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Distinct actions by Paenibacillus sp. strain E18 ?-L-arabinofuranosidases and xylanase in xylan degradation.

ABSTRACT: We cloned a Paenibacillus sp. strain E18 5.3-kb xylanolytic gene cluster that contains three open reading frames encoding two family 43 ?-L-arabinofuranosidases (Abf43A and Abf43B) and one family 10 xylanase (XynBE18). The deduced amino acid sequences of Abf43A and Abf43B were at most 68% and 63% identical to those of two putative family 43 proteins from Clostridium sp. strain DL-VIII (EHI98634.1 and EHI98635.1), respectively, but were only 11% identical to each other. Recombinant Abf43A and Abf43B had similar activities at 45°C and pH 6.0 but varied in thermostabilities and substrate specificities. Abf43B was active against only 4-nitrophenyl ?-L-arabinofuranoside, whereas Abf43A acted on 4-nitrophenyl ?-L-arabinofuranoside, wheat arabinoxylan, 4-nitrophenyl ?-D-xylopyranoside, and sugar beet arabinan. The sequential and combined effects on xylan degradation by XynBE18, Abf43A, and Abf43B were characterized. For beechwood, birchwood, and oat spelt xylans as the substrates, synergistic effects were found when XynBE18 and Abf43A or Abf43B were incubated together and when the substrates were first incubated with Abf43A or Abf43B and then with XynBE18. Further high-performance liquid chromatography (HPLC) analysis showed that the amounts of xylobiose and xylose increased sharply in the aforementioned reactions. For water-soluble wheat arabinoxylan as the substrate, Abf43A not only released arabinose but also had a synergistic effect with XynBE18. Synergy may arise as the result of removal of arabinose residues from xylans by ?-L-arabinofuranosidases, which eliminates steric hindrance caused by the arabinose side chains and which allows xylanases to then degrade the xylan backbone, producing short xylooligosaccharides.

SUBMITTER: Shi P

PROVIDER: S-EPMC3592258 | biostudies-literature | 2013 Mar

REPOSITORIES: biostudies-literature

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Distinct actions by Paenibacillus sp. strain E18 α-L-arabinofuranosidases and xylanase in xylan degradation.

Shi Pengjun P Chen Xiaoyan X Meng Kun K Huang Huoqing H Bai Yingguo Y Luo Huiying H Yang Peilong P Yao Bin B

Applied and environmental microbiology 20130118 6

We cloned a Paenibacillus sp. strain E18 5.3-kb xylanolytic gene cluster that contains three open reading frames encoding two family 43 α-L-arabinofuranosidases (Abf43A and Abf43B) and one family 10 xylanase (XynBE18). The deduced amino acid sequences of Abf43A and Abf43B were at most 68% and 63% identical to those of two putative family 43 proteins from Clostridium sp. strain DL-VIII (EHI98634.1 and EHI98635.1), respectively, but were only 11% identical to each other. Recombinant Abf43A and Abf ...[more]

PMID: 23335774

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Project description:Xylans, including methylglucuronoxylans (MeGX(n)) and methylglucuronoarabinoxylans (MeGAXn), are the predominant polysaccharidesin hemicellulose fractions of dicots and monocots available for conversion to biofuels and chemicals. Paenibacillus sp. strain JDR-2 (Pjdr2) efficiently depolymerizes MeGX(n) and MeGAX(n) and assimilates the generated oligosaccharides, resulting in efficient saccharification and subsequent metabolism of these polysaccharides. A xylan utilization regulon encoding a cellassociated GH10 (glycoside hydrolase family 10) endoxylanase, transcriptional regulators, ABC (ATP binding cassette) transporters, an intracellular GH67 -glucuronidase, and other glycoside hydrolases contributes to complete metabolism. This GH10/GH67 system has been proposed to account for preferential utilization of xylans compared to free oligo- and monosaccharides. To identify additional genes contributing to MeGX(n) and MeGAXn utilization, the transcriptome of Pjdr2 has been sequenced following growth on each of these substrates as well as xylose and arabinose. Increased expression of genes with different substrates identified pathways common or unique to the utilization of MeGX(n) or MeGAX(n). Coordinate upregulation of genes comprising the GH10/GH67 xylan utilization regulon is accompanied with upregulation of genes encoding a GH11 endoxylanase and a GH115 -glucuronidase, providing evidence for a novel complementary pathway for processing xylans. Elevated expression of genes encoding a GH43 arabinoxylan arabinofuranohydrolase and an arabinose ABC transporter on MeGAX(n) but not on MeGX(n) supports a process in which arabinose may be removed extracellularly followed by its rapid assimilation.Further development of Pjdr2 for direct conversion of xylans to targeted products or introduction of these systems into fermentative strains of related bacteria may lead to biocatalysts for consolidated bioprocessing of hemicelluloses released from lignocellulose.

Project description:Species in the extremely thermophilic genus Caldicellulosiruptor can degrade unpretreated plant biomass through the action of multimodular glycoside hydrolases. To date, most focus with these bacteria has been on hydrolysis of glucans and xylans, while the biodegradation mechanism for arabinose-based polysaccharides remains unclear. Here, putative ?-l-arabinofuranosidases (AbFs) were identified in Caldicellulosiruptor species by homology to less-thermophilic versions of these enzymes. From this screen, an extracellular XynF was determined to be a key factor in hydrolyzing ?-1,2-, ?-1,3-, and ?-1,5-l-arabinofuranosyl residues of arabinose-based polysaccharides. Combined with a GH11 xylanase (XynA), XynF increased arabinoxylan hydrolysis more than 6-fold compared to the level seen with XynA alone, likely the result of XynF removing arabinofuranosyl side chains to generate linear xylans that were readily degraded. A second AbF, the intracellular AbF51, preferentially cleaved the ?-1,5-l-arabinofuranosyl glycoside bonds within sugar beet arabinan. ?-Xylosidases, such as GH39 Xyl39B, facilitated the hydrolysis of arabinofuranosyl residues at the nonreducing terminus of the arabinose-branched xylo-oligosaccharides by AbF51. These results demonstrate the separate but complementary contributions of extracellular XynF and cytosolic AbF51 in processing the bioconversion of arabinose-containing oligosaccharides to fermentable monosaccharides.IMPORTANCE Degradation of hemicellulose, due to its complex chemical structure, presents a major challenge during bioconversion of lignocellulosic biomass to biobased fuels and chemicals. Degradation of arabinose-containing polysaccharides, in particular, can be a key bottleneck in this process. Among Caldicellulosiruptor species, the multimodular arabinofuranosidase XynF is present in only selected members of this genus. This enzyme exhibited high hydrolysis activity, broad specificity, and strong synergism with other hemicellulases acting on arabino-polysaccharides. An intracellular arabinofuranosidase, AbF51, occurs in all Caldicellulosiruptor species and, in conjunction with xylosidases, processes the bioconversion of arabinose-branched oligosaccharides to fermentable monosaccharides. Taken together, the data suggest that plant biomass degradation in Caldicellulosiruptor species involves extracellular XynF that acts synergistically with other hemicellulases to digest arabino-polysaccharides that are subsequently transported and degraded further by intracellular AbF51 to produce short-chain arabino sugars.

Dataset Information

Distinct actions by Paenibacillus sp. strain E18 ?-L-arabinofuranosidases and xylanase in xylan degradation.

Publications

Distinct actions by Paenibacillus sp. strain E18 α-L-arabinofuranosidases and xylanase in xylan degradation.

Similar Datasets

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