The resistance of cellulases and xylanases to proteolytic inactivation

Expression, characterization, and activity optimization of a novel cellulase from the thermophilic bacteria Cohnella sp. A01

Cellulases are hydrolytic enzymes with wide scientific and industrial applications. We described a novel cellulase, CelC307, from the thermophilic indigenous Cohnella sp. A01. The 3-D structure of the CelC307 was predicted by comparative modeling. Docking of CelC307 with specific inhibitors and molecular dynamic (MD) simulation revealed that these ligands bound in a non-competitive manner. The CelC307 protein was purified and characterized after recombinant expression in Escherichia coli (E. coli) BL21. Using CMC 1% as the substrate, the thermodynamic values were determined as K_m 0.46 mM, k_cat 104.30 × 10^-3 (S^-1), and k_cat/K_m 226.73 (M^-1 S^-1). The CelC307 was optimally active at 40 °C and pH 7.0. The culture condition was optimized for improved CelC307 expression using Plackett-Burman and Box-Behnken design as follows: temperature 20 °C, pH 7.5, and inoculation concentration with an OD₆₀₀ = 1. The endoglucanase activity was positively modulated in the presence of Na⁺, Li⁺, Ca²⁺, 2-mercaptoethanol (2-ME), and glycerol. The thermodynamic parameters calculated for CelC307 confirmed its inherent thermostability. The characterized CelC307 may be a suitable candidate for various biotechnological applications.

An individual alginate lyase is effective in the disruption of Laminaria digitata recalcitrant cell wall

In the present study, 199 pre-selected Carbohydrate-Active enZymes (CAZymes) and sulfatases were assessed, either alone or in combination, to evaluate their capacity to disrupt Laminaria digitata cell wall, with the consequent release of interesting nutritional compounds. A previously characterized individual alginate lyase, belonging to the family 7 of polysaccharide lyases (PL7) and produced by Saccharophagus degradans, was shown to be the most efficient in the in vitro degradation of L. digitata cell wall. The alginate lyase treatment, compared to the control, released up to 7.11 g/L of reducing sugars (p < 0.001) and 8.59 mmol/100 g dried alga of monosaccharides (p < 0.001), and reduced cell wall fluorescence intensity by 39.1% after staining with Calcofluor White (p = 0.001). The hydrolysis of gel-forming polymer alginate by the alginate lyase treatment could prevent the trapping of fatty acids and release beneficial monounsaturated fatty acids, particularly 18:1c9 (p < 0.001), to the extracellular medium. However, no liberation of proteins (p > 0.170) or pigments (p > 0.070) was observed. Overall, these results show the ability of an individual alginate lyase, from PL7 family, to partially degrade L. digitata cell wall under physiological conditions. Therefore, this CAZyme can potentially improve the bioavailability of L. digitata bioactive compounds for monogastric diets, with further application in feed industry.

A two-enzyme constituted mixture to improve the degradation of Arthrospira platensis microalga cell wall for monogastric diets

The main goal of this study was to test a rational combination of pre‐selected carbohydrate‐active enzymes (CAZymes) and sulphatases, individually or in combination, in order to evaluate its capacity to disrupt Arthrospira platensis cell wall, allowing the release of its valuable nutritional bioactive compounds. By the end, a two‐enzyme constituted mixture (Mix), composed by a lysozyme and a α‐amylase, was incubated with A. platensis suspension. The microalga cell wall disruption was evaluated through the amount of reducing sugars released from the cell wall complemented with the oligosaccharide profile by HPLC. An increase of the amount of reducing sugars up to 2.42 g/L in microalgae treated with the Mix relative to no treatment (p < .05), as well as a 7‐fold increase of oligosaccharides amount (p < .001), were obtained. With resort of fluorescence microscopy, a 36% reduction of fluorescence intensity (p < .001) was observed using Calcofluor White staining. In the supernatant, the Mix caused a 1.34‐fold increase in protein content (p = .018) relative to the control. Similarly, n‐6 polyunsaturated fatty acids (PUFA) (p = .007), in particular 18:2n‐6 (p = .016), monounsaturated fatty acids (MUFA) (p = .049) and chlorophyll a (p = .025) contents were higher in the supernatant of microalgae treated with the enzyme mixture in relation to the control. Taken together, these results point towards the disclosure of a novel two‐enzyme mixture able to partial degrade A. platensis cell wall, improving its nutrients bioavailability for monogastric diets with the cost‐effective advantage use of microalgae in animal feed industry.

Glycosylation effects on the structure and dynamics of a full-length Cel7A cellulase

Fungi cellulases are used to degrade cellulose-containing biomass for bioethanol production. Industrial cellulases such as Cel7A from Trichoderma reesei (TrCel7A) are critical in this process. Thus, the understanding of structure and dynamics is crucial for engineering variants with improved cellulolytic activity. This cellulase consists of two domains connected by a flexible and highly glycosylated linker. However, the linker flexibility has hindered the determination of Cel7A complete structure. Herein, based on atomic and sparse data, we applied integrative modelling to build a model of the complete enzyme structure. Next, through simulations, we studied the glycosylation effects on the structure and dynamics of a solubilized TrCel7A. Essential dynamics analysis showed that O-glycosylation in the linker led to the stabilization of protein overall dynamics. O-linked glycans seem to restrict protein dihedral angles distribution in this region, selecting more elongated conformations. Besides the reduced flexibility, functional interdomain motions occurred in a more concerted way in the glycosylated system. In contrast, in the absence of glycosylation, we observed vast conformational plasticity with the functional domains frequently collapsing. We report here evidence that targeting Cel7A linker flexibility by point mutations including modification of glycosylation sites could be a promising design strategy to improve cellulase activity.

