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Evidence for temporal regulation of the two Pseudomonas cellulosa xylanases belonging to glycoside hydrolase family 11.

ABSTRACT: Pseudomonas cellulosa is a highly efficient xylan-degrading bacterium. Genes encoding five xylanases, and several accessory enzymes, which remove the various side chains that decorate the xylan backbone, have been isolated from the pseudomonad and characterized. The xylanase genes consist of xyn10A, xyn10B, xyn10C, xyn10D, and xyn11A, which encode Xyn10A, Xyn10B, Xyn10C, Xyn10D, and Xyn11A, respectively. In this study a sixth xylanase gene, xyn11B, was isolated which encodes a 357-residue modular enzyme, designated Xyn11B, comprising a glycoside hydrolase family 11 catalytic domain appended to a C-terminal X-14 module, a homologue of which binds to xylan. Localization studies showed that the two xylanases with glycoside hydrolase family (GH) 11 catalytic modules, Xyn11A and Xyn11B, are secreted into the culture medium, whereas Xyn10C is membrane bound. xyn10C, xyn10D, xyn11A, and xyn11B were all abundantly expressed when the bacterium was cultured on xylan or beta-glucan but not on medium containing mannan, whereas glucose repressed transcription of these genes. Although all of the xylanase genes were induced by the same polysaccharides, temporal regulation of xyn11A and xyn11B was apparent on xylan-containing media. Transcription of xyn11A occurred earlier than transcription of xyn11B, which is consistent with the predicted mode of action of the encoded enzymes. Xyn11A, but not Xyn11B, exhibits xylan esterase activity, and the removal of acetate side chains is required for xylanases to hydrolyze the xylan backbone. A transposon mutant of P. cellulosa in which xyn11A and xyn11B were inactive displayed greatly reduced extracellular but normal cell-associated xylanase activity, and its growth rate on medium containing xylan was indistinguishable from wild-type P. cellulosa. Based on the data presented here, we propose a model for xylan degradation by P. cellulosa in which the GH11 enzymes convert decorated xylans into substituted xylooligosaccharides, which are then hydrolyzed to their constituent sugars by the combined action of cell-associated GH10 xylanases and side chain-cleaving enzymes.

SUBMITTER: Emami K

PROVIDER: S-EPMC135193 | biostudies-literature | 2002 Aug

REPOSITORIES: biostudies-literature

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Evidence for temporal regulation of the two Pseudomonas cellulosa xylanases belonging to glycoside hydrolase family 11.

Emami Kaveh K Nagy Tibor T Fontes Carlos M G A CM Ferreira Luis M A LM Gilbert Harry J HJ

Journal of bacteriology 20020801 15

Pseudomonas cellulosa is a highly efficient xylan-degrading bacterium. Genes encoding five xylanases, and several accessory enzymes, which remove the various side chains that decorate the xylan backbone, have been isolated from the pseudomonad and characterized. The xylanase genes consist of xyn10A, xyn10B, xyn10C, xyn10D, and xyn11A, which encode Xyn10A, Xyn10B, Xyn10C, Xyn10D, and Xyn11A, respectively. In this study a sixth xylanase gene, xyn11B, was isolated which encodes a 357-residue modula ...[more]

PMID: 12107129

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Project description:Xylanases play a crucial role in the degradation of xylan in both terrestrial and marine environments. The endoxylanase XynB from the marine bacterium Glaciecola mesophila KMM 241 is a modular enzyme comprising a long N-terminal domain (NTD) (E44 to T562) with xylan-binding ability and a catalytic domain (CD) (T563 to E912) of glycoside hydrolase family 8 (GH8). In this study, the long NTD is confirmed to contain three different functional regions, which are NTD1 (E44 to D136), NTD2 (Y137 to A193), and NTD3 (L194 to T562). NTD1, mainly composed of eight ?-strands, functions as a new type of carbohydrate-binding module (CBM), which has xylan-binding ability but no sequence similarity to any known CBM. NTD2, mainly forming two ?-helices, contains one of the ?-helices of the catalytic domain's (?/?)6 barrel and therefore is essential for the activity of XynB, although it is far away from the catalytic domain in sequence. NTD3, next to the catalytic domain in sequence, is shown to be helpful in maintaining the thermostability of XynB. Thus, XynB represents a kind of xylanase with a new domain architecture. There are four other predicted glycoside hydrolase sequences with the same domain architecture and high sequence identity (?80%) with XynB, all of which are from marine bacteria. Phylogenetic analysis shows that XynB and these homologs form a new group in GH8, representing a new class of marine bacterial xylanases. Our results shed light on xylanases, especially marine xylanases.IMPORTANCE Xylanases play a crucial role in natural xylan degradation and have been extensively used in industries such as food processing, animal feed, and kraft pulp biobleaching. Some marine bacteria have been found to secrete xylanases. Characterization of novel xylanases from marine bacteria has significance for both the clarification of xylan degradation mechanisms in the sea and the development of new enzymes for industrial application. With G. mesophila XynB as a representative, this study reveals a new group of the GH8 xylanases from marine bacteria, which have a distinct domain architecture and contain a novel carbohydrate-binding module. Thus, this study offers new knowledge on marine xylanases.

Project description:BACKGROUND: The rumen harbors a complex microbial ecosystem for efficient hydrolysis of plant polysaccharides which are the main constituent of the diet. Xylanase is crucial for hemicellulose hydrolysis and plays an important role in the plant cell wall degradation. Xylanases of ruminal strains were widely studied, but few studies have focused on their diversity in rumen microenvironment. METHODOLOGY/PRINCIPAL FINDINGS: We explored the genetic diversity of xylanases belonging to two major glycosyl hydrolase families (GH 10 and 11) in goat rumen contents by analyzing the amplicons generated with two degenerate primer sets. Fifty-two distinct GH 10 and 35 GH 11 xylanase gene fragments (similarity <95%) were retrieved, and most had low identities with known sequences. Based on phylogenetic analysis, all GH 10 xylanase sequences fell into seven clusters, and 88.5% of them were related to xylanases from Bacteroidetes. Five clusters of GH 11 xylanase sequences were identified. Of these, 85.7% were related to xylanases from Firmicutes, and 14.3% were related to those of rumen fungi. Two full-length xylanase genes (one for each family) were directly cloned and expressed in Escherichia coli. Both the recombinant enzymes showed substantial xylanase activity, and were purified and characterized. Combined with the results of sheep rumen, Bacteroidetes and Firmicutes are the two major phyla of xylan-degrading microorganisms in rumen, which is distinct from the representatives of other environments such as soil and termite hindgut, suggesting that xylan-degrading microorganisms are environment specific. CONCLUSION/SIGNIFICANCE: The numerous new xylanase genes suggested the functional diversity of xylanase in the rumen microenvironment which may have great potential applications in industry and agriculture. The phylogenetic diversity and different distributions of xylanase genes will help us understand their roles in plant cell wall degradation in the rumen microenvironment.

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Dataset Information

Evidence for temporal regulation of the two Pseudomonas cellulosa xylanases belonging to glycoside hydrolase family 11.

Publications

Evidence for temporal regulation of the two Pseudomonas cellulosa xylanases belonging to glycoside hydrolase family 11.

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