus degradans, and AxyAgu115A from Amphibacillus xylanus) on spruce arabinoglucuronoxylan (AGX) was evaluated in combination with an α-arabinofuranosidase from families GH51 (AniAbf51A, aka E-AFASE from Aspergillus niger) and GH62 (SthAbf62A from Streptomyces thermoviolaceus). The α-arabinofuranosidases boosted (methyl)-glucuronic acid release by SdeAgu115A by approximately 50 % and 30 %, respectively. The impact of the α-arabinofuranosidases on AxyAgu115A activity was comparatively low, motivating its structural characterization. The crystal structure of AxyAgu115A revealed increased length and flexibility of the active site loop compared to SdeAgu115A. This structural difference could explain the ability of AxyAgu115A to accommodate more highly substituted arabinoglucuronoxylan, and inform enzyme selections for improved AGX recovery and use.

A chemo-enzymatic pathway was developed to transform 4-O-methylglucuronic acid (MeGlcpA) containing xylo-oligosaccharides from beechwood into clickable monomers capable of polymerizing at room temperature and in aqueous conditions to form unique polytriazoles. While the gluco-oligosaccharide oxidase (GOOX) from Sarocladium strictum was used to oxidize C6-propargylated oligosaccharides, the acid–amine coupling reagents 1-ethyl-3-(3-(dimethylamino)propyl) carbodiimide (EDAC) and 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) were employed and compared for their ability to append click functionalities to carboxylic acid groups of enzyme-treated oligosaccharides. While DMT-MM was a superior coupling reagent for this application, a triazine side product was observed during C-1 amidation. Resulting bifunctional xylo-oligosaccharide monomers were polymerized using a Cu(I) catalyst, forming a soft gel which was characterized by 1H NMR, confirming the triazole product.

A wood fibre is a complex multi component biocomposite that is hierarchically organised. The arrangement of a wood fibre on the ultrastructural level is highly controlled by the interactions between the main structural polymers, i.e. cellulose, various hemicelluloses and lignin, as well as in some parts also pectin and protein. This further determines the mechanical and physical properties of the wood material, and consequently its targeted applications. Despite considerable research in this field during a number of years, the current knowledge on the interactions between the wood polymers is still incomplete and needs improvement. Also, mimicking of natural structures is an inspiration when preparing new materials from renewable resources, hence a comprehensive understanding of the polymer interactions is required. The first part of this study was to improve the understanding on the molecular interactions within the primary cell wall of spruce wood fibres, and its importance for th...

Background
Dicarboxylic acids offer several applications in detergent builder and biopolymer fields. One of these acids, 4-O-methyl D-glucaric acid, could potentially be produced from glucuronoxylans, which are a comparatively underused fraction of wood and agricultural biorefineries.

Results
Accordingly, an enzymatic pathway was developed that combines AxyAgu115A, a GH115 α-glucuronidase from Amphibacillus xylanus, and GOOX, an AA7 gluco-oligosaccharide oxidase from Sarocladium strictum, to produce this bio-based chemical from glucuronoxylan. AxyAgu115A was able to release almost all 4-O-methyl D-glucuronic acid from glucuronoxylan while a GOOX variant, GOOX-Y300A, could convert 4-O-methyl D-glucuronic acid to the corresponding glucaric acid at a yield of 62%. Both enzymes worked effectively at alkaline conditions that increase xylan solubility. Given the sensitivity of AxyAgu115A to hydrogen peroxide and optimal performance of GOOX-Y300A at substrate concentrations above 20 mM, the two-step enzyme pathway was demonstrated as a sequential, one-pot reaction. Additionally, the resulting xylan was easily recovered from the one-pot reaction, and it was enzymatically hydrolysable.

Conclusions
The pathway in this study requires only two enzymes while avoiding a supplementation of costly cofactors. This cell-free approach provides a new strategy to make use of the underutilized hemicellulose stream from wood and agricultural biorefineries.