Novel combination of feed enzymes to improve the degradation of Chlorella vulgaris recalcitrant cell wall

In this study, a rational combination of 200 pre-selected Carbohydrate-Active enzymes (CAZymes) and sulfatases were tested, individually or combined, according to their ability to degrade Chlorella vulgaris cell wall to access its valuable nutritional compounds. The disruption of microalgae cell walls by a four-enzyme mixture (Mix) in comparison with the control, enabled to release up to 1.21 g/L of reducing sugars (p < 0.001), led to an eight-fold increase in oligosaccharides release (p < 0.001), and reduced the fluorescence intensity by 47% after staining with Calcofluor White (p < 0.001). The Mix treatment was successful in releasing proteins (p < 0.001), some MUFA (p < 0.05), and the beneficial 18:3n-3 fatty acid (p < 0.05). Even if no variation was detected for chlorophylls (p > 0.05), total carotenoids were increased in the supernatant (p < 0.05) from the Mix treatment, relative to the control. Taken together, these results indicate that this four-enzyme Mix displays an effective capacity to degrade C. vulgaris cell wall. Thus, these enzymes may constitute a good approach to improve the bioavailability of C. vulgaris nutrients for monogastric diets, in particular, and to facilitate the cost-effective use of microalgae by the feed industry, in general.

Polysaccharide degradation systems of the saprophytic bacterium Cellvibrio japonicus

Study of recalcitrant polysaccharide degradation by bacterial systems is critical for understanding biological processes such as global carbon cycling, nutritional contributions of the human gut microbiome, and the production of renewable fuels and chemicals. One bacterium that has a robust ability to degrade polysaccharides is the Gram-negative saprophyte Cellvibrio japonicus. A bacterium with a circuitous history, C. japonicus underwent several taxonomy changes from an initially described Pseudomonas sp. Most of the enzymes described in the pre-genomics era have also been renamed. This review aims to consolidate the biochemical, structural, and genetic data published on C. japonicus and its remarkable ability to degrade cellulose, xylan, and pectin substrates. Initially, C. japonicus carbohydrate-active enzymes were studied biochemically and structurally for their novel polysaccharide binding and degradation characteristics, while more recent systems biology approaches have begun to unravel the complex regulation required for lignocellulose degradation in an environmental context. Also included is a discussion for the future of C. japonicus as a model system, with emphasis on current areas unexplored in terms of polysaccharide degradation and emerging directions for C. japonicus in both environmental and biotechnological applications.

Role of pectinolytic enzymes identified in Clostridium thermocellum cellulosome

The cloning, expression and characterization of three cellulosomal pectinolytic enzymes viz., two variants of PL1 (PL1A and PL1B) and PL9 from Clostridium thermocellum was carried out. The comparison of the primary sequences of PL1A, PL1B and PL9 revealed that these proteins displayed considerable sequence similarities with family 1 and 9 polysaccharide lyases, respectively. PL1A, PL1B and PL9 are the putative catalytic domains of protein sequence ABN54148.1 and ABN53381.1 respectively. These two protein sequences also contain putative carbohydrate binding module (CBM) and type-I dockerin. The associated putative CBM of PL1A showed strong homology with family 6 CBMs while those of PL1B and PL9 showed homology with family 35 CBMs. Recombinant derivatives of these three enzymes showed molecular masses of approximately 34 kDa, 40 kDa and 32 kDa for PL1A, PL1B and PL9, respectively. PL1A, PL1B and PL9 displayed high activity toward polygalacturonic acid and pectin (up to 55% methyl-esterified) from citrus fruits. However, PL1B showed relatively higher activity towards 55% and 85% methyl-esterified pectin (citrus). PL1A and PL9 showed higher activity on rhamnogalacturonan than PL1B. Both PL1A and PL9 displayed maximum activity at pH 8.5 with optimum temperature of 50°C and 60°C respectively. PL1B achieved highest activity at pH 9.8, under an optimum temperature of 50°C. PL1A, PL1B and PL9 all produced two or more unsaturated galacturonates from pectic substrates as displayed by TLC analysis confirming that they are endo-pectate lyase belonging to family 1 and 9, respectively. This report reveals that pectinolytic activity displayed by Clostridium thermocellum cellulosome is coordinated by a sub-set of at least three multi-modular enzymes.

Characterization of Sphingomonas sp. JB13 exo-inulinase: a novel detergent-, salt-, and protease-tolerant exo-inulinase

A glycoside hydrolase family 32 exo-inulinase gene was cloned from Sphingomonas sp. JB13 and expressed in Escherichia coli BL21 (DE3). The purified recombinant enzyme (rInuAJB13) showed an apparently optimal activity at pH 5.5 and 55 °C and remained activity at 10-70 °C. The addition of most metal ions and chemical reagents showed little or no effect (retaining more than 76.5 % activity) on the enzyme activity, notably the addition of surfactants SDS, CTAB, Tween 80, and Triton X-100. Most local liquid detergents, including Balin, Walch, Ariel, Tide, Tupperware, and Bluemoon, also showed little or no effect (retaining more than 77.8 % activity) on the enzyme activity. rInuAJB13 exhibited 135.3-163.6 % activity at the NaCl concentration of 1.0-4.5 M. After incubation with up to 57.0 mg mL(-1) trypsin and 90.0 mg mL(-1) proteinase K at 37 °C for 60 min (pH 7.2), rInuAJB13 retained more than 80 % of its initial activity. The enzyme presents a high proportion (28.0 %) of amino acid residues G, A, and V. This paper is the first to report a detergent-, salt-, and protease-tolerant exo-inulinase.

