Comparison of endolytic hydrolases that depolymerise 1,4-β-D-mannan, 1,5-α-L-arabinan and 1,4-β-D-galactan.
McCleary, B. V. (1991). “Enzymes in Biomass Conversion”, (M. E. Himmel and G. F. Leatham, Eds.), ACS Symposium Series 460, Chapter 34, pp. 437-449. American Chemical Society, Washington.
Hydrolysis of mannan-type polysaccharides by β-mannanase is dependent on substitution on and within the main-chain as well as the source of the β-mannanase employed. Characterisation of reaction products can be used to define the sub-site binding requirements of the enzymes as well as the fine-structures of the polysaccharides. Action of endo-arabinanase and endo-galactanase on arabinans and arabinogalactans is described. Specific assays for endo-arabinanase and arabinan (in fruit-juice concentrates) are reported.
Measurement of endo-1,4-β-D-xylanase.
McCleary, B. V. (1992). “Xylans and Xylanases”, (J. Visser, G. Beldman, M. A. Kusters-van Someron and A. G. J. Voragen, Eds.), Progress in Biotechnology Vol. 7, Elsevier, Science Publishers B. V., pp. 161-169.
Various procedures for the measurement of xylanase in fermentation broths, commercial enzyme mixtures, bread improver mixtures and feed samples are described. Problems associated with the routine use of reducing-sugar based methods axe highlighted and the advantages and limitations of viscometric and dye-labelled substrate procedures for measurement of trace levels of activity in feed samples are discussed.
Measurement of polysaccharide degrading enzymes using chromogenic and colorimetric substrates.
McCleary, B. V. (1991). Chemistry in Australia, 58, 398-401.
Enzymic degradation of carbohydrates is of major significance in the industrial processing of cereals and fruits. In the production of beer, barley is germinated under well defined conditions (malting) to induce maximum enzyme synthesis with minimum respiration of reserve carbohydrates. The grains are dried and then extracted with water under controlled conditions. The amylolytic enzymes synthesized during malting, as well as those present in the original barley, convert the starch reserves to fermentable sugars. Other enzymes act on the cell wall polysaccharides, mixed-linkage β-glucan and arabinoxylan, reducing the viscosity and thus aiding filtration, and reducing the possibility of subsequent precipitation of polymeric material. In baking, β-amylase and α-amylase give controlled degradation of starch to fermentable sugars so as to sustain yeast growth and gas production. Excess quantities of α-amylase in the flour result in excessive degradation of starch during baking which in turn gives a sticky crumb texture and subsequent problems with bread slicing. Juice yield from fruit pulp is significantly improved if cell-wall degrading enzymes are used to destroy the three-dimensional structure and water binding capacity of the pectic polysaccharide components of the cell walls. Problems of routine and reliable assay of carbohydrate degrading enzymes in the presence of high levels of sugar compounds are experienced with such industrial process.
Optimising the response.
Acamovic, T. & McCleary, B. V. (1996). Feed Mix, 4, 14-19.
A fine balance exists between enzyme activity and the adverse effects associated with feed processing. Accurate estimation of enzyme activity in the feed is a pre-requisite to optimising the response.
Cloning and characterization of arabinoxylan arabinofuranohydrolase-D3 (AXHd3) from Bifidobacterium adolescentis DSM20083.
Van den Broek, L. A. M., Lloyd, R. M., Beldman, G., Verdoes, J. C., McCleary, B. V. & Voragen, A. G. J. (2005). Applied Microbiology and Biotechnology, 67(5), 641-647.
Arabinoxylan arabinofuranohydrolase-D3 (AXHd3) from Bifidobacterium adolescentis releases only C3-linked arabinose residues from double-substituted xylose residues. A genomic library of B. adolescentis DSM20083 was screened for the presence of the axhD3 gene. Two plasmids were identified containing part of the axhD3 gene. The nucleotide sequences were combined and three open reading frames (ORFs) were found. The first ORF showed high homology with xylanases belonging to family 8 of the glycoside hydrolases and this gene was designated xylA. The second ORF was the axhD3 gene belonging to glycoside hydrolase family 43. The third (partial) ORF coded for a putative carboxylesterase. The axhD3 gene was cloned and expressed in Escherichia coli. Several substrates were employed in the biochemical characterization of recombinant AXHd3. The enzyme showed the highest activity toward wheat arabinoxylan oligosaccharides. In addition, β-xylanase from Trichoderma sp. was able to degrade soluble wheat arabinoxylan polymer to a higher extent, after pretreatment with recombinant AXHd3. Arabinoxylan oligosaccharides incubated with a combination of recombinant AXHd3 and an α-L-arabinofuranosidase from Aspergillus niger did not result in a higher maximal release of arabinose than incubation with these enzymes separately.
