Characterization of a thermostable family 10 endo-xylanase (XynB) from Thermotoga maritima that cleaves p-nitrophenyl-β-d-xyloside

Identification of a novel glycoside hydrolase family 8 xylanase from Deinococcus geothermalis and its application at low temperatures

Xylanase is the most important hydrolase in the xylan hydrolase system, the main function of which is β-1,4-endo-xylanase, which randomly cleaves xylans to xylo-oligosaccharides and xylose. Xylanase has wide ranging of applications, but there remains little research on the cold-adapted enzymes required in some low-temperature industries. Glycoside hydrolase family 8 (GH8) xylanases have been reported to have cold-adapted enzyme activity. In this study, the xylanase gene dgeoxyn was excavated from Deinococcus geothermalis through sequence alignment. The recombinant xylanase DgeoXyn encodes 403 amino acids with a theoretical molecular weight of 45.39 kDa. Structural analysis showed that DgeoXyn has a (α/α)6-barrel fold structure typical of GH8 xylanase. At the same time, it has strict substrate specificity, is only active against xylan, and its hydrolysis products include xylobiose, xylotrinose, xytetranose, xylenanose, and a small amount of xylose. DgeoXyn is most active at 70 ℃ and pH 6.0. It is very stable at 10, 20, and 30 ℃, retaining more than 80% of its maximum enzyme activity. The enzyme activity of DgeoXyn increased by 10% after the addition of Mn2+ and decreased by 80% after the addition of Cu2+. The Km and Vmax of dgeox were 42 mg/ml and 20,000 U/mg, respectively, at a temperature of 70 ℃ and pH of 6.0 using 10 mg/ml beechwood xylan as the substrate. This research on DgeoXyn will provide a theoretical basis for the development and application of low-temperature xylanase.

Recalcitrant cell wall of Ulva lactuca seaweed is degraded by a single ulvan lyase from family 25 of polysaccharide lyases

Green macroalgae, e.g., Ulva lactuca, are valuable bioactive sources of nutrients; but algae recalcitrant cell walls, composed of a complex cross-linked matrix of polysaccharides, can compromise their utilization as feedstuffs for monogastric animals. This study aimed to evaluate the ability of pre-selected Carbohydrate-Active enZymes (CAZymes) and sulfatases to degrade U. lactuca cell walls and release nutritive compounds. A databank of 199 recombinant CAZymes and sulfatases was tested in vitro for their action towards U. lactuca cell wall polysaccharides. The enzymes were incubated with the macroalga, either alone or in combination, to release reducing sugars and decrease fluorescence intensity of Calcofluor White stained cell walls. The individual action of a polysaccharide lyase family 25 (PL25), an ulvan lyase, was shown to be the most efficient in cell wall disruption. The ulvan lyase treatment, in triplicate measures, promoted the release of 4.54 g/L (P < 0.001) reducing sugars, a mono- and oligosaccharides release of 11.4 and 11.2 mmol/100 g of dried alga (P < 0.01), respectively, and a decrease of 41.7% (P < 0.001) in cell wall fluorescence, in comparison to control. The ability of ulvan lyase treatment to promote the release of nutritional compounds from alga biomass was also evaluated. A release of some monounsaturated fatty acids was observed, particularly the health beneficial 18:1c9 (P < 0.001). However, no significant release of total fatty acids (P > 0.05), proteins (P = 0.861) or pigments (P > 0.05) was found. These results highlight the capacity of a single recombinant ulvan lyase (PL25 family) to incompletely disrupt U. lactuca cell walls. This enzyme could enhance the bioaccessibility of U. lactuca bioactive products with promising utilization in the feed industry.