Board-invited review: Opportunities and challenges in using exogenous enzymes to improve ruminant production

The ability of ruminants to convert plant biomass unsuitable for human consumption into meat and milk is of great societal and agricultural importance. However, the efficiency of this process is largely dependent on the digestibility of plant cell walls. Supplementing ruminant diets with exogenous enzymes has the potential to improve plant cell wall digestibility and thus the efficiency of feed utilization. Understanding the complexity of the rumen microbial ecosystem and the nature of its interactions with plant cell walls is the key to using exogenous enzymes to improve feed utilization in ruminants. The variability currently observed in production responses can be attributed to the array of enzyme formulations available, their variable activities, the level of supplementation, mode of delivery, and the diet to which they are applied as well as the productivity level of the host. Although progress on enzyme technologies for ruminants has been made, considerable research is still required if successful formulations are to be developed. Advances in DNA and RNA sequencing and bioinformatic analysis have provided novel insight into the structure and function of rumen microbial populations. Knowledge of the rumen microbial ecosystem and its associated carbohydrases could enhance the likelihood of achieving positive responses to enzyme supplementation. The ability to sequence microbial genomes represents a valuable source of information in terms of the physiology and function of both culturable and unculturable rumen microbial species. The advent of metagenomic, metatranscriptomic, and proteomic techniques will further enhance our understanding of the enzymatic machinery involved in cell wall degradation and provide a holistic view of the microbial community and the complexities of plant cell wall digestion. These technologies should provide new insight into the identification of exogenous enzymes that act synergistically with the rumen microbial populations that ultimately dictate the efficiency of feed digestion.

Levels of endogenous β-glucanase activity in barley affect the efficacy of exogenous enzymes used to supplement barley-based diets for poultry

To improve the nutritive value of barley-based diet for broilers, 2 experiments using 2 different barley lots were performed to evaluate the capacity of a mesophilic cellulase when fused to a β-glucan specific family 11 carbohydrate-binding module. The data revealed that the recombinant β-glucanase derivatives were not appropriate for feed supplementation because of a lack of stability at acidic pH levels. However, under the same experimental conditions, a commercial enzyme mixture improved the nutritive value of 1 of the cereal lots used. Analysis of the nutritive value of the 2 barleys revealed intrinsic differences in the levels of endogenous β-glucanase activity. These differences were extensively evident when the studies were expanded to a range of 64 barley lots. Thus, to clarify the effect of endogenous cellulases on the efficacy of exogenous β-glucanases used to supplement barley-based diets for poultry, 2 barley lots presenting low and high levels of endogenous plant cell wall-degrading enzymes were selected. These lots were used to prepare 2 barley-based diets, which were supplemented with or without a commercial enzyme product and fed to broiler chicks. The data revealed that the exogenous enzymes were effective when the basal diet presented low levels of endogenous β-glucanases but were unable to improve the nutritive value of the barley lot displaying higher β-glucanase activity. Thus, these studies suggest that levels of endogenous β-glucanases may affect the efficacy of exogenous enzymes used to improve the nutritive value of barley-based diets for broilers. The development of a quick β-glucanase assay that could be applied for cereal-based feeds may help identify those barley-based diets that are more responsive to the action of feed enzymes.

Putting an N-terminal end to the Clostridium thermocellum xylanase Xyn10B story: crystal structure of the CBM22-1-GH10 modules complexed with xylohexaose

In general, plant cell wall degrading enzymes are modular proteins containing catalytic domains linked to one or more non-catalytic carbohydrate-binding modules (CBMs). Xyn10B from Clostridium thermocellum is a typical modular enzyme containing an N-terminal family 22 CBM (CBM22-1), a family 10 glycoside hydrolase catalytic domain (GH10), a second CBM22 (CBM22-2), a dockerin sequence and a C-terminal family 1 carbohydrate esterase (CE1) catalytic domain. The structure of the N-terminal bi-modular CBM22-1-GH10 component of Xyn10B has been determined using a SeMet derivative by SAD to 2.5Å. The data was extended to 2.0Å for the non-SeMet mutant complexed with xylohexaose. CBM22-1-GH10 is a 60kDa protein with an E337A mutation to render the GH10 subunit inactive. Three of the six xylose residues of xylohexaose are shown to be bound in the inactivated GH10 substrate binding cleft, with the other three sugars presumably disordered in the solvent channel. The protein is a dimer in the asymmetric unit with extensive surface contacts between the two GH10 modules and between the CBM22-1 and GH10 modules. Residues from helix H4 of the GH10 module provide the major contacts by fitting into the minor groove of the CBM22-1 module. The orientation of CBM22-1 is such that it would allow the substrate to be loosely bound and subsequently delivered to the active site in a processive manner.

Purification, crystallization and crystallographic analysis of Clostridium thermocellum endo-1,4-beta-D-xylanase 10B in complex with xylohexaose

The cellulosome of Clostridium thermocellum is a highly organized multi-enzyme complex of cellulases and hemicellulases involved in the hydrolysis of plant cell-wall polysaccharides. The bifunctional multi-modular xylanase Xyn10B is one of the hemicellulase components of the C. thermocellum cellulosome. The enzyme contains an internal glycoside hydrolase family 10 catalytic domain (GH10) and a C-terminal family 1 carbohydrate esterase domain (CE1). The N-terminal moiety of Xyn10B (residues 32-551), comprising a carbohydrate-binding module (CBM22-1) and the GH10 E337A mutant, was crystallized in complex with xylohexaose. The crystals belong to the trigonal space group P3(2)21 and contain a dimer in the asymmetric unit. The crystals diffracted to beyond 2.0 A resolution.