In this paper, we describe an experimental study on the hot alkali extraction of hemicelluloses from wheat straw and corn stalks, two of the most common lignocellulosic biomass constituents in Romania. The chemical compositions of the raw materials were determined analytically, and the relevant chemical components were cellulose, hemicelluloses, lignin, and ash. Using the response surface methodology, the optimum values of the hot alkaline extraction parameters, i.e., time, temperature, and NaOH concentration, were identified and experimentally validated. The physicochemical characterization of the isolated hemicelluloses was performed using HPLC, FTIR, TG, DTG, and 1H-NMR spectroscopy. The main hemicellulose components identified experimentally were xylan, arabinan, and glucan. The study emphasizes that both corn stalks and wheat straw are suitable as raw materials for hemicellulose extraction, highlighting the advantages of alkaline pretreatments and showing that optimization meth...

The development of fast-growing hardwood trees as a source of lignocellulosic biomass for biofuel and biomaterial production requires a thorough understanding of the plant cell wall structure and function that underlie the inherent recalcitrance properties of woody biomass. Downregulation of GAUT12.1 in Populus deltoides was recently reported to result in improved biomass saccharification, plant growth, and biomass yield. To further understand GAUT12.1 function in biomass recalcitrance and plant growth, here we report the effects of P. trichocarpa GAUT12.1 overexpression in P. deltoides. Increasing GAUT12.1 transcript expression by 7-49% in P. deltoides PtGAUT12.1-overexpression (OE) lines resulted in a nearly complete opposite biomass saccharification and plant growth phenotype to that observed previously in PdGAUT12.1-knockdown (KD) lines. This included significantly reduced glucose, xylose, and total sugar release (12-13%), plant height (6-54%), stem diameter (8-40%), and overall...

Plant-derived natural products are being used in medicine, and they are easily available for the production and use in tissue engineering based biological applications. Utilization of plant materials to treat human diseases is a common practice followed over many decades. In fact plant and its derivatives have been actively included in health management over thousands of years. The advent of phytochemical and phytopharmacological sciences has opened an arena to elucidate the structural and biological composition of several medicinal plant products. Their pharmacological effects depend on the supply of highly active water soluble compounds; however, due to their large molecular size most compounds are unable to cross the lipid membranes of the cells and therefore result in poor absorption resulting in loss of bioavailability and efficacy. Electrospinning makes it possible to combine the advantages of utilizing these plant materials in the form of nanofibrous scaffolds for delivering ...

Despite an increased knowledge of microbial xylanolytic systems in the past few years, further studies are required to achieve a complete understanding of the mechanism of xylan degradation by microorganisms and their enzymes. The enzyme system used by ...

Chestnut shell (CS) is an agronomic residue mainly used for extraction of antioxidants or as adsorbent of metal ions. It also contains some polysaccharide that has not been considered as potential source of fermentable sugars for biofuel production until now. In this study, the effect of different pretreatment methods on CS was evaluated in order to obtain the greatest conversion of cellulose and xylan into fermentable sugars. Hot acid impregnation, steam explosion (acid-catalysed or not), and aqueous ammonia soaking (AAS) were selected as pretreatments. The pretreated biomass was subjected to saccharification with two enzyme cocktails prepared from commercial preparations, and evaluation of the best pretreatment and enzyme cocktail was based on the yield of fermentable sugars produced. As AAS provided the best result after preliminary experiments, enhancement of sugar production was attempted by changing the concentrations of ammonium hydroxide, enzymes, and CS. The optimal pretreatment condition was 10 % ammonium hydroxide, 70 °C, 22 h with CS at 5 % solid loading. After saccharification of the pretreated CS for 72 h at 50 °C and pH 5.0 with a cocktail containing cellulase (Accellerase 1500), beta-glucosidase (Accellerase BG), and xylanase (Accellerase XY), glucose and xylose yields were 67.8 and 92.7 %, respectively.

