Arabinoxylan-degrading enzyme system of the fungus Aspergillus awamori: purification and properties of an alpha-L-arabinofuranosidase

Long-term fungal inoculation of Ficus sycomorus and Tectona grandis woods with Aspergillus flavus and Penicillium chrysogenum

In the current study, two molds, Aspergillus flavus (ACC# LC325160) and Penicillium chrysogenum (ACC# LC325162) were inoculated into two types of wood to be examined using scanning electron microscopy-energy dispersive X-ray (SEM-EDX) and computerized tomography (CT) scanning. Ficus sycomorus, a non-durable wood, and Tectona grandis, a durable wood, were the two wood blocks chosen, and they were inoculated with the two molds and incubated for 36 months at an ambient temperature of 27 ± 2 °C and 70 ± 5% relative humidity (RH). The surface and a 5-mm depth of inoculated wood blocks were histologically evaluated using SEM and CT images. The results showed that A. flavus and P. chrysogenum grew enormously on and inside of F. sycomorus wood blocks, but T. grandis wood displayed resistance to mold growth. The atomic percentages of C declined from 61.69% (control) to 59.33% in F. sycomorus wood samples inoculated with A. flavus while O increased from 37.81 to 39.59%. P. chrysogenum caused the C and O atomic percentages in F. sycomorus wood to drop to 58.43%, and 26.34%, respectively. C with atomic percentages in Teak wood's C content fell from 70.85 to 54.16%, and 40.89%, after being inoculated with A. flavus and P. chrysogenum. The O atomic percentage rose from 28.78 to 45.19% and 52.43%, when inoculated with A. flavus and P. chrysogenum, respectively. Depending on how durable each wood was, The examined fungi were able to attack the two distinct types of wood in various deterioration patterns. T. grandis wood overtaken by the two molds under study appears to be a useful material for a variety of uses.

The Role of Arabinogalactan Type II Degradation in Plant-Microbe Interactions

Arabinogalactans (AGs) are structural polysaccharides of the plant cell wall. A small proportion of the AGs are associated with hemicellulose and pectin. Furthermore, AGs are associated with proteins forming the so-called arabinogalactan proteins (AGPs), which can be found in the plant cell wall or attached through a glycosylphosphatidylinositol (GPI) anchor to the plasma membrane. AGPs are a family of highly glycosylated proteins grouped with cell wall proteins rich in hydroxyproline. These glycoproteins have important and diverse functions in plants, such as growth, cellular differentiation, signaling, and microbe-plant interactions, and several reports suggest that carbohydrate components are crucial for AGP functions. In beneficial plant-microbe interactions, AGPs attract symbiotic species of fungi or bacteria, promote the development of infectious structures and the colonization of root tips, and furthermore, these interactions can activate plant defense mechanisms. On the other hand, plants secrete and accumulate AGPs at infection sites, creating cross-links with pectin. As part of the plant cell wall degradation machinery, beneficial and pathogenic fungi and bacteria can produce the enzymes necessary for the complete depolymerization of AGs including endo-β-(1,3), β-(1,4) and β-(1,6)-galactanases, β-(1,3/1,6) galactanases, α-L-arabinofuranosidases, β-L-arabinopyranosidases, and β-D-glucuronidases. These hydrolytic enzymes are secreted during plant-pathogen interactions and could have implications for the function of AGPs. It has been proposed that AGPs could prevent infection by pathogenic microorganisms because their degradation products generated by hydrolytic enzymes of pathogens function as damage-associated molecular patterns (DAMPs) eliciting the plant defense response. In this review, we describe the structure and function of AGs and AGPs as components of the plant cell wall. Additionally, we describe the set of enzymes secreted by microorganisms to degrade AGs from AGPs and its possible implication for plant-microbe interactions.

A Glycoside Hydrolase Family 62 A-L-Arabinofuranosidase from Trichoderma Reesei and Its Applicable Potential during Mashing

Arabinoxylan is the second most abundant component in the endosperm cell wall of barley and it has been shown to have negative effects on the viscosity and filtration rate of wort and beer. In this study, a glycoside hydrolase (GH) family 62 α-L-arabinofuranosidase (AFase), termed as TrAbf62A, was purified from the culture filtrate of Trichoderma reesei CICC 41495 by a combined chromatographic method. The preferred substrates of the purified TrAbf62A were soluble, highly substituted arabinoxylan oligosaccharides and polymers, similar to the type found in barley grain. TrAbf62A exhibited activity towards oligomeric and polymeric arabinoxylans, as well as colorimetric arabinose-based substrates, thus meeting the criteria to be classified as a type B AFase. TrAbf62A released mainly arabinose and xylose from soluble wheat arabinoxylan, thus indicating a dual lytic enzyme activity. Supplementation of TrAbf62A during mashing, with a loading of 12 mU/g malt, resulted in a 36.3% decrease in arabinoxylan polymer content, a 5.6% reduction in viscosity, and finally, a 22.1% increase in filtration rate. These results revealed that TrAbf62A has a high potential value in improving lautering performance during mashing.