A novel acid-tolerant β-xylanase from Scytalidium candidum 3C for the synthesis of o-nitrophenyl xylooligosaccharides

Endo-β-xylanases are hemicellulases involved in the conversion of xylans in plant biomass. Here, we report a novel acidophilic β-xylanase (ScXynA) with high transglycosylation abilities that was isolated from the filamentous fungus Scytalidium candidum 3C. ScXynA was identified as a glycoside hydrolase family 10 (GH10) dimeric protein, with a molecular weight of 38 ± 5 kDa per subunit. The enzyme catalyzed the hydrolysis of different xylans under acidic conditions and was stable in the pH range 2.6-4.5. The kinetic parameters of ScXynA were determined in hydrolysis reactions with p-nitrophenyl-β-d-cellobioside (pNP-β-Cel) and p-nitrophenyl-β-d-xylobioside (pNP-β-Xyl₂ ), and k_cat /K_m was found to be 0.43 ± 0.02 (s·mM)^-1 and 57 ± 3 (s·mM)^-1 , respectively. In the catalysis of the transglycosylation o-nitrophenyl-β-d-xylobioside (oNP-β-Xyl₂ ) acted both as a donor and an acceptor, resulting in the efficient production of o-nitrophenyl xylooligosaccharides, with a degree of polymerization of 3-10 and o-nitrophenyl-β-d-xylotetraose (oNP-β-Xyl₄ ) as the major product (18.5% yield). The modeled ScXynA structure showed a favorable position for ligand entry and o-nitrophenyl group accommodation in the relatively open -3 subsite, while the cleavage site was covered with an extended loop. These structural features provide favorable conditions for transglycosylation with oNP-β-Xyl₂ . The acidophilic properties and high transglycosylation activity make ScXynA a suitable choice for various biotechnological applications, including the synthesis of valuable xylooligosaccharides.

Improving the catalytic activity of thermostable xylanase from Thermotoga maritima via mutagenesis of non-catalytic residues at glycone subsites

Endo-β-1,4-xylanase from Thermotoga maritima, TmxB, is an industrially attractive enzyme due to its extreme thermostability. To improve its application value, four variants were designed on the basis of multiple sequence and three-dimensional structure alignments. Wild-type TmxB (wt-TmxB) and its mutants were produced via a Pichia pastoris expression system. Among four single-site mutants, the tyrosine substitution of a threonine residue (T74Y) at putative -3/-4 subsite led to a 1.3-fold increase in specific activity at 40 °C - 100 °C and pH 5 for 5 min, with beechwood xylan as the substrate. T74Y had an improved catalytic efficiency (k_cat/K_m), being 1.6 times that of wt-TmxB. Variants DY (two amino acid insertions) and N68Q displayed a slight increase (1.2 fold) and dramatic decline (1.7 fold) in catalytic efficiency, respectively. Mutant E67Y was totally inactive under all test conditions. Structural modeling and docking simulation elucidated structural insights into the molecular mechanism of activity changes for these TmxB variants. This study helps in further understanding the roles of the non-catalytic amino acids at the glycone subsites of xylanases from glycoside hydrolase family 10.

A thermophilic and thermostable xylanase from Caldicoprobacter algeriensis: Recombinant expression, characterization and application in paper biobleaching

A novel xylanase gene xynBCA, encoding a polypeptide of 439 residues (XynBCA), was cloned from Caldicoprobacter algeriensis genome and recombinantly expressed in Escherichia coli BL21(DE3). The amino acid sequence analysis showed that XynBCA belongs to the glycoside hydrolase family 10. The purified recombinant enzyme has a monomeric structure of 52 kDa. It is active and stable in a wide range of pH from 3 to 10 with a maximum activity at 6.5. Interestingly, XynBCA was highly thermoactive with an optimum temperature of 80 °C, thermostable with a half-life of 20 min at 80 °C. The specific activity was 117 U mg^-1, while the K_m and V_max were 1.247 mg ml^-1, and 114.7 μmol min^-1 mg^-1, respectively. The investigation of XynBCA in kraft pulp biobleaching experiments showed effectiveness in releasing reducing sugars and chromophores, with best achievements at 100 U g^-1 of pulp and 1 h of incubation. The comparative molecular modeling studies with the less thermostable Xylanase B from Clostridium stercorarium, revealed extra charged residues at the surface of XynBCA potentially participating in the formation of intermolecular hydrogen bonds with solvent molecules or generating salt bridges, therefore contributing to the higher thermal stability.