The Effect of Feeding a Dry Enzyme Mixture with Fibrolytic Activity on the Performance of Lactating Cows and Digestibility of a Diet for Sheep

A dry enzyme mixture was added to the diets of lactating cows and growing lambs to evaluate its ability to improve milk production and nutrient digestibility, respectively. The enzyme mixture contained xylanase and cellulase activity over a broad range of pH (tested from 4 to 7). Twenty-four lactating cows between 50 and 150 d in milk and averaging about 40 kg of milk/ d were fed a total mixed ration (TMR) consisting of 26% [dry matter (DM) basis] corn silage, 17% alfalfa silage, 7% chopped alfalfa hay, and 50% concentrate. One-half of the cows were fed the TMR without supplementation and the remaining half of the cows were fed the same TMR supplemented with 10 g of the enzyme mixture/ cow per day. After 21 d, the treatments were crossed over for a second 21-d period. The dry enzyme mixture had no effect on DM intake, milk production, or milk composition. Addition of various concentrations of the enzyme mixture did not improve the in vitro digestion of neutral detergent fiber from the TMR. In a digestion trial, lambs were fed a commercial diet supplemented with 4 g of the enzyme mixture/lamb per day, and total feces and urine were collected. Although the ratio of enzyme to feed was much higher than it was in the experiment with lactating cows, addition of the enzyme mixture had no effect on the apparent digestion of DM, acid detergent fiber, neutral detergent fiber, or N in the diet.

Mannose foraging by Bacteroides thetaiotaomicron: structure and specificity of the beta-mannosidase, BtMan2A

The human colonic bacterium Bacteroides thetaiotaomicron, which plays an important role in maintaining human health, produces an extensive array of exo-acting glycoside hydrolases (GH), including 32 family GH2 glycoside hydrolases. Although it is likely that these enzymes enable the organism to utilize dietary and host glycans as major nutrient sources, the biochemical properties of these GH2 glycoside hydrolases are currently unclear. Here we report the biochemical properties and crystal structure of the GH2 B. thetaiotaomicron enzyme BtMan2A. Kinetic analysis demonstrates that BtMan2A is a beta-mannosidase in which substrate binding energy is provided principally by the glycone binding site, whereas aglycone recognition is highly plastic. The three-dimensional structure, determined to a resolution of 1.7 A, reveals a five-domain structure that is globally similar to the Escherichia coli LacZ beta-galactosidase. The catalytic center is housed mainly within a (beta/alpha)8 barrel although the N-terminal domain also contributes to the active site topology. The nature of the substrate-binding residues is quite distinct from other GH2 enzymes of known structure, instead they are similar to other clan GH-A enzymes specific for manno-configured substrates. Mutagenesis studies, informed by the crystal structure, identified a WDW motif in the N-terminal domain that makes a significant contribution to catalytic activity. The observation that this motif is invariant in GH2 mannosidases points to a generic role for these residues in this enzyme class. The identification of GH-A clan and GH2 specific residues in the active site of BtMan2A explains why this enzyme is able to harness substrate binding at the proximal glycone binding site more efficiently than mannan-hydrolyzing glycoside hydrolases in related enzyme families. The catalytic properties of BtMan2A are consistent with the flexible nutrient acquisition displayed by the colonic bacterium.

Novel modular enzymes encoded by a cellulase gene cluster in Cellvibrio mixtus

Hydrolysis of plant cell wall polysaccharides, a process which is of intrinsic biological and biotechnological importance, requires the concerted action of an extensive repertoire of microbial cellulases and hemicellulases. Here, we report the identification of the gene cluster unk16A, regA and cel5B in the aerobic soil bacterium Cellvibrio mixtus, encoding a family 16 (CmUnk16A) glycoside hydrolase (GH), an AraC/XylS transcription activator (CmRegA) and a family 5 (CmCel5B) endo-glucanase, respectively. CmUnk16A is a modular enzyme comprising, in addition to the catalytic domain, two family 32 carbohydrate-binding modules (CBMs), termed CBM32-1 and CBM32-2, a CBM4 and a domain of unknown function. We show that CBM32-2 binds weakly to laminarin and pustulan. CmRegA is also a modular protein containing a highly hydrophobic N-terminal domain and a C-terminal DNA-binding domain of the AraC/XylS family. The role of the identified enzymes in the hydrolysis of cell wall polysaccharides by aerobic bacteria is discussed.

Effects of a Proteolytic Feed Enzyme on Intake, Digestion, Ruminal Fermentation, and Milk Production

The effects of exogenous proteolytic enzyme (EPE) on intake, digestibility, ruminal fermentation, and lactational performance were determined using 8 lactating Holstein cows in a double 4 x4 Latin square experiment with a 2 x2 factorial arrangement of treatments. Diets based on barley silage and alfalfa hay as the forage sources were formulated to maintain different forage to concentrate ratios [60:40 vs. 34:66, dry matter (DM) basis]. Four dietary treatments were tested: high forage (HF) without EPE (HF-EPE), HF with EPE (HF+EPE), low forage (LF) without EPE (LF-EPE), and LF with EPE (LF+EPE). The EPE, which contained proteolytic activity but negligible fibrolytic activity, was added to the concentrate portion of the diets after pelleting at a rate of 1.25 mL/kg of DM. Adding EPE to the diet increased total tract digestibilities of DM, organic matter, N, acid detergent fiber, and neutral detergent fiber, with larger increases in digestibility observed for cows fed LF+EPE. Effects of added EPE on in vivo digestibility were consistent with improvements in gas production and degradability of the individual components of the TMR observed in vitro. Ruminal enzymic activities of xylanase and endoglucanase increased with addition of EPE to the diet, which may have accounted for improvements in fiber digestion. However, feeding EPE unexpectedly decreased feed intake of cows, which offset the benefits of improved feed digestibility. Consequently, milk yield of cows fed high or low forage diets decreased with adding EPE. Nevertheless, dairy efficiency, expressed as milk/DM intake, was highest for the LF+EPE diet. Addition of EPE to the diet increased milk fat and milk lactose percentages, but decreased milk protein percentage of cows fed a low forage diet. For cows fed high forage diets, EPE only increased milk lactose percentage. Efficiency of N use for milk production was decreased for both the high and low forage diets when EPE was added to the diet. Mean ruminal pH was lowered when EPE was added a low forage diet, likely due to the increased degradation of forage and concentrate, but there was no effect of EPE on rumen pH when cows were fed high forage diets. Profiles of VFA and microbial yield were not affected by adding EPE to the diets. Adding EPE to a total mixed ration containing alfalfa hay, barley silage, and concentrate improved nutrient digestibility in the total tract, and the response was maximized with a high concentrate diet. However, improvements in digestibility were offset by decreased feed intake, likely due to increased ruminal acidosis.

