The PcAxy43B is a modular protein comprising a catalytic domain of glycoside hydrolase family 43 (GH43), a family 6 carbohydrate-binding module (CBM6) and a family 36 carbohydrate-binding module (CBM36) and found to be a novel multifunctional xylanolytic enzyme from Paenibacillus curdlanolyticus B-6. This enzyme exhibited α-L-arabinofuranosidase, endo-xylanase and β-D-xylosidase activities. α-L-Arabinofuranosidase of PcAxy43B revealed the new property of GH43, which released arabinose from the short-chain arabinoxylo-oligosaccharide (AXOS) and cereal arabinoxylan, and from both sides of the xylose residues of AXOS, which usually obstruct the action of xylanolytic enzymes. The PcAxy43B liberated series of xylo-oligosaccharides (XOSs) from birchwood xylan and xylohexaose, indicating that PcAxy43B exhibited endo-xylanase activity. The PcAxy43B produced xylose from xylobiose and reacted with p -nitrophenyl-β-D-xylopyranoside as a result of β-xylosidase activity. The PcAxy43B effectively released arabinose together with XOSs and xylose from the highly arabinosyl-substituted rye arabinoxylan. Moreover, PcAxy43B showed significant synergistic action with a trifunctional endo-xylanase/β-xylosidase/α-L-arabinofuranosidase PcAxy43A and an endo-xylanase Xyn10C from the strain B-6, in which almost all products produced from rye arabinoxylan by these combined enzymes were arabinose and xylose. In addition, the presence of CBM36 was found to be necessary for the endo-xylanase property of PcAxy43B. The PcAxy43B is capable of hydrolysing untreated cereal biomass, corn hull and rice straw into XOSs and xylose. Hence, PcAxy43B, the significant accessory multifunctional xylanolytic enzyme, is a potential candidate for application in the saccharification of cereal biomass. IMPORTANCE Enzymatic saccharification of cereal biomass is a strategy for the production of fermented sugars from low-price raw materials. In the present study, PcAxy43B from P. curdlanolyticus B-6 was found to be a novel multifunctional α-L-arabinofuranosidase/endo-xylanase/β-D-xylosidase enzyme of the glycoside hydrolase family 43. It is effective in releasing arabinose, xylose and XOSs from the highly arabinosyl-substituted rye arabinoxylan, which is usually resistant to hydrolysis by xylanolytic enzymes. Moreover, almost all products produced from rye arabinoxylan by the combination of PcAxy43B with trifunctional xylanolytic enzyme PcAxy43A and endo-xylanase Xyn10C from the strain B-6 were arabinose and xylose, which can be used to produce several value-added products. In addition, PcAxy43B is capable of hydrolysing untreated cereal biomass into XOSs and xylose. Thus, PcAxy43B is an important multifunctional xylanolytic enzyme with high potential in biotechnology.

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