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Query: UNIPROT:P06889 (Mol)
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A cDNA (xynA), encoding xylanase A (XYLA), was isolated from a cDNA library, derived from mRNA extracted from the rumen anaerobic fungus, Neocallimastix patriciarum. Recombinant XYLA, purified from Escherichia coli harbouring xynA, had a M(r) of 53,000 and hydrolysed oat-spelt xylan to xylobiose and xylose. The enzyme did not hydrolyse any cellulosic substrates. The nucleotide sequence of xynA revealed a single open reading frame of 1821 bp coding for a protein of M(r) 66,192. The predicted primary structure of XYLA comprised an N-terminal signal peptide followed by a 225-amino-acid repeated sequence, which was separated from a tandem 40-residue C-terminal repeat by a threonine/proline linker sequence. The large N-terminal reiterated regions consisted of distinct catalytic domains which displayed similar substrate specificities to the full-length enzyme. The reiterated structure of XYLA suggests that the enzyme was derived from an ancestral gene which underwent two discrete duplications. Sequence comparison analysis revealed significant homology between XYLA and bacterial xylanases belonging to cellulase/xylanase family G. One of these homologous enzymes is derived from the rumen bacterium Ruminococcus flavefaciens. The homology observed between XYLA and a rumen prokaryote xylanase could be a consequence of the horizontal transfer of genes between rumen prokaryotes and lower eukaryotes, either when the organisms were resident in the rumen, or prior to their colonization of the ruminant. It should also be noted that Neocallimastix XYLA is the first example of a xylanase which consists of reiterated sequences. It remains to be established whether this is a common phenomenon in other rumen fungal plant cell wall hydrolases.
Mol Microbiol 1992 Aug
PMID:Homologous catalytic domains in a rumen fungal xylanase: evidence for gene duplication and prokaryotic origin. 140 48

Single crystals of the catalytic domain of Cex, an exo-beta-1,4-glucanase and beta-1,4-xylanase from the cellulolytic bacterium Cellulomonas fimi, have been grown in the presence of polyethylene glycol 4000 using the vapour diffusion technique. The crystals, which diffract to better than 2.0 A resolution, belong to space group P4(1)2(1)2 or P4(3)2(1)2 and have cell constants: a = b = 88.21 A, c = 81.10 A; alpha = beta = gamma = 90 degrees.
J Mol Biol 1992 Nov 20
PMID:Crystallization and preliminary X-ray diffraction analysis of the catalytic domain of Cex, an exo-beta-1,4-glucanase and beta-1,4-xylanase from the bacterium Cellulomonas fimi. 145 71

The xylanase gene from Cryptococcus albidus contains seven introns. Genomic and cDNA clones under the control of the CaMV 35S promoter were transferred into tobacco plants using Agrobacterium-mediated cell transformation. The genes were transcribed and the mRNAs were amplified by the polymerase chain reaction using primers on each side of the intron region. About 90% of the amplification products from plants transformed with the genomic clone corresponded to the size of the pre-mRNA (1.2 kb) and 10% represented the spliced product (0.85 kb). The 0.85 kb fragment was cloned and sequenced and the result indicated that the introns from the xylanase gene were accurately spliced by the plant cells.
Plant Mol Biol 1992 Feb
PMID:The xylanase introns from Cryptococcus albidus are accurately spliced in transgenic tobacco plants. 153 22

The nucleotide sequence of the xynA gene of Ruminococcus flavefaciens 17 was determined and found to consist of a 2862bp open reading frame beginning with a TTG start codon. The predicted product, XYLA, consisted of distinct amino-terminal (A) and carboxy terminal (C) domains (248 amino acids, including a putative signal sequence, and 332 amino acids, respectively) linked by a repetitive sequence (B, 374 amino acids) extraordinarily rich in asparagine (45%) and glutamine (26%) residues. Domains A and C were shown to be capable of expressing xylanase activity independently of each other when suitably truncated derivatives of the xynA coding region were expressed as lacZ fusions. The activities associated with the two domains were shown to differ with respect to the average size of hydrolysis products formed from oat-spelt xylan, with domain C releasing relatively more xylose and domain A more xylo-oligosaccharides. The amino acid sequence of domain A of XYLA closely resembled that of the Bacillus pumilus xynA enzyme (45% identical residues). On the other hand domain C showed significant similarity (33% to 40% identical residues) to a different group of bacterial xylanases and exoglucanases exemplified by the Caldocellum saccharolyticum xynA and celB products. The xynA product is, therefore, a bifunctional enzyme having two dissimilar catalytic domains capable of acting on xylan.
Mol Microbiol 1992 Apr
PMID:A bifunctional xylanase encoded by the xynA gene of the rumen cellulolytic bacterium Ruminococcus flavefaciens 17 comprises two dissimilar domains linked by an asparagine/glutamine-rich sequence. 158 21