Structural and functional characterization of a bifunctional GH30-7 xylanase B from the filamentous fungus Talaromyces cellulolyticus

Glucuronoxylanases are endo-xylanases and members of the glycoside hydrolase family 30 subfamilies 7 (GH30-7) and 8 (GH30-8). Unlike for the well-studied GH30-8 enzymes, the structural and functional characteristics of GH30-7 enzymes remain poorly understood. Here, we report the catalytic properties and three-dimensional structure of GH30-7 xylanase B (Xyn30B) identified from the cellulolytic fungus Talaromyces cellulolyticus Xyn30B efficiently degraded glucuronoxylan to acidic xylooligosaccharides (XOSs), including an α-1,2-linked 4-O-methyl-d-glucuronosyl substituent (MeGlcA). Rapid analysis with negative-mode electrospray-ionization multistage MS (ESI(-)-MS ⁿ ) revealed that the structures of the acidic XOS products are the same as those of the hydrolysates (MeGlcA²Xyl _n , n > 2) obtained with typical glucuronoxylanases. Acidic XOS products were further degraded by Xyn30B, releasing first xylobiose and then xylotetraose and xylohexaose as transglycosylation products. This hydrolase reaction was unique to Xyn30B, and the substrate was cleaved at the xylobiose unit from its nonreducing end, indicating that Xyn30B is a bifunctional enzyme possessing both endo-glucuronoxylanase and exo-xylobiohydrolase activities. The crystal structure of Xyn30B was determined as the first structure of a GH30-7 xylanase at 2.25 Å resolution, revealing that Xyn30B is composed of a pseudo-(α/β)₈-catalytic domain, lacking an α6 helix, and a small β-rich domain. This structure and site-directed mutagenesis clarified that Arg⁴⁶, conserved in GH30-7 glucuronoxylanases, is a critical residue for MeGlcA appendage-dependent xylan degradation. The structural comparison between Xyn30B and the GH30-8 enzymes suggests that Asn⁹³ in the β2-α2 loop is involved in xylobiohydrolase activity. In summary, our findings indicate that Xyn30B is a bifunctional endo- and exo-xylanase.

Understanding the Positional Binding and Substrate Interaction of a Highly Thermostable GH10 Xylanase from Thermotoga maritima by Molecular Docking

Glycoside hydrolase family 10 (GH10) xylanases are responsible for enzymatic cleavage of the internal glycosidic linkages of the xylan backbone, to generate xylooligosaccharides (XOS) and xyloses. The topologies of active-site cleft determine the substrate preferences and product profiles of xylanases. In this study, positional bindings and substrate interactions of TmxB, one of the most thermostable xylanases characterized from Thermotoga maritima to date, was investigated by docking simulations. XOS with backbone lengths of two to five (X2–X5) were docked into the active-site cleft of TmxB by AutoDock The modeled complex structures provided a series of snapshots of the interactions between XOS and TmxB. Changes in binding energy with the length of the XOS backbone indicated the existence of four effective subsites in TmxB. The interaction patterns at subsites −2 to +1 in TmxB were conserved among GH10 xylanases whereas those at distal aglycone subsite +2, consisting of the hydrogen bond network, was unique for TmxB. This work helps in obtaining an in-depth understanding of the substrate-binding property of TmxB and provides a basis for rational design of mutants with desired product profiles.