Improved growth of Lactobacillus bulgaricus and Streptococcus thermophilus as well as Increased antioxidant activity by biotransforming litchi pericarp polysaccharide with Aspergillus awamori

This study was conducted to increase the bioactivity of litchi pericarp polysaccharides (LPPs) biotransformed by Aspergillus awamori. Compared to the non-A. awamori-fermented LPP, the growth effects of A. awamori-fermented LPP on Lactobacillus bulgaricus and Streptococcus thermophilus were four and two times higher after 3 days of fermentation, respectively. Increased 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity and DNA protection activity of litchi pericarp polysaccharides were also achieved after A. awamori fermentation. Moreover, the relative content of glucose and arabinose in LPP after fermentation decreased from 58.82% to 22.60% and from 18.82% to 10.09%, respectively, with a concomitant increase in the relative contents of galactose, rhamnose, xylose, and mannose. Furthermore, lower molecular weight polysaccharides were obtained after A. awamori fermentation. It can be concluded that A. awamori was effective in biotransforming LPP into a bioactive mixture with lower molecular weight polysaccharides and higher antioxidant activity and relative galactose content.

Enhanced DPPH radical scavenging activity and DNA protection effect of litchi pericarp extract by Aspergillus awamori bioconversion

BACKGROUND

Litchi (Litchi chinensis Sonn.) pericarp is a major byproduct which contains a significant amount of polyphenol. This study was designed to biotransformation litchi pericarp extract (LPE) by Aspergillus awamori to produce more bioactive compounds with stronger antioxidant activities.

RESULTS

The study exhibited that the 2,2-diphenyl-1-picrylhydrazyl radical scavenging activities significantly (p < 0.05) increased from 15.53% to 18.23% in the water-extracted fraction and from 25.41% to 36.82% in the ethyl acetate-extracted fraction. Application of DNA cleavage assay further demonstrated the enhanced protection effect of the fermented phenolics on DNA damage. It is also noted that the water-extracted fraction of the fermented LPE possessed a much stronger capacity than the ethyl acetate-extracted fraction to prevent from damage of supercoiled DNA. Interestingly, it was found that some new compounds such as catechin and quercetin appeared after of A. awamori fermentation of LPE, which could account for the enhanced antioxidant activity.

CONCLUSION

The DPPH radical scavenging activity and DNA protection effect of LPE were increased by Aspergillus awamori bioconversion while some compounds responsible for the enhanced antioxidant activity were identified. This study provided an effective way of utilizing fruit pericarp as a readily accessible source of the natural antioxidants in food industry and, thus, extended the application area such as fruit by-products.

Purification and functional characterization of a novel alpha-L-arabinofuranosidase from Bifidobacterium longum B667

The gene encoding a novel alpha-L-arabinofuranosidase from Bifidobacterium longum B667, abfB, was cloned and sequenced. The deduced protein had a molecular mass of about 61 kDa, and analysis of its amino acid sequence revealed significant homology and conservation of different catalytic residues with alpha-L-arabinofuranosidases belonging to family 51 of the glycoside hydrolases. Regions flanking the gene comprised two divergently transcribed open reading frames coding for hypothetical proteins involved in sugar metabolism. A histidine tag was introduced at the C terminus of AbfB, and the recombinant protein was overexpressed in Lactococcus lactis under control of the tightly regulated, nisin-inducible nisA promoter. The enzyme was purified by nickel affinity chromatography. The molecular mass of the native protein, as determined by gel filtration, was about 260 kDa, suggesting a homotetrameric structure. AbfB was active at a broad pH range (pH 4.5 to 7.5) and at a broad temperature range (20 to 70 degrees C), and it had an optimum pH of 6.0 and an optimum temperature of 45 degrees C. The enzyme seemed to be less thermostable than most previously described arabinofuranosidases and had a half-life of about 3 h at 55 degrees C. Chelating and reducing agents did not have any effect on its activity, but the presence of Cu(2+), Hg(2+), and Zn(2+) markedly reduced enzymatic activity. The protein exhibited a high level of activity with p-nitrophenyl alpha-L-arabinofuranoside, with apparent K(m) and V(max) values of 0.295 mM and 417 U/mg, respectively. AbfB released L-arabinose from arabinan, arabinoxylan, arabinobiose, arabinotriose, arabinotetraose, and arabinopentaose. No endoarabinanase activity was detected. These findings suggest that AbfB is an exo-acting enzyme and may play a role, together with other glycosidases, in the degradation of L-arabinose-containing polysaccharides.