Recombinant expression and characterization of XynD from Bacillus subtilis subsp. subtilis ATCC 6051: a GH 43 arabinoxylan arabinofuranohydrolase.
Bourgois, T. M., Van Craeyveld, V., Van Campenhout, S., Courtin, C. M., Delcour, J. A., Robben, J. & Volckaert, G. (2007). Applied Microbiology and Biotechnology, 75(6), 1309-1317.
The complete genome sequence of Bacillus subtilis reveals that sequences encoding several hemicellulases are co-localised with a gene (xynD) encoding a putative family 43 glycoside hydrolase that has not yet been characterised. In this work, xynD has been isolated from genomic DNA of B. subtilis subsp. subtilis ATCC 6051 and cloned for cytoplasmatic expression in Escherichia coli. Recombinant XynD (rXynD) was purified using ion-exchange chromatography and gel permeation chromatography. The enzyme had a molecular mass of approximately 52 kDa, a p/above 9.0 and releases α-L-arabinose from arabinoxylo-oligosaccharides as well as arabinoxylan polymers with varying degree of substitution. Using para-nitrophenyl-α-L-arabinofuranoside as substrate, maximum activity was observed at pH 5.6 and 45°C. The enzyme retained its activity over a large pH range, while activity was lost after pre-incubation above 50°C. Gas–liquid chromatography and proton nuclear magnetic resonance spectrometry analysis indicated that rXynD specifically releases arabinofuranosyl groups from mono-substituted C-(O)-2 and C-(O)-3 xylopyranosyl residues on the xylan backbone. As rXynD did not display endoxylanase, xylosidase or arabinanase activity and was inactive on arabinan, we conclude that this enzyme is best described as an arabinoxylan arabinofuranohydrolase.
Variability in the release of free and bound hydroxycinnamic acids from diverse malted barley (Hordeum vulgare L.) cultivars during wort production.
Vanbeneden, N., Gils, F., Delvaux, F. & Delvaux, F. R. (2007). Journal of Agricultural and Food Chemistry, 55(26), 11002-11010.
Volatile phenols have long been recognized as important flavor contributors to the aroma of various alcoholic beverages. The two main flavor-active volatile phenols in beer are 4-vinylguaiacol and 4-vinylphenol. They are the decarboxylation products of the precursors ferulic acid and p-coumaric acid, respectively, which are released during the brewing process, mainly from malt. In this study, the variability in the release of free and ester-bound hydroxycinnamic acids from nine malted barley (Hordeum vulgare L.) varieties during wort production was investigated. A large variability between different barley malts and their corresponding worts was observed. Differences were also found between free ferulic acid levels from identical malt varieties originating from different malt houses. During mashing, free hydroxycinnamic acids in wort are both water-extracted and enzymatically released by cinnamoyl esterase activity. Esterase activities clearly differ between different barley malt varieties. Multiple linear regression analysis showed that the release of ferulic acid during mashing did not depend only on the barley malt esterase activity but also on the amount of ester-bound ferulic acid initially present in the wort and on its endoxylanase activity. The study demonstrates the importance of selecting a suitable malt variety as the first means of controlling the final volatile phenol levels in beer.
Variability in the structure of rye flour alkali-extractable arabinoxylans.
Verwimp, T., Van Craeyveld, V., Courtin, C. M. & Delcour, J. A. (2007). Journal of Agricultural and Food Chemistry, 55(5), 1985-1992.
The variability in rye flour alkali-extractable arabinoxylan (AE-AX) structures was examined by extensive fractionation and enzymic degradation studies. AX were isolated from destarched rye water-unextractables by sequential extraction with saturated barium hydroxide solution, water, 1.0 M sodium hydroxide, and water. The isolated AE-AX contained ca. 51% AX with an arabinose to xylose (A/X) ratio of 0.71. Fractionation of the isolated AE-AX by ethanol precipitation yielded a range of AE-AX fractions containing AX molecules with different A/X ratios and substitution patterns. Degradation of these structurally different AE-AX fractions by an Aspergillus aculeatus endoxylanase (XAA) and a Bacillus subtilis endoxylanase (XBS) resulted in AX fragments with various structural features. Further fractionation of the degraded AE-AX fractions by ethanol precipitation showed that a strong correlation exists between the structural features of the AX fragments, that is, average degree of polymerization (DP) of the xylan backbone, A/X ratio, and substitution pattern. Results indicated that the rye flour AE-AX consist of a continuum of structures rather than of two types of AX or two types of regions in the AX molecule.
Impact of wheat flour-associated endoxylanases on arabinoxylan in dough after mixing and resting.
Dornez, E., Gebruers, K., Cuyvers, S., Delcour, J. A. & Courtin, C. M. (2007). Journal of Agricultural and Food Chemistry, 55(17), 7149-7155.