The Use of Forced Protein Evolution to Investigate and Improve Stability of Family 10 Xylanases

Metal ions such as calcium often play a key role in protein thermostability. The inclusion of metal ions in industrial processes is, however, problematic. Thus, the evolution of enzymes that display enhanced stability, which is not reliant on divalent metals, is an important biotechnological goal. Here we have used forced protein evolution to interrogate whether the stabilizing effect of calcium in an industrially relevant enzyme can be replaced with amino acid substitutions. Our study has focused on the GH10 xylanase CjXyn10A from Cellvibrio japonicus, which contains an extended calcium binding loop that confers proteinase resistance and thermostability. Three rounds of error-prone PCR and selection identified a treble mutant, D262N/A80T/R347C, which in the absence of calcium is more thermostable than wild type CjXyn10A bound to the divalent metal. D262N influences the properties of the calcium binding site, A80T fills a cavity in the enzyme, increasing the number of hydrogen bonds and van der Waals interactions, and the R347C mutation introduces a disulfide bond that decreases the free energy of the unfolded enzyme. A derivative of CjXyn10A (CfCjXyn10A) in which the calcium binding loop has been replaced with a much shorter loop from Cellulomonas fimi CfXyn10A was also subjected to forced protein evolution to select for thermostablizing mutations. Two amino acid substitutions within the introduced loop and the A80T mutation increased the thermostability of the enzyme. This study demonstrates how forced protein evolution can be used to introduce enhanced stability into industrially relevant enzymes while removing calcium as a major stability determinant.

The membrane-bound alpha-glucuronidase from Pseudomonas cellulosa hydrolyzes 4-O-methyl-D-glucuronoxylooligosaccharides but not 4-O-methyl-D-glucuronoxylan

The microbial degradation of xylan is a key biological process. Hardwood 4-O-methyl-D-glucuronoxylans are extensively decorated with 4-O-methyl-D-glucuronic acid, which is cleaved from the polysaccharides by alpha-glucuronidases. In this report we describe the primary structures of the alpha-glucuronidase from Cellvibrio mixtus (C. mixtus GlcA67A) and the alpha-glucuronidase from Pseudomonas cellulosa (P. cellulosa GlcA67A) and characterize P. cellulosa GlcA67A. The primary structures of C. mixtus GlcA67A and P. cellulosa GlcA67A, which are 76% identical, exhibit similarities with alpha-glucuronidases in glycoside hydrolase family 67. The membrane-associated pseudomonad alpha-glucuronidase released 4-O-methyl-D-glucuronic acid from 4-O-methyl-D-glucuronoxylooligosaccharides but not from 4-O-methyl-D-glucuronoxylan. We propose that the role of the glucuronidase, in combination with cell-associated xylanases, is to hydrolyze decorated xylooligosaccharides, generated by extracellular hemicellulases, to xylose and 4-O-methyl-D-glucuronic acid, enabling the pseudomonad to preferentially utilize the sugars derived from these polymers.

The effect of fibrolytic enzymes sprayed onto forages and fed in a total mixed ratio to lactating dairy cows

We investigated the effect of spraying different combinations of fibrolytic enzymes onto forages on their nutritive value for lactating cows. Holstein cows were fed a TMR consisting of 30% corn silage, 15% alfalfa hay, and 55% concentrate (dry matter basis). During a 12-wk treatment period, the forages were treated with no enzymes (control), cellulase D and sultanas B, or cellulase D and xylanase C. Enzymes were diluted in water and sprayed onto the forages while mixing. Both combinations of enzymes supplied similar amounts of fibrolytic activity based on classical enzyme assays conducted at 50 degrees C. Cows fed forages treated with cellulase D and xylanase B tended to produce more 3.5% FCM (+2.5 kg/d) than did cows fed the untreated forages. Dry matter intake, milk production, milk fat, and milk protein were unaffected by treatment. In vitro production of gas from forages treated with enzymes was greater than from untreated forage, but 96-h volatile fatty acid production was not different among treatments. With an alternative enzyme assay based on the depolymerization of dyed substrate at 40 degrees C, activity of xylanase C was greatest at a pH of 6.5 but was substantially reduced as the pH of the assay was decreased. In contrast, xylanase B showed highest activity at pH 5 and enzyme activity was twice that of xylanase B at pH 5.5 and 6. Overall, the results of this study provide more evidence that fibrolytic enzymes can be used to improve milk production in lactating cows.

Transformation and expression of an anaerobic fungal xylanase in several strains of the rumen bacterium Butyrivibrio fibrisolvens

AIMS

To obtain reliable transformation of a range of Butyrivibrio fibrisolvens strains and to express a Neocallimastix patriciarum xylanase gene in the recipients.

METHODS AND RESULTS

Eight strains (H17c, E14, LP1309, LP1028, AR11a, OB156, LP210B and LP461A) of Bu. fibrisolvens were transformed by the Gram-positive vector pUB110. A xylanase expression/secretion cassette containing Bu. fibrisolvens promoter and signal peptide elements fused to catalytic domain II of the N. patriciarum xylanase A cDNA (xynANp) was inserted into pUB110 to create the plasmid pUBxynA. pUBxynA was used to transform seven of the Bu. fibrisolvens strains transformed by pUB110. In strain H17c pUBxynA, which produced native xylanase, 2.46 U mg-1 total xylanase activity was produced with 45% extracellular xylanase. In strain H17c pUMSX, 0.74 U mg-1 total xylanase activity was produced with 98% extracellular xylanase. H17c pUBxynA exhibited increased (28.7%) degradation of neutral detergent fibre compared with unmodified H17c; however, progressive loss of pUBxynA was observed in long-term cultivation.