Characterization of Two Endo-β-1, 4-Xylanases from Myceliophthora thermophila and Their Saccharification Efficiencies, Synergistic with Commercial Cellulase

The xylanases with high specific activity and resistance to harsh conditions are of high practical value for biomass utilization. In the present study, two new GH11 xylanase genes, MYCTH_56237 and MYCTH_49824, have been cloned from thermophilic fungus Myceliophthora thermophila and expressed in Pichia pastoris. The specific activities of purified xylanases reach approximately 1,533.7 and 1,412.5 U/mg, respectively. Based on multiple template-based homology modeling, the structures of their catalytic domains are predicted. Enzyme activity was more effective in 7.5 L fermentor, yielding 2,010.4 and 2,004.2 U/mL, respectively. Both enzymes exhibit optimal activity at 60°C with pH of 6.0 and 7.0, respectively. Their activities are not affected by EDTA and an array of metal ions. The kinetic constants have been determined for MYCTH_56237 (K_m = 8.80 mg/mL, V_max = 2,380 U/mg) and MYCTH_49824 (K_m = 5.67 mg/mL, V_max = 1,750 U/mg). More importantly, both xylanases significantly cooperate with the commercial cellulase Celluclast 1.5 L in terms of the saccharification efficiency. All these biochemical properties of the xylanases offer practical potential for future applications.

Enhancement of cellulosome-mediated deconstruction of cellulose by improving enzyme thermostability

BACKGROUND

The concerted action of three complementary cellulases from Clostridium thermocellum, engineered to be stable at elevated temperatures, was examined on a cellulosic substrate and compared to that of the wild-type enzymes. Exoglucanase Cel48S and endoglucanase Cel8A, both key elements of the natural cellulosome from this bacterium, were engineered previously for increased thermostability, either by SCHEMA, a structure-guided, site-directed protein recombination method, or by consensus-guided mutagenesis combined with random mutagenesis using error-prone PCR, respectively. A thermostable β-glucosidase BglA mutant was also selected from a library generated by error-prone PCR that will assist the two cellulases in their methodic deconstruction of crystalline cellulose. The effects of a thermostable scaffoldin versus those of a largely mesophilic scaffoldin were also examined. By improving the stability of the enzyme subunits and the structural component, we aimed to improve cellulosome-mediated deconstruction of cellulosic substrates.

RESULTS

The results demonstrate that the combination of thermostable enzymes as free enzymes and a thermostable scaffoldin was more active on the cellulosic substrate than the wild-type enzymes. Significantly, "thermostable" designer cellulosomes exhibited a 1.7-fold enhancement in cellulose degradation compared to the action of conventional designer cellulosomes that contain the respective wild-type enzymes. For designer cellulosome formats, the use of the thermostabilized scaffoldin proved critical for enhanced enzymatic performance under conditions of high temperatures.

CONCLUSIONS

Simple improvement in the activity of a given enzyme does not guarantee its suitability for use in an enzyme cocktail or as a designer cellulosome component. The true merit of improvement resides in its ultimate contribution to synergistic action, which can only be determined experimentally. The relevance of the mutated thermostable enzymes employed in this study as components in multienzyme systems has thus been confirmed using designer cellulosome technology. Enzyme integration via a thermostable scaffoldin is critical to the ultimate stability of the complex at higher temperatures. Engineering of thermostable cellulases and additional lignocellulosic enzymes may prove a determinant parameter for development of state-of-the-art designer cellulosomes for their employment in the conversion of cellulosic biomass to soluble sugars.Graphical abstractConversion of conventional designer cellulosomes into thermophilic designer cellulosomes.

Improved lignocellulose conversion to biofuels with thermophilic bacteria and thermostable enzymes

Second-generation feedstock, especially nonfood lignocellulosic biomass is a potential source for biofuel production. Cost-intensive physical, chemical, biological pretreatment operations and slow enzymatic hydrolysis make the overall process of lignocellulosic conversion into biofuels less economical than available fossil fuels. Lignocellulose conversions carried out at ≤ 50 °C have several limitations. Therefore, this review focuses on the importance of thermophilic bacteria and thermostable enzymes to overcome the limitations of existing lignocellulosic biomass conversion processes. The influence of high temperatures on various existing lignocellulose conversion processes and those that are under development, including separate hydrolysis and fermentation, simultaneous saccharification and fermentation, and extremophilic consolidated bioprocess are also discussed.

