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Query: UNIPROT:P06889 (Mol)
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Two genes from Thermoanaerobacterium thermosulfurigenes EM1 were identified which are predicted to encode a xylanase (XynA) and a polygalacturonate hydrolase (Pg1A). The xynA gene has the potential to encode a 1234-amino acid product consisting of a signal peptide followed by a repeated domain, a xylanase family F domain, two cellulose-binding domains and a triplicated sequence at its C-terminus. The gene pglA is predicted to encode a product of 1148 amino acids consisting of a signal sequence followed by a fibronectin type III-like domain (Fn3 domain), the catalytic domain, a Gly/Thr/Ser/Asn-rich segment and a triplicated domain. The triplicated segments at the C-termini of deduced XynA and Pg1A are about 95% identical to each other and to the S-layer-like domains of the previously characterized pullulanase (AmyB) from the same organism. In contrast, sequence comparisons revealed only distant amino acid sequence similarities between the fibronectin type III-like domains of Pg1A and AmyB from T. thermosulfurigenes EM1.
Mol Gen Genet 1996 Sep 25
PMID:Characterization of genes from Thermoanaerobacterium thermosulfurigenes EM1 that encode two glycosyl hydrolases with conserved S-layer-like domains. 887 52

The crystal structure of endo-1,4-beta-xylanase I from Aspergillus niger has been solved by molecular replacement and was refined to 2.4 A resolution. The final R-factor for all data from 6 to 2.4 A is 17.9%. The A. niger xylanase has a characteristic fold which is unique for family G xylanases (root-mean-square deviation = 1.1 A to Trichoderma reesei xylanase I, which has 53% sequence identity). It consists of a single domain composed predominantly of beta-strands. Two beta-sheets are twisted around a deep, long cleft, which is lined with many aromatic amino acid residues and is large enough to accommodate at least four xylose residues. The two conserved glutamate residues, Glu79 and Glu170, which are likely to be involved in catalysis, reach into this cleft from opposite sides. A niger xylanase I is of particular commercial interest because of its low pH optimum. A model is proposed which explains this low pH optimum compared to other members of xylanase family G.
J Mol Biol 1996 Oct 18
PMID:Three-dimensional structure of Endo-1,4-beta-xylanase I from Aspergillus niger: molecular basis for its low pH optimum. 889 Sep 13

The filamentous fungus Trichoderma reesei forms two specific, xylan-inducible xylanases encoded by xyn1 and xyn2 to degrade the beta-1,4-D-xylan backbone of hemicelluloses. This enzyme system is formed in the presence of xylan, but not glucose. The molecular basis of the absence of xylanase I formation on glucose was the purpose of this study. Northern blotting of the xyn1 transcript as well as the use of the Escherichia coli hygromycin B phosphotransferase-encoding gene (hph) as a reporter consistently showed that the basal expression of xyn1 was affected by glucose, whereas its induction by xylan remained uninfluenced. The repression of basal xyn1 transcription is mediated by the carbon catabolite repressor protein Cre1, which in vivo binds to two of four consensus sites (5'-SYG-GRG-3') in the xyn1 promoter, which occurred in the form of an inverted repeat. T. reesei strains, bearing a xyn1::hph reporter construct, in which four nucleotides from the middle of the inverted repeat had been removed, expressed hph on glucose at a level comparable to that observed during growth on a carbon catabolite derepressing carbon source. Northern analysis of xyn1 expression in a T. reesei mutant strain (RUT C-30), which contains a truncated, non-functional cre1 gene, also confirmed basal transcription of xyn1. In this strain, xyn1 transcription was still inducible by xylose or xylan to an even higher degree than in the wild-type strain, suggesting that induction overcomes glucose repression at the level of xyn1 expression. Based on these data, we postulate that basal transcription of xyn1 is repressed by glucose and mediated by an inverted repeat of the consensus motif for Cre1-mediated carbon catabolite repression.
Mol Microbiol 1996 Sep
PMID:Carbon catabolite repression of xylanase I (xyn1) gene expression in Trichoderma reesei. 889 95