CONCLUSIONS

A stable transformation system was developed that was applicable for a range of Bu. fibrisolvens strains and high levels of expression of a recombinant xylanase were obtained in H17c which lead to increased fibre digestion.

SIGNIFICANCE AND IMPACT OF THE STUDY

This stable transformation system with the accompanying recombinant plasmids will be a useful tool for further investigation aimed at improving ruminal fibre digestion.

Pseudomonas cellulosa expresses a single membrane-bound glycoside hydrolase family 51 arabinofuranosidase

In the accompanying paper [Beylot, McKie, Voragen, Doeswijk-Voragen and Gilbert (2001) Biochem. J. 358, 607-614] the chromosome of Pseudomonas cellulosa was shown to contain two genes, abf51A and abf62A, that encode arabinofuranosidases belonging to glycoside hydrolase families 51 and 62, respectively. In this report we show that expression of Abf51A is induced by arabinose and arabinose-containing polysaccharides. Northern-blot analysis showed that abf51A was efficiently transcribed, whereas no transcript derived from abf62A was detected in the presence of arabinose-containing polysaccharides. Zymogram and Western-blot analyses revealed that Abf51A was located on the outer membrane of P. cellulosa. To investigate the importance of Abf51A in the release of arabinose from poly- and oligosaccharides, transposon mutagenesis was used to construct an abf51A-inactive mutant of P. cellulosa (Deltaabf51A). The mutant did not grow on linear arabinan or sugar beet arabinan, and utilized arabinoxylan much more slowly than the wild-type bacterium. Arabinofuranosidase activity in Deltaabf51A against aryl-alpha-arabinofuranosides, arabinan and alpha1,5-linked arabino-oligosaccharides was approx. 1% of the wild-type bacterium. The mutant bacterium did not exhibit arabinofuranosidase activity against arabinoxylan, supporting the view that abf62A is not expressed in P. cellulosa. These data indicate that P. cellulosa expresses a membrane-bound glycoside hydrolase family 51 arabinofuranosidase that plays a pivotal role in releasing arabinose from polysaccharides and arabino-oligosaccharides.

Expression of Bacillus circulans Teri-42 xylanase gene in Bacillus subtilis

The xylanase gene of Bacillus circulans Teri-42 was cloned in both B. subtilis and Escherichia coli. The enzyme activity was almost 87% higher in B. subtilis (pBA7) than in E. coli (pAQ4). No cellulase activity was detected in the clones, B. subtilis (pBA7) and E. coli (pAQ4). Approximately 1120 U (80%) of the xylanase was secreted extracellularly by the clone B. subtilis (pBA7) as compared to 79 U (88%) excreted in E. coli (pAQ4). In B. subtilis (pBA7) the optimal xylanase activity was at pH 7.0 and 50 degrees C, which was the same as that of the parent B. circulans Teri-42. The recombinant xylanase in B. subtilis was more stable at higher temperatures than the parent B. circulans Teri-42. Purification of xylanase from the clone B. subtilis (pBA7) showed a 71 kDa polypeptide similar to that observed in B. circulans Teri-42.

Structural, kinetic, and calorimetric characterization of the cold-active phosphoglycerate kinase from the antarctic Pseudomonas sp. TACII18

The gene encoding the phosphoglycerate kinase (PGK) from the Antarctic Pseudomonas sp. TACII18 has been cloned and found to be inserted between the genes encoding for glyceraldhyde-3-phosphate dehydrogenase and fructose aldolase. The His-tagged and the native recombinant PGK from the psychrophilic Pseudomonas were expressed in Escherichia coli. The wild-type and the native recombinant enzymes displayed identical properties, such as a decreased thermostability and a 2-fold higher catalytic efficiency at 25 degrees C when compared with the mesophilic PGK from yeast. These properties, which reflect typical features of cold-adapted enzymes, were strongly altered in the His-tagged recombinant PGK. The structural model of the psychrophilic PGK indicated that a key determinant of its low stability is the reduced number of salt bridges, surface charges, and aromatic interactions when compared with mesophilic and thermophilic PGK. Differential scanning calorimetry of the psychrophilic PGK revealed unusual variations in its conformational stability for the free and substrate-bound forms. In the free form, a heat-labile and a thermostable domain unfold independently. It is proposed that the heat-labile domain acts as a destabilizing domain, providing the required flexibility around the active site for catalysis at low temperatures.

Stability and stabilization of potential feed additive enzymes in rumen fluid*

Four commercial preparations of fibrolytic enzymes, from Irpex lacteus, Trichoderma viride, Aspergillus niger, and a mixture designed to be similar to the I. lacteus extract, were incubated in vitro with digesta taken from the rumen of sheep receiving a grass hay/concentrate diet, and the survival of major enzyme activities was measured. Some activities, including the beta-1,4-endoglucanase and xylanase from the extract derived from Aspergillus niger, were stable for at least 6 h in rumen fluid. The same activities in the other extracts also retained substantial activity for several hours. beta-Glucosidase and beta-xylosidase activities were much more labile, most being almost completely destroyed after 1 h, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that most proteins in the extracts were digested extensively after up to 7 h of incubation. Adding bovine serum albumin (0.5 g/l) to the incubation increased the half-life of Trichoderma viride beta-glucosidase activity from less than 0.5 h to 3 h. Proteins extracted from plant materials, particularly the soybean 7S globulin fraction, also conferred protection from proteolytic breakdown, but none was as effective as bovine serum albumin. It was concluded that the stability of most fibrolytic enzymes in rumen fluid is not likely to be a limiting factor in the use of enzymes as feed additives for ruminants; but if the enzymes are not stable, means can be found for their stabilization.