Purification and partial characterization of alpha-L-arabinofuranosidase produced by Thermomonospora fusca

Thermomonospora fusca produced a relatively high level of alpha-L-arabinofuranosidase when growing on oat spelt xylan as the main carbon and energy source. The enzyme exhibited maximum relative activity (0.136 U/g protein) at pH 9.0 with 54 and 55% activity remaining at pH of 4.5 and 11.0, respectively. The apparent Km value for the crude alpha-L-arabinofuranosidase preparation was 180 mumol/L 4-nitrophenyl alpha-L-arabinofuranoside; the upsilon lim value was the release of 40 mumol/L 4-nitrophenol per min. Enzyme activity was eluted as a single peak (HPLC gel filtration chromatography) corresponding to molar mass of approximately 92 kDa. Native electrophoresis of crude cell lysate confirmed the presence of a single active intracellular alpha-L-arabinofuranosidase component. SDS-PAGE of this enzyme, developed as zymogram, did not demonstrate any activity; denaturing gel was stained and a protein band of relative molar mass of 46 kDa was revealed. Isoelectric focusing of a purified alpha-L-arabinofuranosidase yielded a single protein band for the corresponding activity zone with pI 7.9. The enzyme was purified approximately 21-fold the mean overall yield was about 16%.

Aspergillus enzymes involved in degradation of plant cell wall polysaccharides

Degradation of plant cell wall polysaccharides is of major importance in the food and feed, beverage, textile, and paper and pulp industries, as well as in several other industrial production processes. Enzymatic degradation of these polymers has received attention for many years and is becoming a more and more attractive alternative to chemical and mechanical processes. Over the past 15 years, much progress has been made in elucidating the structural characteristics of these polysaccharides and in characterizing the enzymes involved in their degradation and the genes of biotechnologically relevant microorganisms encoding these enzymes. The members of the fungal genus Aspergillus are commonly used for the production of polysaccharide-degrading enzymes. This genus produces a wide spectrum of cell wall-degrading enzymes, allowing not only complete degradation of the polysaccharides but also tailored modifications by using specific enzymes purified from these fungi. This review summarizes our current knowledge of the cell wall polysaccharide-degrading enzymes from aspergilli and the genes by which they are encoded.

Purification and substrate specificities of two alpha-L-arabinofuranosidases from Aspergillus awamori IFO 4033

alpha-L-Arabinofuranosidases I and II were purified from the culture filtrate of Aspergillus awamori IFO 4033 and had molecular weights of 81,000 and 62,000 and pIs of 3.3 and 3.6, respectively. Both enzymes had an optimum pH of 4.0 and an optimum temperature of 60 degreesC and exhibited stability at pH values from 3 to 7 and at temperatures up to 60 degrees C. The enzymes released arabinose from p-nitrophenyl-alpha-L-arabinofuranoside, O-alpha-L-arabinofuranosyl-(1-->3)-O-beta-D-xylopyranosyl-(1-->4)-D-x ylopyranose, and arabinose-containing polysaccharides but not from O-beta-D-xylopyranosyl-(1-->2)-O-alpha-L-arabinofuranosyl-(1-->3)-O-b eta-D-xylopyranosyl-(1-->4)-O-beta-D-xylopyranosyl-(1-->4)-D-xylopyra nose. alpha-L-Arabinofuranosidase I also released arabinose from O-beta-D-xylopy-ranosyl-(1-->4)-[O-alpha-L-arabinofuranosyl- (1-->3)]- O-beta-D-xylopyranosyl-(1-->4)-D-xylopyranose. However, alpha-L-arabinofuranosidase II did not readily catalyze this hydrolysis reaction. alpha-L-Arabinofuranosidase I hydrolyzed all linkages that can occur between two alpha-L-arabinofuranosyl residues in the following order: (1-->5) linkage > (1-->3) linkage > (1-->2) linkage. alpha-L-Arabinofuranosidase II hydrolyzed the linkages in the following order: (1-->5) linkage > (1-->2) linkage > (1-->3) linkage. alpha-L-Arabinofuranosidase I preferentially hydrolyzed the (1-->5) linkage of branched arabinotrisaccharide. On the other hand, alpha-L-arabinofuranosidase II preferentially hydrolyzed the (1-->3) linkage in the same substrate. alpha-L-Arabinofuranosidase I released arabinose from the nonreducing terminus of arabinan, whereas alpha-L-arabinofuranosidase II preferentially hydrolyzed the arabinosyl side chain linkage of arabinan.