Cellulase (CEL) presently constitutes a major group of industrial enzyme based on its diverse ranges of utilization. Apart from such current and well-established applications-as in cotton processing, paper recycling, detergent formulation, juice extraction, and animal feed additives-their uses in agricultural biotechnology and bioenergy have been exploited. Supplementation of CELs to accelerate decomposition of plant residues in soil results in improved soil fertility. So far, applying CELs/antagonistic cellulolytic fungi to crops has shown to promote plant growth performance, including enhanced seed germination and protective effects. Their actions are believed mainly to trigger plant defense mechanisms and/or to act as biocontrol agents that mediate disease suppression. However, the exact interaction between the enzymes/fungi and plants has not been clearly elucidated. Under mild conditions, removal of plant cell wall polysaccharides by CELs for protoplast preparation results in reduced protoplast damage and increased viability and yields. CELs have recently shown great potential in enzyme aid extraction of bioactive compounds from plant materials before selective extraction through enhancing release of target molecules, especially those associated with the wall matrix. To date, attempts have been made to formulate CEL preparation for cellulosic-based bioethanol production. The high cost of CELs has created a bottleneck, resulting in an uneconomic production process. The utilization of low-cost carbohydrates, strain improvement, and gene manipulations has been alternatively aimed at reducing the cost of CEL production. In this review, we focus on and discuss current knowledge of CELs and their applications in agriculture, biotechnology, and bioenergy.
The axy43A gene encoding the intracellular trifunctional xylanolytic enzyme from Paenibacillus curdlanolyticus B-6 was cloned and expressed in Escherichia coli. Recombinant PcAxy43A consisting of a glycoside hydrolase family 43 and a family 6 carbohydrate-binding module exhibited endo-xylanase, -xylosidase, and arabinoxylan arabinofuranohydrolase activities. PcAxy43A hydrolyzed xylohexaose and birch wood xylan to release a series of xylooligosaccharides, indicating that PcAxy43A contained endo-xylanase activity. PcAxy43A exhibited -xylosidase activity toward a chromogenic substrate, p-nitrophenyl--D-xylopyranoside, and xylobiose, while it preferred to hydrolyze long-chain xylooligosaccharides rather than xylobiose. In addition, surprisingly, PcAxy43A showed arabinoxylan arabinofuranohydrolase activity; that is, it released arabinose from both singly and doubly arabinosylated xylose,Moreover, the combination of PcAxy43A and P. curdlanolyticus B-6 endo-xylanase Xyn10C greatly improved the efficiency of xylose and arabinose production from the highly substituted rye arabinoxylan, suggesting that these two enzymes function synergistically to depolymerize arabinoxylan. Therefore, PcAxy43A has the potential for the saccharification of arabinoxylan into simple sugars for many applications.
IMPORTANCEIn this study, the glycoside hydrolase 43 (GH43) intracellular multifunctional endo-xylanase, -xylosidase, and arabinoxylan arabinofuranohydrolase (AXH) from P. curdlanolyticus B-6 were characterized. Interestingly, PcAxy43A AXH showed a new property that acted on both the C(O)-2 and C(O)-3 positions of xylose residues doubly substituted with arabinosyl, which usually obstruct the action of xylanolytic enzymes. Furthermore, the studies here show interesting properties for the processing of xylans from cereal grains, particularly rye arabinoxylan, and show a novel relationship between PcAxy43A and endo-xylanase Xyn10C from strain B-6, providing novel metabolic potential for processing arabinoxylans into xylose and arabinose.
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