In culture, the filamentous fungus Cochliobolus carbonum, a pathogen of maize, makes three cationic xylanases, XYL1, which encodes the major endoxylanase (Xyl1), was earlier cloned and shown by gene disruption to encode the first and second peaks of xylanase activity (P. C. Apel, D. G. Panaccione, F. R. Holden, and J. D. Walton, Mol. Plant-Microbe Interact. 6:467-473, 1993). Two additional xylanase genes, XYL2 and XYL3, have now been cloned from C. carbonum. XYL2 and XYL3 are predicted to encode 22-kDa family G xylanases similar to Xyl1. Xyl2 and Xyl3 are 60% and 42% identical, respectively, to Xyl1, and Xyl2 and Xyl3 are 39% identical. XYL1 and XYL2 but not XYL3 mRNAs are present in C. carbonum grown in culture, and XYL1 and XYL3 but not XYL2 mRNAs are present in infected plants. Transformation-mediated gene disruption was used to construct strains mutated in XYL1, XYL2, and XYL3. Xyl1 accounts for most of the total xylanase activity in culture, and disruption of XYL2 or XYL3 does not result in the further loss of any xylanase activity. In particular, the third peak of cationic xylanase activity is still present in a xyl1 xyl2 xyl3 triple mutant, and therefore this xylanase must be encoded by yet a fourth xylanase gene. A minor protein of 22 kDa that can be detected immunologically in the xyl1 mutant disappears in the xyl2 mutant and is therefore proposed to be the product of XYL2. The single xylanase mutants were crossed with each other to obtain multiple xylanase disruptions within the same strain. Strains disrupted in combinations of two and in all three xylanases were obtained. The triple mutant grows at the same rate as the wild type on xylan and on maize cell walls. The triple mutant is still fully pathogenic on maize with regard to lesion size, morphology, and rate of lesion development.
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PMID:Cloning, disruption, and expression of two endo-beta 1, 4-xylanase genes, XYL2 and XYL3, from Cochliobolus carbonum. 890 4

Heteroxylans are major constituents of cell walls in the graminaceous monocotyledons. Degradation of walls in the starchy endosperm of germinated cereal grains is mediated, in part at least, by the action of (1-->4)-beta-xylan endohydrolases (EC 3.2.1.8). Complementary DNAs encoding (1-->4)-beta-xylan endohydrolases from the aleurone layer of germinated barley have been isolated and characterized. Southern blot analyses suggest that the enzymes are derived from a family of 3 or 4 genes, and cDNAs corresponding to two of these genes have been sequenced. The amino acid sequence deduced from one cDNA almost exactly matches the amino acid sequence determined previously from the purified enzyme. This enzyme is designated (1-->4)-beta-xylan endohydrolase isoenzyme X-I. The mature enzyme consists of 395 amino acid residues, has a calculated M(r) of ca. 44600 and an isoelectric point of 6.1, and is likely to adopt an (alpha/beta)8 barrel conformation. The amino acid sequence of the barley (1-->4)-beta-xylan endohydrolase encoded by the other cDNA, which is designated isoenzyme X-II, shows ca. 13% sequence divergence compared with isoenzyme X-I. Both enzymes exhibit sequence and structural similarities with microbial xylanases. Expression of the genes in germinated grain appears to be confined largely to the aleurone layer, and no mRNA transcripts could be detected in young vegetative tissues.
Plant Mol Biol 1996 Sep
PMID:Molecular cloning of cDNAs encoding (1-->4)-beta-xylan endohydrolases from the aleurone layer of germinated barley (Hordeum vulgare). 891 32