A gene encoding a basic-type pathogenesis-related protein from Nicotiana tabacum (prb-1b) was cloned, sequenced and characterized. It contains an open reading frame of 179 amino acids that is ca. 65% homologous with the acidic PR-1 class of pathogenesis-related proteins and 87% homologous with a different basic-type PR-1 gene. In the light, physiological levels of ethylene rapidly (1 h) induced basic, but not acidic-type, PR-1 transcript. Additional elicitors acting via ethylene, such as alpha-aminobutyric acid, were shown to induce basic- and acidic-type PR-1 transcript accumulation in a light-dependent manner. In contrast, xylanase, an ethylene-independent elicitor, induced transcript accumulation of basic- and acidic-type PR-1 in a light-independent manner. Dark-induced accumulation of basic PR-1 transcript occurred at night in greenhouse-grown plants and, to a greater extent, in continuously dark-treated plants. The novel dark regulation may point to additional nonpathogenesis-related roles for these genes in plant-environment interactions.
Plant Mol Biol 1992 Jul
PMID:Dark-induced accumulation of a basic pathogenesis-related (PR-1) transcript and a light requirement for its induction by ethylene. 162 72

The cloning, expression and nucleotide sequence of a 3 kb DNA segment on pLS206 containing a xylanase gene (xynB) from Butyrivibrio fibrisolvens H17c was investigated. The open reading frame (ORF) of 1905 bp encoded a xylanase of 635 amino acid residues (Mr 73156). At least 850 bp at the 3' end of the gene could be deleted without loss of xylanase activity. The deduced amino acid sequence was confirmed by purifying the enzyme and subjecting it to N-terminal amino acid sequence analysis. In Escherichia coli C600 (pLS206) cells the xylanase was localized in the cytoplasm. Its optimum pH for activity was between pH 5.4 and 6, and optimum temperature 55 degrees C. The primary structure of the xylanase showed a significant level of identity with a cellobiohydrolase/endoglucanase of Caldocellum saccharolyticum, as well as with the xylanases of the alkaliphilic Bacillus sp. strain C-125, B. fibrisolvens strain 49, and Pseudomonas fluorescens subsp. cellulosa.
Mol Gen Genet 1991 Aug
PMID:Cloning, sequencing and expression of a gene encoding a 73 kDa xylanase enzyme from the rumen anaerobe Butyrivibrio fibrisolvens H17c. 190 24

The substrate specificity of an endoglucanase (EGB) from Pseudomonas fluorescens subspecies cellulosa was determined. The enzyme was most active against barley beta-glucan, but showed significant activity against amorphous and crystalline cellulose. EGB was purified to homogeneity by affinity chromatography with crystalline cellulose (Avicel). The Mr of the purified enzyme was 50,000, which is in good agreement with the size of EGB deduced from the nucleotide sequence of the celB gene, coding for EGB. The N-terminal region of the mature form of EGB showed strong homology to another endoglucanase and to a xylanase expressed by the same organism; homologous sequences included highly conserved serine-rich regions. Truncated forms of celB, in which the gene sequence encoding the conserved domain had been deleted, directed the synthesis of a functional endoglucanase that did not bind to crystalline cellulose. This indicates that the conserved region of endoglucanases and xylanases expressed by P. fluorescens subsp. cellulosa constitutes a cellulose-binding domain, which is distinct from the active centre. The possible role of this substrate-binding region is discussed.
Mol Microbiol 1990 May
PMID:The N-terminal region of an endoglucanase from Pseudomonas fluorescens subspecies cellulosa constitutes a cellulose-binding domain that is distinct from the catalytic centre. 211 93

The complete nucleotide sequence of the xynA gene coding for a xylanase (XYLA) expressed by Pseudomonas fluorescens subspecies cellulosa, has been determined. The structural gene consists of an open reading frame of 1833 bp followed by a TAA stop codon. Confirmation of the nucleotide sequence was obtained by comparing the predicted amino acid sequence with that derived by N-terminal analysis of purified forms of the xylanase. The signal peptide present at the N terminus of mature XYLA closely resembles signal peptides of other secreted proteins. Truncated forms of the xylanase gene, in which the sequence encoding the N-terminal signal peptide had been deleted, still expressed coli. XYLA contains domains which are homologous to an endoglucanase expressed by the same organism. These structures include serine-rich sequences. Bal31 deletions of xynA revealed the extent to which these conserved sequences, in XYLA, were essential for xylanase activity. Downstream of the TAA stop codon is a G + C-rich region of dyad symmetry (delta G = 24 kcal) characteristic of E. coli Rho-independent transcription terminators.
Mol Microbiol 1989 Sep
PMID:Conserved serine-rich sequences in xylanase and cellulase from Pseudomonas fluorescens subspecies cellulosa: internal signal sequence and unusual protein processing. 250 68

The xylan-degrading enzyme xylanase, from Bacillus pumilus IPO, has been crystallized. The crystals are monoclinic, space group P21 with a = 40.8 A, b = 66.8 A, c = 34.7 A and beta = 103.0 degrees. The asymmetric unit contains one molecule of Mr 22,500. The crystals diffract to at least 2.5 A resolution, and they are suitable for X-ray crystal structure analysis at high resolution.
J Mol Biol 1987 Jan 05
PMID:Crystallization and preliminary X-ray studies of Bacillus pumilus IPO xylanase. 358 24

A 20,000 Mr xylanase from Trichoderma harzianum has been purified and crystallized from 20% (w/v) saturated ammonium sulphate solutions. The unit cell is orthorhombic, space group P2(1)2(1)2(1), with unit cell lengths a = 44.2 A, b = 94.1 A, c = 51.6 A. Data from native crystals and several potential heavy-atom derivatives have been collected. An X-ray analysis to at least 2.8 A resolution appears to be feasible.
J Mol Biol 1987 Apr 20
PMID:Crystallization and preliminary X-ray diffraction study of a xylanase from Trichoderma harzianum. 365 7


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