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At least 145 records · Page 8Linked to original sources
PubMed2000

A proteomic analysis of secreted proteins from xylan-induced Bacillus sp. strain K-1.

The expression level of extracellular proteins in an alkaliphilic bacterium, Bacillus sp. strain K-1, grown in a xylan-containing medium, is significantly increased when compared with that grown in the nonxylan culture medium. A proteomic approach has been efficiently applied to separate and characterize these differentially expressed secretory proteins. Eight prominent protein spots were identified and subjected to N-terminal amino acid sequencing. The results show that three spots share considerable similarity with the xylanolytic enzymes and that two spots share considerable similarity with the GltC regulatory protein and 3-dehydroquinate dehydratase, respectively. In addition, the three other proteins show little similarity with the known proteins in the database. In conclusion, our results demonstrate that the proteomic approach is a highly efficient method to rapidly study the differential expression of the secreted proteins by Bacillus sp. strain K-1 grown under xylan-induced condition.

Bacillus↗
PubMed2005

Matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectrometry of beta-(1 --> 3), beta-(1 --> 4)-xylans from Nothogenia fastigiata using nor-harmane as matrix.

Three xylan fractions isolated from the red seaweed Nothogenia fastigiata (Nemaliales) were analyzed by ultraviolet matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOFMS). UV-MALDI-TOFMS was carried out in the linear and reflectron modes, and as routine in the positive and negative ion modes. Of the several matrices tested, nor-harmane was the only effective one giving good spectra in the positive ion mode. The number-average molar masses of two of the fractions, calculated from the distribution profiles, were lower than those determined previously by (1)H NMR analysis, suggesting a decrease in the ionization efficiency with increasing molecular weight; weight-average molar mass and polydispersity index were also determined. As the xylans retained small but significant quantities of calcium salts, the influence of added Ca(2+) as CaCl(2) on UV-MALDI-MS was investigated. The simultaneous addition of sodium chloride and calcium chloride was also analyzed. Addition of sodium chloride did not change the distribution profile of the native sample showing that the inhibitory effect is due to Ca(2+) and not to Cl(-). Addition of calcium chloride with 1:1 analyte/salt molar ratio gave spectra with less efficient desorption/ionization of oligomers; the signals of these oligomers were completely suppressed when the addition of the salt became massive (1:100 analyte/salt molar ratio).

Carbolines↗
PubMed2000

Crystal structure of Streptomyces olivaceoviridis E-86 beta-xylanase containing xylan-binding domain.

Xylanases hydrolyse the beta-1,4-glycosidic bonds within the xylan backbone and belong to either family 10 or 11 of the glycoside hydrolases, on the basis of the amino acid sequence similarities of their catalytic domains. Generally, xylanases have a core catalytic domain, an N and/or C-terminal substrate-binding domain and a linker region. Until now, X-ray structural analyses of family 10 xylanases have been reported only for their catalytic domains and do not contain substrate-binding domains. We have determined the crystal structure of a family 10 xylanase containing the xylan-binding domain (XBD) from Streptomyces olivaceoviridis E-86 at 1.9 A resolution. The catalytic domain comprises a (beta/alpha)(8)-barrel topologically identical to other family 10 xylanases. XBD has three similar subdomains, as suggested from a triple-repeat sequence, which are assembled against one another around a pseudo-3-fold axis, forming a galactose-binding lectin fold similar to ricin B-chain. The Gly/Pro-rich linker region connecting the catalytic domain and XBD is not visible in the electron density map, probably because of its flexibility. The interface of the two domains in the crystal is hydrophilic, where five direct hydrogen bonds and water-mediated hydrogen bonds exist. The sugar-binding residues seen in ricin/lactose complex are spatially conserved among the three subdomains in XBD, suggesting that all of the subdomains in XBD have the capacity to bind sugars. The flexible linker region enables the two domains to move independently and may provide a triple chance of substrate capturing and catalysis. The structure reported here represents an example where the metabolic enzyme uses a ricin-type lectin motif for capturing the insoluble substrate and promoting catalysis.

