• Journal of Microbiology and Biotechnology
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• v.25 no.2
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• pp.227-233
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• 2015

Two recombinant arabinosyl hydrolases, α-_L-arabinofuranosidase from Geobacillus sp. KCTC 3012 (GAFase) and endo-(1,5)-α-_L-arabinanase from Bacillus licheniformis DSM13 (BlABNase), were overexpressed in Escherichia coli, and their synergistic modes of action against sugar beet (branched) arabinan were investigated. Whereas GAFase hydrolyzed 35.9% of _L-arabinose residues from sugar beet (branched) arabinan, endo-action of BlABNase released only 0.5% of _L-arabinose owing to its extremely low accessibility towards branched arabinan. Interestingly, the simultaneous treatment of GAFase and BlABNase could liberate approximately 91.2% of _L-arabinose from arabinan, which was significantly higher than any single exo-enzyme treatment (35.9%) or even stepwise exo- after endo-enzyme treatment (75.5%). Based on their unique modes of action, both exo- and endo-arabinosyl hydrolases can work in concert to catalyze the hydrolysis of arabinan to _L-arabinose. At the early stage in arabinan degradation, exo-acting GAFase could remove the terminal arabinose branches to generate debranched arabinan, which could be successively hydrolyzed into arabinooligosaccharides via the endo-action of BlABNase. At the final stage, the simultaneous actions of exo- and endo-hydrolases could synergistically accelerate the _L-arabinose production with high conversion yield.

• Journal of Microbiology and Biotechnology
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• v.29 no.1
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• pp.37-43
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• 2019

The gene encoding an ${\alpha}-{\text\tiny{L}}-arabinofuranosidase$ (BvAF) GH51 from Bacillus velezensis FZB42 was cloned and expressed in Escherichia coli. The corresponding open reading frame consists of 1,491 nucleotides which encode 496 amino acids with the molecular mass of 56.9 kDa. BvAF showed the highest activity against sugar beet (branched) arabinan in 50 mM sodium acetate buffer (pH 6.0) at $45^{\circ}C$. However, it could hardly hydrolyze debranched arabinan and arabinoxylans. The time-course hydrolyses of branched arabinan and arabinooligosaccharides (AOS) revealed that BvAF is a unique exo-hydrolase producing exclusively ${\text\tiny{L}}-arabinose$. BvAF could cleave ${\alpha}-(1,2)-$ and/or ${\alpha}-(1,3)-{\text\tiny{L}}-arabinofuranosidic$ linkages of the branched substrates to produce the debranched forms of arabinan and AOS. Although the excessive amount of BvAF could liberate ${\text\tiny{L}}-arabinose$ from linear AOS, it was extremely lower than that on branched AOS. In conclusion, BvAF is the arabinan-specific exo-acting ${\alpha}-{\text\tiny{L}}-arabinofuranosidase$ possessing high debranching activity towards ${\alpha}-(1,2)-$ and/or ${\alpha}-(1,3)-linked$ branches of arabinan, which can facilitate the successive degradation of arabinan by $endo-{\alpha}-(1,5)-{\text\tiny{L}}-arabinanase$.

• Journal of Microbiology and Biotechnology
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• v.17 no.11
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• pp.1782-1788
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• 2007

Cellulosomes in Clostridium cellulovorans are assembled by the interaction between the repeated cohesin domains of a scaffolding protein (CbpA) and the dockerin domain of enzyme components. In this study, we determined the synergistic effects on cellulosic and hemicellulosic substrates by three different recombinant mini-cellulosomes containing either endoglucanase EngB or endoxylanase XynA bound to mini-CbpA with one cohesin domain (mini-CbpAl), two cohesins (mini-CbpA12), or four cohesins (mini-CbpAl234). The assembly of EngB or XynA with mini-CbpA increased the activity against carboxymethyl cellulose, acid-swollen cellulose, Avicel, xylan, and com fiber 1.1-1.8-fold compared with that for the corresponding enzyme alone. A most distinct improvement was shown with com fiber, a natural substrate containing xylan, arabinan, and cellulose. However, there was little difference in activity between the three different mini-cellulosomes when the cellulosomal enzyme concentration was held constant regardless of the copy number of cohesins in the cellulosome. A synergistic effect was observed when the enzyme concentration was increased to be proportional to the number of cohesins in the mini-cellulosome. The highest degree of synergy was observed with mini-CbpAl234 (1.8-fold) and then mini-CbpAl2 (1.3-fold), and the lowest synergy was observed with mini-CbpAl (1.2-fold) when Avicel was used as the substrate. As the copy number of cohesin was increased, there was more synergy. These results indicate that the clustering effect (physical enzyme proximity) of the enzyme within the mini-cellulosome is one of the important factors for efficient degradation of plant cell walls.