Cellulase and xylanase cDNAs were isolated from a cDNA library of the polycentric anaerobic fungus Orpinomyces sp. strain PC-2 constructed in Escherichia coli. The cellulase cDNA (celB) was 1.8 kb long with an open reading frame (ORF) coding for a polypeptide of 471 amino acids, and the xylanase cDNA (xynA) was 1.2 kb long with an ORF encoding a polypeptide of 362 amino acids. Single transcripts of 1.9 kb for celB and 1.5 kb for xynA were detected in total RNA of Orpinomyces grown on Avicel. Genomic DNA regions coding for CelA and XynA were devoid of introns. The enzymes were highly homologous (80 to 85% identity) to the corresponding enzymes of the monocentric anaerobic fungus Neocallimastix patriciarum and, like those, contained in addition to a catalytic domain, a noncatalytic repeated peptide domain (NCRPD). The Orpinomyces xylanase contained one catalytic domain and thus differed from the Neocallimastix xylanase, which had two similar catalytic domains (H. J. Gilbert, G. P. Hazlewood, J. I. Lauie, C. G. Orpin, and G. P. Xue, Mol. Microbiol. 6:2065-2072, 1992). Two peptides corresponding to the catalytic domain and the NCRPD of XynA were synthesized, and antibodies against them were raised and affinity column purified. The antibodies against the catalytic domain peptide reacted specifically with the xylanases of Orpinomyces and Neocallimastix, while the antibodies against the NCRPD reacted with many (at least eight) extracellular proteins of Orpinomyces and Neocallimastix, suggesting that the NCRPD is present in a number of polypeptides.
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PMID:Monocentric and polycentric anaerobic fungi produce structurally related cellulases and xylanases. 902 40

A gene encoding (1-->4)-beta-xylan xylanohydrolase (EC 3.2.1.8) isoenzyme X-I has been isolated from a barley genomic library and the nucleotide sequence of a 2704-bp fragment defined. The gene contains a single intron of 91 bp in the coding region of the mature enzyme and additional introns may be present in the 5'-untranslated region. Expression of the xylanase gene is restricted to the aleurone layer of germinated grain, where the phytohormone gibberellic acid induces both transcriptional activity of the gene and the secretion of active enzyme from the layers. Abscisic acid abolishes the gibberellic acid induction of xylanase gene expression. The hormonal responses are consistent with the presence of promoter sequences, all of which are within 150 bp of the putative transcription start site, that have been implicated as cis-acting elements within gibberellic acid response complexes in plant genes. The elements include a pyrimidine box, CTCTTTCC, together with TAACGAC and TATCCAT boxes. Three genes encode (1-->4)-beta-xylanase isoenzymes in barley and these have been mapped on the barley genome using two doubled haploid populations and seven wheat-barley addition lines. The three xylanase genes are closely linked on the long arm of chromosome 7 (5H). No recombination was detected between the genes in 234 doubled haploid lines. The genes are flanked by the RFLP markers CDO506 on the proximal side and PSR370 at the distal end.
Mol Gen Genet 1997 Feb 20
PMID:Structure, hormonal regulation, and chromosomal location of genes encoding barley (1-->4)-beta-xylan endohydrolases. 906 93

The hyperthermophilic bacterium Thermotoga maritima is capable of gaining metabolic energy utilizing xylan. XynA, one of the corresponding hydrolases required for its degradation, is a 120-kDa endo-1,4-D-xylanase exhibiting high intrinsic stability and a temperature optimum approximately 90 degrees C. Sequence alignments with other xylanases suggest the enzyme to consist of five domains. The C-terminal part of XynA was previously shown to be responsible for cellulose binding (Winterhalter C, Heinrich P, Candussio A, Wich G, Liebl W. 1995. Identification of a novel cellulose-binding domain within the multi-domain 120 kDa Xylanase XynA of the hyperthermophilic bacterium Thermotoga maritima. Mol Microbiol 15:431-444). In order to characterize the domain organization and the stability of XynA and its C-terminal cellulose-binding domain (CBD), the two separate proteins were expressed in Escherichia coli. CBD, because of its instability in its ligand-free form, was expressed as a glutathione S-transferase fusion protein with a specific thrombin cleavage site as linker. XynA and CBD were compared regarding their hydrodynamic and spectral properties. As taken from analytical ultracentrifugation and gel permeation chromatography, both are monomers with 116 and 22 kDa molecular masses, respectively. In the presence of glucose as a ligand, CBD shows high intrinsic stability. Denaturation/renaturation experiments with isolated CBD yield > 80% renaturation, indicating that the domain folds independently. Making use of fluorescence emission and far-UV circular dichroism in order to characterize protein stability, guanidine-induced unfolding of XynA leads to biphasic transitions, with half-concentrations c1/2 (GdmCl) approximately 4 M and > 5 M, in accordance with the extreme thermal stability. At acid pH, XynA exhibits increased stability, indicated by a shift of the second guanidine-transition from 5 to 7 M GdmCl. This can be tentatively attributed to the cellulose-binding domain. Differences in the transition profiles monitored by fluorescence emission and dichroic absorption indicate multi-state behavior of XynA. In the case of CBD, a temperature-induced increase in negative ellipticity at 217 nm is caused by alterations in the environment of aromatic residues that contribute to the far-UV CD in the native state.
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PMID:Xylanase XynA from the hyperthermophilic bacterium Thermotoga maritima: structure and stability of the recombinant enzyme and its isolated cellulose-binding domain. 926 Feb 84