Amino Acid Motifs↗
PubMed1989

Isolation and characterization of xylose- and xylan-utilizing anaerobic bacteria.

By enrichment with xylose, nine mesophilic strains of anaerobic bacteria were obtained from various sources. Two isolates appear to belong to the genus Eubacterium. Six other strains belong to the genus Clostridium. Three of the isolated strains utilized larch wood xylan. The percentage of utilization of xylose and xylan and the yield of fermentation end products--viz. acetic acid and butyric acid--are equivalent to that of Clostridium acetobutylicum (ATCC 824) and reported thermophilic strains.

Animals↗
PubMed1998

Oat beta-glucan and xylan hydrolysates as selective substrates for Bifidobacterium and Lactobacillus strains.

Novel oligomers that resist digestion in the upper gut were prepared from oat mixed-linked beta-glucan and xylan by enzymatic hydrolysis with lichenase of Bacillus subtilis and xylanase of Trichoderma reesei respectively. The low-molecular-mass hydrolysis products of beta-glucan and xylan were compared with fructooligomers and raffinose in their ability to provide growth substrates for probiotic (Lactobacillus and Bifidobacterium) and intestinal (Bacteroides, Clostridium and Escherichia coli) strains in vitro. A degradation profile of each carbohydrate and total sugar consumption were analysed with HPLC, and bacterial growth rate with an automatic turbidometer, the Bioscreen C system. beta-Glucooligomers and xylooligomers both enhanced the growth of health-promoting probiotic strains as compared with intestinal bacterial growth, but not to a significant level. Raffinose stimulated the probiotic strains significantly, whereas fructooligomers induced high average growth for intestinal bacteria also.

Bifidobacterium↗
PubMed1990

Structural features of a water-soluble L-arabino-D-xylan from rye bran.

A water-soluble L-arabino-D-xylan, obtained from the chlorite holocellulose of de-lipidated, de-starched, and de-pectinated rye bran by ammoniacal extraction, was composed of L-Ara and D-Xyl in the molar ratio 7.8:10 and had Mw 36,500 and Mn 26,950. The backbone of the polysaccharide was shown to comprise (1----4)-linked beta-D-Xylp residues, with approximately 41% unsubstituted, approximately 33% 2- or 3-substituted, and approximately 26% disubstituted. Single alpha-L-Araf groups were attached to the xylan core; only a small proportion was 2-, 3-, or 5-linked.

Carbohydrate Sequence↗
PubMed2005

Heterologous expression, purification, crystallization, X-ray analysis and phasing of the acetyl xylan esterase from Bacillus pumilus.

Bacillus pumilus PS213 acetyl xylan esterase (AXE) acts as an accessory enzyme in the plant cell wall hemicellulose biodegradation pathway. It belongs to the carbohydrate esterase family 7 and hydrolyses the ester linkages of the acetyl groups in position 2 and/or 3 of the xylose moieties of the acetylated xylan fragments from hardwood. The enzyme displays activity towards a broad range of acetylated compounds including the antibiotic cephalosporin-C. In this study we report the heterologous expression, purification, physicochemical characterization and crystallization of the recombinant B. pumilus AXE. Remarkable improvement of the crystal quality was achieved by setting up crystallization conditions, at first established using the hanging drop vapor diffusion method, in a micro-batch experiment. Rod-like diffraction quality crystals were obtained using 10% PEG 6000, 0.1 M MES pH 6.0 and a wide range of LiCl concentrations (0.2-1.0 M) as precipitant agent. Two different crystal forms, both belonging to space group P2(1), were characterized, diffracting X-rays to 2.5 and 1.9 angstrom resolution. Successful molecular replacement showed 12 molecules in the asymmetric unit of either crystal forms that are arranged as two doughnut-like hexamers, each one encompassing a local 32 symmetry. A catalytic inactive mutant Ser181Ala of B. pumilus AXE was also engineered, expressed, purified and crystallized for functional and structural studies.