The effects of hemicellulose and lignin on recycled pulp quality were studied using hemlock pulps. The amount of pentosans in the pulps played a critical role in their recycling potential, with pulp recyclability improving with higher pentosan content. This effect was observed in both low-yield chemical pulps and ultrahigh-yield chemimechanical pulps. For five pulp properties (apparent density, tensile strength, burst strength, tear resistance, and light-scattering coefficient), the magnitude of changes induced by recycling can be statistically explained by the variation of pentosan content alone. Lignin content did not significantly affect the recycling potential of these pulps. A mechanism is proposed to explain how xylan molecules could influence pulp recyclability. Application : demonstrates that pulp hemicellulose content - principally pentosans and especially xylan - governs the strength and optical properties of recycled pulps.

Department of Food Science, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden ... (Received 17 May 1991; revised version received 2 September 1991; accepted 9 October 1991) ... Abstract: Rye grains from Finland, Canada, Sweden and Poland were ...

From previous biomass decomposition studies, it is well established that thermolysis generally occurs between 200 and 400°C. For most materials, this temperature range constitutes up to 95% of total degradation; nonetheless, secondary decomposition reactions continue to occur in the solid matrix above 400°C. The extent of these reactions, as indicated by the material loss above 400°C, is small, and in the past has been either ignored or included in the primary degradative step. However, this latter step (reactions above 400°C) exhibits many unique characteristics that differentiate it from the primary pyrolysis step and therefore needs to be treated separately. Additionally, it is widely accepted that primary decomposition of biomass material (<400°C) consists of a degradative process, whereas the secondary thermolysis (>400°C) involves an aromatization process. In this study, It is shown that the latter step can be deconvoluted from the primary decomposition step, particularl...

Pressure cooking of corn fiber in liquid water at 160 °C and a pH maintained at 4−7 produces an aqueous stream of dissolved glucans, xylans, proteins, phenolics, and minerals. We report hydrolysis of these oligosaccharides to glucose and xylose in a fixed-bed reactor packed ...

ABSTRACT In this work, an integrated one-step alkaline extrusion process was tested as pretreatment for sugar production from barley straw (BS) biomass. The influence of extrusion temperature (T) and the ratio NaOH/BS dry matter (w/w) (R) into the extruder on pretreatment effectiveness was investigated in a twin-screw extruder at bench scale. A 2(3) factorial design of experiments was used to analyze the effect of process conditions [T: 50-100 degrees C; R: 2.5-7.5% (w/w)] on composition and enzymatic digestibility of pretreated substrate (extrudate). The optimum conditions for a maximum glucan to glucose conversion were determined to be R = 6% and T = 68 degrees C. At these conditions, glucan yield reached close to 90% of theoretical, while xylan conversion was 71% of theoretical. These values are 5 and 9 times higher than that of the untreated material, which supports the great potential of this one-step combined pre-treatment technology for sugar production from lignocellulosic substrates. The absence of sugar degradation products is a relevant advantage over other traditional methods for a biomass to ethanol production process since inhibitory effect of such product on sugar fermentation would be prevented. (C) 2013 Published by Elsevier Ltd.

Molecular engineering of ligand-binding proteins is commonly used for identification of variants that display novel specificities. Using this approach to introduce novel specificities into CBMs (carbohydrate-binding modules) has not been extensively explored. Here, we report the engineering of a CBM, CBM4-2 from the Rhodothermus marinus xylanase Xyn10A, and the identification of the X-2 variant. As compared with the wild-type protein, this engineered module displays higher specificity for the polysaccharide xylan, and a lower preference for binding xylo-oligomers rather than binding the natural decorated polysaccharide. The mode of binding of X-2 differs from other xylan-specific CBMs in that it only has one aromatic residue in the binding site that can make hydrophobic interactions with the sugar rings of the ligand. The evolution of CBM4-2 has thus generated a xylan-binding module with different binding properties to those displayed by CBMs available in Nature.