Functional and structural characterization of a thermostable acetyl esterase from Thermotoga maritima

TM0077 from Thermotoga maritima is a member of the carbohydrate esterase family 7 and is active on a variety of acetylated compounds, including cephalosporin C. TM0077 esterase activity is confined to short-chain acyl esters (C2-C3), and is optimal around 100°C and pH 7.5. The positional specificity of TM0077 was investigated using 4-nitrophenyl-β-D-xylopyranoside monoacetates as substrates in a β-xylosidase-coupled assay. TM0077 hydrolyzes acetate at positions 2, 3, and 4 with equal efficiency. No activity was detected on xylan or acetylated xylan, which implies that TM0077 is an acetyl esterase and not an acetyl xylan esterase as currently annotated. Selenomethionine-substituted and native structures of TM0077 were determined at 2.1 and 2.5 Å resolution, respectively, revealing a classic α/β-hydrolase fold. TM0077 assembles into a doughnut-shaped hexamer with small tunnels on either side leading to an inner cavity, which contains the six catalytic centers. Structures of TM0077 with covalently bound phenylmethylsulfonyl fluoride and paraoxon were determined to 2.4 and 2.1 Å, respectively, and confirmed that both inhibitors bind covalently to the catalytic serine (Ser188). Upon binding of inhibitor, the catalytic serine adopts an altered conformation, as observed in other esterase and lipases, and supports a previously proposed catalytic mechanism in which Ser hydroxyl rotation prevents reversal of the reaction and allows access of a water molecule for completion of the reaction.

Thermal-induced conformational changes in the product release area drive the enzymatic activity of xylanases 10B: Crystal structure, conformational stability and functional characterization of the xylanase 10B from Thermotoga petrophila RKU-1

Endo-xylanases play a key role in the depolymerization of xylan and recently, they have attracted much attention owing to their potential applications on biofuels and paper industries. In this work, we have investigated the molecular basis for the action mode of xylanases 10B at high temperatures using biochemical, biophysical and crystallographic methods. The crystal structure of xylanase 10B from hyperthermophilic bacterium Thermotoga petrophila RKU-1 (TpXyl10B) has been solved in the native state and in complex with xylobiose. The complex crystal structure showed a classical binding mode shared among other xylanases, which encompasses the -1 and -2 subsites. Interestingly, TpXyl10B displayed a temperature-dependent action mode producing xylobiose and xylotriose at 20°C, and exclusively xylobiose at 90°C as assessed by capillary zone electrophoresis. Moreover, circular dichroism spectroscopy suggested a coupling effect of temperature-induced structural changes with this particular enzymatic behavior. Molecular dynamics simulations supported the CD analysis suggesting that an open conformational state adopted by the catalytic loop (Trp297-Lys326) provokes significant modifications in the product release area (+1,+2 and +3 subsites), which drives the enzymatic activity to the specific release of xylobiose at high temperatures.

Xyn10A, a thermostable endoxylanase from Acidothermus cellulolyticus 11B

We cloned and purified the major family 10 xylanase (Xyn10A) from Acidothermus cellulolyticus 11B. Xyn10A was active on oat spelt and birchwood xylans between 60°C and 100°C and between pH 4 and pH 8. The optimal activity was at 90°C and pH 6; specific activity and K(m) for oat spelt xylan were 350 μmol xylose produced min⁻¹ mg of protein⁻¹ and 0.53 mg ml⁻¹, respectively. Based on xylan cleavage patterns, Xyn10A is an endoxylanase, and its half-life at 90°C was approximately 1.5 h in the presence of xylan.