Acetylesterase↗
PubMed2004

Hydrolysis of Nothogenia erinacea xylan by xylanases from families 10 and 11.

The structures of several enzymatic hydrolysis products of Nothogenia erinacea seaweed xylan, a linear homopolymer with mixed beta-(1-->3)/beta-(1-->4) linkages, were analysed by physicochemical and biochemical techniques. With the glycoside hydrolase family 10 beta-(1-->4)-xylanase from Cryptococcus adeliae, hydrolysis proceeds to a final mixture of products containing a mixed linkage-type triose as a major compound, whereas with the family 11 xylanase from Thermomyces lanuginosus this is a mixed linkage tetraose. The Cryptococcus xylanase is shown to be capable of also catalysing the hydrolysis of beta-(1-->3) linkages, that is this of a mixed type tetraose intermediary formed, in accordance with the broader substrate specificity of family 10 enzymes. From a partial degradation experiment with the T. lanuginosus xylanase, a series of higher mixed oligosaccharides were isolated and identified. The observed oligosaccharide intermediates and splicing pattern indicate an irregular beta-(1-->3)/beta-(1-->4) linkage distribution within the linear d-xylose polymer. Similar results were obtained with rhodymenan, the seaweed xylan from Palmares palmata.

Ascomycota↗
PubMed2006

Expression of recombinant Aspergillus niger xylanase A in Pichia pastoris and its action on xylan.

The mature peptide of Aspergillus niger xylanase A (AnxA) was successfully expressed in Pichia pastoris at high levels under the control of AOX1 promoter. The recombinant AnxA (reAnxA) was secreted into culture medium. After 96-h 0.25% methanol induction, the activity of reAnxA in the culture supernatant reached the peak, 175 U/mg, which was 1.9 times as high as that of the native AnxA (92 U/mg). Studies on enzymatic properties showed that the optimum temperature and optimum pH of reAnxA were 50 degrees C and 5.0, respectively. The reAnxA was very stable in a wide pH range of 3.0-8.0. After incubation at the pH 3.0-8.0, 25 degrees C for 1h, all the residual activities of reAnxA were over 80%. The K(m) and k(cat) values for reAnxA were 4.8 mg/ml and 123.2s(-1), respectively. HPLC analysis showed that xylotriose was the main hydrolysis product of birchwood xylan and bran insoluble xylan by reAnxA.

Aspergillus niger↗
PubMed1991

A novel L-fuco-4-O-methyl-D-glucurono-D-xylan from Hyptis suaveolens.

The acidic polysaccharide from the seed-coat mucilage of Hyptis suaveolens is a highly branched L-fuco-4-O-methyl-D-glucurono-D-xylan for which a structure is proposed having a 4-linked beta-D-xylan backbone carrying side chains of single 4-O-methyl-alpha-D-glucuronic acid residues at O-2 and 2-O-L-fucopyranosyl-D-xylopyranose units at O-3. The structural analysis involves base-catalyzed beta-elimination of uronic acid residues from the methylated glycan followed by degradation using a modified Svensson oxidation-elimination sequence.

Carbohydrate Sequence↗
PubMed1998

(4-O-Methyl-alpha-D-glucurono)-D-xylan from Rudbeckia fulgida, var. sullivantii (Boynton et Beadle).

From the medicinal plant Rudbeckia fulgida, var. sillivantii (Boynton et Beadle) a low-molecular-mass (4-O-methyl-alpha-D-glucurono)-D-xylan was isolated by alkaline extraction, followed by ethanol precipitation, ion-exchange chromatography and gel filtration. The results of compositional and linkage analyses, supported by those of 1H and 13C NMR measurements of oligomers generated on partial acid hydrolysis, showed the (1-->4)-linked beta-D-xylopyranosyl backbone with about 18% of 4-O-methyl-D-glucuronic acid attached to O-2 of the xylose residues. From the mean distance of adjacent carboxyl groups, obtained from experimentally determined single-ion activity coefficients of calcium counterions, it followed that the uronic acid units are separated and distributed regularly along the xylan chain, i.e. approximately each sixth D-xylose unit bears a 4-O-methyl-D-glucuronic acid residue.