The effect of treating forages with fibrolytic enzymes on its nutritive value and lactation performance of dairy cows

Forages (corn silage and alfalfa hay) were sprayed with liquid enzymes prior to combining with a concentrate to form a total mixed ration (50% forage:50% concentrate, dry matter basis) and fed to lactating cows. In the first year, treatments were 1) no enzymes, 2) an enzyme complex containing 3500 carboxymethyl cellulase (CMCase) and 16,000 xylanase units per kilogram of forage dry matter, or 3) an enzyme complex containing 8800 CMCase units and 40,000 xylanase units. In the second year, the treatments were 1) no enzymes, 2) an enzyme complex as in yr 1 containing 3700 CMCase and 14,000 xylanase units, or 3) an enzyme complex using an alternative cellulase and containing 3600 CMCase and 11,000 xylanase units. In the first year, cows fed diet 2 tended to produce more milk (39.5 kg/d) than those fed diet 1 (37.0 kg/d) or those fed diet 3 (36.2 kg/d). The high level of enzyme treatment in diet 3 decreased the output of milk protein and fat compared to the low level of enzyme treatment. In the second year, cows fed diet 3 produced more milk (35.4 kg/d) than did those fed diet 1 (32.9 kg/d) and numerically more than those fed diet 2 (33.6 kg/d). Milk fat and protein were similar among treatments but numerically lower for cows fed enzyme-treated forages. Dry matter intake (kg/d) was similar among treatments in both years. Spraying certain doses and combinations of enzymes directly onto forages prior to feeding can improve milk yields but enzyme sources and dose levels are of critical importance.

Bacterial xylanase expression in mammalian cells and transgenic mice

The energy which simple-stomached livestock can derive from dietary plant material is limited by the lack of plant polysaccharide degrading enzymes in their gastro-intestinal (GI) tract and the inefficient microbial fermentation of such material in their hind-gut. In poultry the non-starch polysaccharides found in cereal grains can also impair normal digestive function as they form viscous gels in the GI tract inhibiting the breakdown and absorption of nutrients. The nutrition of such livestock could, therefore, be improved by the introduction of enzymes able to degrade plant polysaccharides in the small intestine. We describe the expression of a xylanase, XYLY', from the bacterium Clostridium thermocellum in mammalian cells and the exocrine pancreas of transgenic mice. The enzyme is synthesised, secreted and functionally active in the eukaryote system. This work demonstrates the feasibility of generating animals with the endogenous capacity to depolymerise the xylan component of hemi-cellulose.

Effects of an enzyme feed additive on extent of digestion and milk production of lactating dairy cows

A study was conducted using lactating Holstein cows with ruminal and duodenal cannulas in a 4 x 4 Latin square design to investigate fibrolytic enzyme supplementation on site and extent of nutrient digestion. The four diets consisted of 45% concentrate, 10% barley silage, and 45% cubed alfalfa hay (dry matter basis) and differed in enzyme supplementation: 1) control cubes, 2) cubes treated with 1 g of enzyme mixture/kg of cubes, 3) cubes treated with 2 g of enzyme mixture/kg of cubes, and 4) both concentrate and cubes treated with 1 g of enzyme mixture/kg of dry matter. The enzyme supplement contained primarily cellulase and xylanase activities. Digestion of organic matter and neutral detergent fiber in the total tract was higher for cows fed the high dosage of enzyme than for cows fed the control cubes. Ruminal digestibility of crude protein was higher, but that of organic matter and neutral detergent fiber was only numerically higher, for cows fed the high dosage of enzyme compared with that of cows fed the control cubes. Higher ruminal digestibility associated with the high dosage of enzyme resulted in more microbial protein synthesis. Milk production increased for cows fed the high dosage of enzyme compared with cows fed the control cubes and effects of the addition of enzyme on milk composition were minimal. The results demonstrated the benefits of using a fibrolytic enzyme additive to enhance feed digestion and milk production by dairy cows. The response to enzyme supplementation was affected more by amount of enzyme than by whether the enzyme was added to forage or concentrate.

Calcium protects a mesophilic xylanase from proteinase inactivation and thermal unfolding

Crystal structure analysis of Pseudomonas fluorescens subsp. cellulosa xylanase A (XYLA) indicated that the enzyme contained a single calcium binding site that did not exhibit structural features typical of the EF-hand motif. Isothermal titration calorimetry revealed that XYLA binds calcium with a Ka of 4.9 x 10(4) M-1 and a stoichiometry consistent with one calcium binding site per molecule of enzyme. Occupancy of the calcium binding domain with its ligand protected XYLA from proteinase and thermal inactivation and increased the melting temperature of the enzyme from 60.8 to 66.5 degrees C. However, the addition of calcium or EDTA did not influence the catalytic activity of the xylanase. Replacement of the calcium binding domain, which is located within loop 7 of XYLA, with the corresponding short loop from Cex (a Cellulomonas fimi xylanase/exoglucanase), did not significantly alter the biochemical properties of the enzyme. These data suggest that the primary function of the calcium binding domain is to increase the stability of the enzyme against thermal unfolding and proteolytic attack. To understand further the nature of the calcium binding domain of XYLA, four variants of the xylanase, D256A, N261A, D262A, and XYLA"', in which Asp-256, Asn-261, and Asp-262 had all been changed to alanine, were constructed. These mutated enzymes did not show any significant binding to Ca2+, indicating that Asp-256, Asn-261, and Asp-262 play a pivotal role in the affinity of XYLA for the divalent cation. In the presence or absence of calcium, XYLA"' exhibited thermal stability similar to that of the native enzyme bound to Ca2+ ions, although the variant was sensitive to proteinase inactivation. The role of the calcium binding domain in vivo and the possible mechanism by which the domain evolved are discussed.