The presence of nutrients in the intestinal lumen is a major factor influencing bacterial colonization in poultry. This study was conducted to investigate the effects of poultry feed on viscosity of intestinal contents and on mucin carbohydrates by comparing jejunal supernatants and the histochemical composition of goblet cells in chicks reared to 5 weeks of age on either a conventional maize-based diet or a wheat-based diet or a wheat diet supplemented with 0.1% xylanase. Regional differences in the distribution of the neutral, carboxylated and sulphated mucins were demonstrated using conventional histochemical techniques, while a panel of lectins was used to study alterations in glycoconjugate synthesis of mucins in chicks fed different diets. 1) Feeding a diet supplemented with xylanase lowered the viscosity but increased the amount of neutral, carboxylated and sulphated mucins in the jejunum. 2) In chicks fed a maize-based diet, neutral mucins increased in the surface and upper crypt goblet cells of the small and large intestines but decreased in the caecum. 3) Feeding a diet supplemented with xylanase modified crypt-surface glycosylation of N-acetylglucosamine residues and resulted in loss of sialic acid residues in the small and large intestines. These results indicate that the constituents of poultry feed, in particular the consumption of a diet supplemented with xylanase, lead to changes in intestinal viscosity and mucin composition which are associated with alterations in the goblet cell glycoconjugates of the chick intestinal tract.
Cell Mol Life Sci 1997 Dec
PMID:The influence of diet on the mucin carbohydrates in the chick intestinal tract. 944 46

Compost is the preferred substrate for growth of the edible fungus Agaricus bisporus. Utilization of compost requires the production of enzymes involved in degradation of lignocellulolytic components. For molecular characterization of these processes we are isolating the encoding genes. By applying heterologous screening techniques, we have cloned such a gene, which is specifically induced on compost encoding an endo-1,4-beta-xylanase (xlnA) belonging to glycosyl hydrolase family 10. The gene encodes a pre-protein of 333 amino acid residues with a predicted molecular mass of 34,946 for the mature protein. The open reading frame is interrupted by ten introns of which introns 5 and 6 are separated by an exon of only two base-pairs. High expression of the xlnA gene was observed in vegetative mycelium grown on sterilized compost while xlnA messengers were not detected in fruit bodies. Addition of glucose or xylose to compost repressed xlnA expression. When glucose-grown colonies were transferred to a medium containing cellulose, xylan or xylose as sole carbon source, the organism responded by expressing xlnA at a high level for a short period. Transfer from glucose to compost yielded a much stronger and constant xlnA induction. A similar pattern of expression was found for the cel3 gene encoding a cellulase, suggesting that these genes are induced by compost-specific factors rather than by the substrates they act upon. Antiserum raised against XLNA protein, which was heterologously expressed in Escherichia coli, detected, when the fungus was grown on compost, an extracellular protein of 33 kDa with endo-xylanase activity.
J Mol Biol 1998 Mar 27
PMID:An endo-1,4-beta-xylanase-encoding gene from Agaricus bisporus is regulated by compost-specific factors. 951 54


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