Carbohydrate Sequence↗
PubMed2002

Immunomodulatory activity of acidic xylans in relation to their structural and molecular properties.

The structure/function relationship of two acidic heteroxylan types, the arabino-(glucurono)xylan from corn cobs (AGX) and 4-O-methylglucuronoxylans (GXs) from beechwood and three medicinal herbs (Rudbeckia, Altheae, and Mahonia), has been studied. The effect of the molecular mass of AGX, as well as the content and distribution of the 4-O-methylglucuronic acid side chains in GXs on the immunological activity of these xylans was characterized by their biological response in the mitogenic and comitogenic thymocyte in vitro tests. Depolymerization of AGX by ultrasonication resulted in unequivocal decrease of the immunomodulatory activity, whereas already a short treatment by endo-beta-1,4-xylanase brought about a significant increase in its activity when applied in the highest dose. In the case of the GX samples, neither the uronic acid content nor the distribution pattern of the uronic acid side chains was found to be determinant for the expression of their immunomodulatory activity.

Adjuvants, Immunologic↗
PubMed2000

Effects of purified endo-beta-1,4-xylanases of family 10 and 11 and acetyl xylan esterases on eucalypt sulfite dissolving pulp.

Sulfite dissolving pulp from Eucalyptus grandis contained approximately 3.8% O-acetyl-4-O-methylglucuronoxylan with a molar ratio of xylose:4-O-methylglucuronic acid:acetyl group close to 13.6:1:6.2. The effects produced by purified endo-xylanases from two different glycosyl hydrolase families (family 10 and 11) as well as acetyl xylan esterases were examined and assessed on pulp in relation to their bleaching abilities. The purified endo-xylanases hydrolyzed only a limited portion (less than 30%) of the acetylglucuronoxylan present in the pulp. The enzymes of family 10 produced acetylated xylobiose and xylotriose whereas acetylated xylobiose was not observed among the products released from the pulp by the family 11 xylanases. The esterases however were not capable of deacetylating the acetylated aldouronic acids generated by the xylanases. Regardless of the different mode of action of the endo-xylanases on dissolving pulp, their effect on pulp bleaching was not related to the amount and nature of sugars generated or the glycosyl hydrolase family. No additional brightness gain was obtained when endo-xylanases were used in conjunction with acetyl xylan esterases, suggesting that the latter do not play an important role in biobleaching of eucalypt sulfite dissolving pulps.

Acetylesterase↗
PubMedDate not supplied

Butanol production from corn fiber xylan using Clostridium acetobutylicum.

Acetone, butanol, and ethanol (ABE) were produced from corn fiber arabinoxylan (CFAX) and CFAX sugars (glucose, xylose, galactose, and arabinose) using Clostridium acetobutylicum P260. In mixed sugar (glucose, xylose, galactose, and arabinose) fermentation, the culture preferred glucose and arabinose over galactose and xylose. Under the experimental conditions, CFAX (60 g/L) was not fermented until either 5 g/L xylose or glucose plus xylanase enzyme were added to support initial growth and fermentation. In this system, C. acetobutylicum produced 9.60 g/L ABE from CFAX and xylose. This experiment resulted in a yield and productivity of 0.41 and 0.20 g/L x h, respectively. In the integrated hydrolysis, fermentation, and recovery process, 60 g/L CFAX and 5 g/L xylose produced 24.67 g/L ABE and resulted in a higher yield (0.44) and a higher productivity (0.47 g/L x h). CFAX was hydrolyzed by xylan-hydrolyzing enzymes, and ABE were recovered by gas stripping. This investigation demonstrated that integration of hydrolysis of CFAX, fermentation to ABE, and recovery of ABE in a single system is an economically attractive process. It is suggested that the culture be further developed to hydrolyze CFAX and utilize all xylan sugars simultaneously. This would further increase productivity of the reactor.