The impact of varying levels of endoxylanase activity in wheat flour on arabinoxylan (AX) in mixed and rested dough was studied using eight industrially milled wheat flour fractions with varying endoxylanase activity levels. Analysis of the levels of reducing end xylose (RX) and solubilized AX (S-AX) formed during mixing and resting and their correlation with the endoxylanase activity in the flour milling fractions showed that solubilization of AX during the mixing phase is mainly due to mechanical forces, while solubilization of AX during resting is caused by endoxylanase activity. Moreover, solubilization of AX during the dough resting phase is more outspoken than that during the mixing phase. Besides endoxylanase activity, there were significant xylosidase and arabinofuranosidase activities during the dough resting phase. The results indicate that wheat flour-associated endoxylanases can alter part of the AX in dough, thereby changing their functionality in bread making and potentially affecting dough and end product properties.
An accurate normalization strategy for RT-qPCR in Hypocrea jecorina (Trichoderma reesei).
Steiger, M. G., Mach, R. L. & Mach-Aigner, A. R. (2010). Journal of Biotechnology, 145(1), 30-37.
Hypocrea jecorina is an important, filamentous fungus due to its effective production of hydrolytic enzymes. Gene expression studies provide deeper insight into environment sensing and cellular response mechanisms. Reverse transcription-quantitative PCR is a gene-specific and powerful tool to measure even minor changes in mRNA composition. An accurate normalization strategy is absolutely necessary for appropriate interpretation of reverse transcription-quantitative PCR results. One frequently applied strategy is the usage of a reference gene. Adequate reference genes for Hypocrea have not been published so far. By using the NormFinder and geNorm softwares, we evaluated the most stable genes amongst six potential reference genes in 34 samples from diverse cultivation conditions. Under those experimental conditions, sar1 encoding for a small GTPase was found to be the most stable gene, whereas act encoding for actin was not amongst the best validated ones. The influence of the reference system on the expression data is demonstrated by analysis of two target genes, encoding for the Xylanase regulator 1 and for Xylanase II. We further validated obtained xylanase 2 transcription rates with the corresponding enzyme activity.
Xylanases from microbial origin induce syrup formation in dough.
De Schryver, P., Sesena, S., Decaigny, B., Van de Wiele, T., Verstraete, W. & Boon, N. (2008). Journal of Cereal Science, 47(1), 18-28.
Syrup formation in refrigerated doughs is a problem since it reduces the doughs’ shelf life. Microbial exogenous xylanases associated with wheat kernels were found to play a role in this syruping phenomenon. Using xylanase-producing microorganisms isolated from wheat kernels, we investigated their potency to induce syruping in dough. Growth of the fungal xylanase producer Fusarium sp. (102 colony forming units (CFU)/g dough) and the bacterial xylanase producer Paenibacillus sp. (104 CFU/g dough) in synthetic media and their respective addition to wheat dough could not bring about a significant amount of syruping. However, when these species were grown on moist wheat kernels and an extract of these kernels containing both the organisms and its xylanases was made and added to dough, intensive syruping was noted. This effect was primarily attributed to the xylanases present in the extract. These findings suggest that the involvement of xylanase-producing microorganisms in the syruping phenomenon is situated prior to harvest. Additional quantitative analyses of microbial biomass present on wheat kernels revealed that the fungi in particular could be correlated to higher microbial exogenous xylanase activities on wheat. Our results indicate that the syruping is linked to fungal xylanase production on the wheat kernels in the field.
Transcriptional regulation of xyr1, encoding the main regulator of the xylanolytic and cellulolytic enzyme system in Hypocrea jecorina.
Mach-Aigner, A. R., Pucher, M. E., Steiger, M. G., Bauer, G. E., Preis, S. J. & Mach, R. L. (2008). Applied and Environmental Microbiology, 74(21), 6554-6562.
In Hypocrea jecorina, Xyr1 (xylanase regulator 1) is the main transcription activator of hydrolase-encoding genes, such as xyn1, xyn2, bxl1, cbh1, cbh2, egl1, and bgl1. Even though Xyr1 mediates the induction signal for all these genes derived from various inducing carbon sources and compounds, xyr1 transcription itself is not inducible by any of these substances. However, cultivation on glucose as the carbon source provokes carbon catabolite repression of xyr1 transcription mediated by Cre1. In addition, xyr1 transcription is repressed by the specific transcription factor Ace1. Moreover, Xyr1 is permanently available in the cell, and no de novo synthesis of this factor is needed for a first induction of xyn1 transcription. The constitutive expression of xyr1 leads to a significant elevation/deregulation of the xyn1, xyn2, and bxl1 transcription compared to what is seen for the parental strain. Overall, the corresponding xylanolytic enzyme activities are clearly elevated in a constitutively xyr1-expressing strain, emphasizing this factor as an auspicious target for genetically engineered strain improvement.