A modular xylanase from mesophilic Cellulomonas fimi contains the same cellulose-binding and thermostabilizing domains as xylanases from thermophilic bacteria

The xynC gene from mesophilic Cellulomonas fimi encodes a large 125 kDa modular xylanase (XYLC), consisting of six distinct functional domains. In addition to a single Family 10 catalytic domain, XYLC contains a domain homologous with the nodulation protein, NodB, from nitrogen-fixing bacteria and thermostabilizing and cellulose-binding domains found previously only in xylanases from thermophilic bacteria.

Purification and characterization of two different xylanases from the thermophilic actinomycete Microtetraspora flexuosa SIIX

Two endoxylanases were isolated from the xylanolytic enzyme system of the thermophilic actinomycete Microtetraspora flexuosa SIIX, and purified by ammonium sulfate fractionation, DEAE-Sepharose chromatography, gel filtration on Sephacryl S 200 and fast protein liquid chromatography on Q-Sepharose. The molecular masses of xylanase I and II were 26.3 and 16.8 kDa, and isoelectric points were 8.4 and 9.45, respectively. Optimal enzyme activities were obtained at 80 degrees C and pH 6.0. The thermostability of both xylanases was greatly diminished during purification but could be restored by preincubation of the purified enzymes in the presence of xylan. The half-lives at 80 degrees C were approximately 25 min. The kinetic constants of xylanases I and II determined with Remazol-brilliant-blue xylan were Vmax of 1537 and 353 mumol.min-1.mg protein-1 and K(m) values of 2.44 and 1.07 mg.ml-1, respectively. Purified xylanases utilized xylan as well as small oligosaccharides such as xylotriose as substrate. They did not exhibit xylobiase or debranching activities. The predominant products of arabinoxylan hydrolysis were xylobiose and xylotriose, the latter being hydrolysed to xylobiose and xylose upon further incubation. In addition, fragments containing arabinose side chains accumulated. The xylanases did not act on crystalline or amorphous cellulose indicating a possible application in biobleaching processes.

The conserved noncatalytic 40-residue sequence in cellulases and hemicellulases from anaerobic fungi functions as a protein docking domain

Two cDNAs, designated xynA and manA, encoding xylanase A (XYLA) and mannanase A (MANA), respectively, were isolated from a cDNA library derived from mRNA extracted from the anaerobic fungus, Piromyces. XYLA and MANA displayed properties typical of endo-beta 1,4-xylanases and mannanases, respectively. Neither enzyme hydrolyzed cellulosic substrates. The nucleotide sequences of xynA and manA revealed open reading frames of 1875 and 1818 base pairs, respectively, coding for proteins of M(r) 68,049 (XYLA) and 68,055 (MANA). The deduced primary structure of MANA revealed a 458-amino acid sequence that exhibited identity with Bacillus and Pseudomonas fluorescens subsp. cellulosa mannanases belonging to glycosyl hydrolase Family 26. A 40-residue reiterated sequence, which was homologous to duplicated noncatalytic domains previously observed in Neocallimastix patriciarum xylanase A and endoglucanase B, was located at the C terminus of MANA. XYLA contained two regions that exhibited sequence identity with the catalytic domains of glycosyl hydrolase Family 11 xylanases and were separated by a duplicated 40-residue sequence that exhibited strong homology to the C terminus of MANA. Analysis of truncated derivatives of MANA confirmed that the N-terminal 458-residue sequence constituted the catalytic domain, while the C-terminal domain was not essential for the retention of catalytic activity. Similar deletion analysis of XYLA showed that the C-terminal catalytic domain homologue exhibited catalytic activity, but the corresponding putative N-terminal catalytic domain did not function as a xylanase. Fusion of the reiterated noncatalytic 40-residue sequence conserved in XYLA and MANA to glutathione S-transferase, generated a hybrid protein that did not associate with cellulose, but bound to 97- and 116-kDa polypeptides that are components of the multienzyme cellulase-hemicellulase complexes of Piromyces and Neocallimastix patriciarum, respectively. The role of this domain in the assembly of the enzyme complex is discussed.

The non-catalytic cellulose-binding domain of a novel cellulase from Pseudomonas fluorescens subsp. cellulosa is important for the efficient hydrolysis of Avicel

A genomic library of Pseudomonas fluorescens subsp. cellulosa DNA, constructed in lambda ZAPII, was screened for carboxymethyl-cellulase activity. The pseudomonad insert from a recombinant phage which displayed elevated cellulase activity in comparison with other cellulase-positive clones present in the library, was excised into pBluescript SK- to generate the plasmid pC48. The nucleotide sequence of the cellulase gene, designated celE, revealed a single open reading frame of 1710 bp that encoded a polypeptide, defined as endoglucanase E (CelE), of M(r) 59663. The deduced primary structure of CelE revealed an N-terminal signal peptide followed by a 300-amino-acid sequence that exhibited significant identity with the catalytic domains of cellulases belonging to glycosyl hydrolase Family 5. Adjacent to the catalytic domain was a 40-residue region that exhibited strong sequence identity to non-catalytic domains located in two other endoglucanases and a xylanase from P. fluorescens. The C-terminal 100 residues of CelE were similar to Type-I cellulose-binding domains (CBDs). The three domains of the cellulase were joined by linker sequences rich in serine residues. Analysis of the biochemical properties of full-length and truncated derivatives of CelE confirmed that the enzyme comprised an N-terminal catalytic domain and a C-terminal CBD. Analysis of purified CelE revealed that the enzyme had an M(r) of 56000 and an experimentally determined N-terminal sequence identical to residues 40-54 of the deduced primary structure of full-length CelE. The enzyme exhibited an endo mode of action in hydrolysing a range of cellulosic substrates including Avicel and acid-swollen cellulose, but did not attack xylan or any other hemicelluloses. A truncated form of the enzyme, which lacked the C-terminal CBD, displayed the same activity as full-length CelE against soluble cellulose and acid-swollen cellulose, but exhibited substantially lower activity than the full-length cellulase against Avicel. The significance of these data in relation to the role of the CBD is discussed.