Butanols↗
PubMed2005

Xylans from the medicinal herb Phyllanthus niruri.

Phyllanthus niruri is a well-known medicinal herb that is widely used in Asia, Africa, and South America. The characterization of two purified polysaccharides from the whole plant has been investigated. Methylation analysis and (13)C NMR spectroscopy showed the chemical structure of two xylans. A hot 15% aqueous KOH fraction yielded a linear beta-(1-->4)-linked xylan, and 2% aqueous KOH afforded a complex acidic heteroxylan, with a (1-->4)-linked beta-Xylp main chain, substituted by rhamnose, arabinose, and 4-O-methylglucuronic acid side chains. These contained nonreducing end-units of arabinose, xylose, galactose, glucose, and nonmethylated glucuronic acid.

Brazil↗
PubMed2002

Influence of aromatic compounds on biodegradation of [14C]-labeled xylan and mannan by the white-rot fungus Phlebia radiata.

Radiolabeled [14C]arabinoxylan from wheat meal and [14C]galactoglucomannan from red clover meal were prepared by using 14CO2 as a precursor. Twice as much mannan was mineralized than xylan after 14 days of incubation with Phlebia radiata. Low-molecular-weight phenolic compounds structurally related to lignin increased during mineralization of both hemicellulose fractions. Veratryl alcohol increased degradation of arabinoxylan by approximately 28.5%, whereas veratric acid increased it by only 9.0%. Vanillic acid and ferulic acid also stimulated degradation by 16.6% and 34.7%, respectively. Veratryl alcohol and ferulic acid increased degradation of galactoglucomannan by approximately 75%. Veratraldehyde in both cases repressed the degradation process (23.6% arabinoxylan, 43.8% galactoglucomannan). These results indicate that the degradation of hemicelluloses, e.g., xylan and mannan, by P. radiata is enhanced by addition of aromatic compounds.

Benzaldehydes↗
PubMed1998

Substrate-binding domains of glycanases from Streptomyces lividans: characterization of a new family of xylan-binding domains.

The substrate-binding domains of six glycanases from Streptomyces lividans were investigated to determine their specificity towards cellulose and xylan. Based upon amino acid sequence similarities, four of the six domains could be assigned to existing cellulose-binding domain families. However, the binding domains of xylanase A and arabinofuranosidase B could not be classified in any of the known families and should therefore be classified as members of a new family. Evidence is also presented that this new family is one of true xylan-binding domains.

Amino Acid Sequence↗
PubMed2000

The Aspergillus niger transcriptional activator XlnR, which is involved in the degradation of the polysaccharides xylan and cellulose, also regulates D-xylose reductase gene expression.

Screening of an Aspergillus niger differential cDNA library, constructed by subtracting cDNA fragments of a xlnR loss-of-function mutant from wild-type cDNA fragments, resulted in the cloning of the gene encoding D-xylose reductase (xyrA). Northern blot analysis using an A. niger wild-type strain, a xlnR multiple-copy strain and a xlnR loss-of-function mutant confirmed that the xyrA gene is regulated by XlnR, the transcriptional activator of the xylanolytic enzyme system in A. niger. D-xylose reductase catalyses the NADPH-dependent reduction of D-xylose to xylitol, which is the first step in D-xylose catabolism in fungi. Until now, XlnR was shown to control the transcription of genes encoding extracellular hydrolytic enzymes involved in cellulose and xylan degradation. In the present study, we show that A. niger is able to harmonize its sugar metabolism and extracellular xylan degradation via XlnR by regulating the expression of XyrA.

Aldehyde Reductase↗