A screening method for endo-β-1,4-xylanase substrate selectivity.
Moers, K., Courtin, C. M., Brijs, K. & Delcour, J. A. (2003). Analytical Biochemistry, 319(1), 73-77.
Endoxylanase (EC 18.104.22.168) substrate selectivity, i.e., its relative activity toward water-unextractable arabinoxylan (WU-AX) and water-extractable arabinoxylan (WE-AX) substrates, is important for its functionality in biotechnological processes such as bread-making and gluten starch separation. A screening method for rapidly determining said substrate selectivity was developed. Endoxylanase activity toward WU-AX was estimated by incubation of insoluble chromogenic substrate with a range of enzyme concentrations in microtiter plates, followed by colorimetric measurement of the dye released in the supernatant. A similar approach using soluble substrate and ethanol precipitation of unhydrolysed AX fragments was used to estimate enzyme activity toward WE-AX. A substrate selectivity factor was defined as the ratio of enzyme activity toward insoluble substrate over enzyme activity toward soluble substrate. A Bacillus subtilis and an Aspergillus aculeatus endoxylanase, known to have widely varying relative rates of hydrolysis of WU-AX and WE-AX, varied most in their substrate selectivity, while the endoxylanases of Aspergillus niger, Trichoderma longibrachiatum, and Trichoderma viride displayed intermediate such relative activities.
Xyr1 receives the lactose induction signal and regulates lactose metabolism in Hypocrea jecorina.
Stricker, A., R., Steiger, M., G. & Mach, R., L. (2007). FEBS Letters, 581(21), 3915-3920.
This study reports the vital regulatory influence of Xyr1 (xylanase regulator 1) on the transcription of hydrolytic enzyme-encoding genes and hydrolase formation on lactose in Hypocrea jecorina. While the transcription of the xyr1 gene itself is achieved by release of carbon catabolite repression, the transcript formation of xyr1 (xylanase 1) is regulated by an additional induction mechanism mediated by lactose. Xyr1 has an important impact on lactose metabolism by directly activating xyr1 (xylose reductase 1) transcription and indirectly influencing transcription of bga1 (β-galactosidase 1). The latter is achieved by regulating the conversion of D-galactose to the inducing carbon source galactitol.
Multi-carbohydrase and phytase supplementation improves growth performance and liver insulin receptor sensitivity in broiler chickens fed diets containing full-fat rapeseed.
Józefiak, D., Ptak, A., Kaczmarek, S., Maćkowiak, P., Sassek, M. & Slominski, B. A. (2010). Poultry Science, 89(9), 1939-1946.
The effect of a combination of carbohydrase and phytase enzymes on growth performance, insulin-like growth factor 1 gene expression, insulin status, and insulin receptor sensitivity in broiler chickens fed wheat-soybean meal diets containing 6% (starter) and 12% (grower-finisher) of full-fat rapeseed (canola type; low glucosinolate, low erucic acid) from 1 to 42 d of age was studied. A total of 510 one-day-old male broiler chickens were randomly assigned to 3 dietary treatments, with 17 pens per treatment and 10 birds per pen. The dietary treatments consisted of a control diet and P- and Ca-deficient diets supplemented with either phytase (500 U/kg) or a combination of phytase and a multi-carbohydrase enzyme (Superzyme OM). The diets were pelleted at 78°C and were fed ad libitum throughout the starter (9 d), grower (18 d), and finisher (15 d) phases of the experiment. Over the entire trial, growth performance of birds fed the phytase-supplemented diet did not differ from birds fed the control diet. The use of phytase in combination with a multicarbohydrase enzyme improved (P = 0.007) the feed conversion ratio from 1.90 to 1.84. Insulin liver receptor sensitivity increased by 9.3 and 12.3% (P = 0.004) for the phytase- and the carbohydrase-phytase-supplemented diets, respectively. There was no effect of phytase alone or carbohydrase and phytase supplementation on total plasma cholesterol, high-density lipoprotein cholesterol, and blood glucose levels. However, low-density lipoprotein cholesterol decreased (P = 0.007) for the phytase-carbohydrase treatment. Gene expression of insulin-like growth factor 1 tended to decrease by 32% (P = 0.083) after phytase-carbohydrase supplementation. The combination of carbohydrase and phytase enzymes may serve as an attractive means of facilitating nutrient availability for digestion and thus enhance the feeding value of wheat-soybean meal-based diets containing full-fat rapeseed. However, the extent to which the effects of enzyme addition on insulin receptors are associated with growth performance of broiler chicken requires further research.