Thermostable enzymes as biocatalysts in the biofuel industry

Lignocellulose is the most abundant carbohydrate source in nature and represents an ideal renewable energy source. Thermostable enzymes that hydrolyze lignocellulose to its component sugars have significant advantages for improving the conversion rate of biomass over their mesophilic counterparts. We review here the recent literature on the development and use of thermostable enzymes for the depolymerization of lignocellulosic feedstocks for biofuel production. Furthermore, we discuss the protein structure, mechanisms of thermostability, and specific strategies that can be used to improve the thermal stability of lignocellulosic biocatalysts.

Molecular and biochemical characterization of a novel xylanase from the symbiotic Sphingobacterium sp. TN19

A xylanase-encoding gene, designated xynA19, was cloned from Sphingobacterium sp. TN19--a symbiotic bacterium isolated from the gut of Batocera horsfieldi larvae--and expressed in Escherichia coli BL21 (DE3). The full-length xynA19 (1,155 bp in length) encodes a 384-residue polypeptide (XynA19) containing a predicted signal peptide of 24 residues and a catalytic domain belonging to glycosyl hydrolase family 10 (GH 10). The deduced amino acid sequence of XynA19 is most similar (53.1% identity) to an endo-1,4-beta-xylanase from Prevotella bryantii B(1)4. Phylogenetic analysis of GH 10 Bacteroidia xylanases indicated that GH 10 xylanases from Sphingobacteria were separated into two clusters, and XynA19 is more closely related to the xylanases of Bacteroidia from gut or rumen than to those of Flavobacteria and Sphingobacteria from other sources. Recombinant XynA19 (r-XynA19) showed apparent optimal activity at pH 6.5 and 45 degrees C. Compared with thermophilic and mesophilic counterparts, r-XynA19 was more active at low temperatures, retaining >65% of its maximum activity at 20-28 degrees C and approximately 40% even at 10 degrees C, and modeling indicated that XynA19 has fewer hydrogen bonds and salt bridges. These properties suggest that XynA19 has various potential applications, especially in aquaculture and the food industry.

Engineering the thermostability of a TIM-barrel enzyme by rational family shuffling

A possible approach to generate enzymes with an engineered temperature optimum is to create chimeras of homologous enzymes with different temperature optima. We tested this approach using two family-10 xylanases from Thermotoga maritima: the thermophilic xylanase A catalytic domain (TmxAcat, T(opt)=68 degrees C), and the hyperthermophilic xylanase B (TmxB, T(opt)=102 degrees C). Twenty-one different chimeric constructs were created by mimicking family shuffling in a rational manner. The measured temperature optima of the 16 enzymatically active chimeras do not monotonically increase with the percentage of residues coming from TmxB. Only four chimeras had a higher temperature optimum than TmxAcat, the most stable variant (T(opt)=80 degrees C) being the one in which both terminal segments came from TmxB. Further analysis suggests that the interaction between the N- and C-terminal segments has a disproportionately high contribution to the overall thermostability. The results may be generalizable to other enzymes where the N- and C-termini are in contact.

Biochemical characterization and sequence analysis of a xylanase produced by an exo-symbiotic bacterium of Gryllotalpa orientalis, Cellulosimicrobium sp. HY-12

An exo-symbiotic bacterium capable of hydrolyzing xylan was isolated from the gut of the mole cricket, Gryllotalpa orientalis, and identified as Cellulosimicrobium sp. HY-12. The xylanase (XylA( CspHY-12)) of this organism bound tightly to both DEAE and mono Q resins, and its molecular mass (M(r)) was about 39.0 kDa. The highest xylanase activity was observed at pH 6.0 and 60 degrees C. The enzyme was greatly suppressed by Ca(2+), Cu(2+), Co(2+), and Fe(2+) ions but not by Mg(2+) and Mn(2+). Although XylA( CspHY-12) was capable of hydrolyzing various types of xylosic compounds, it could not decompose carboxymethyl cellulose or xylobiose. The xylA (CspHY-12 ) gene consisted of an 1,188 bp open reading frame that encoded a polypeptide of 395 amino acids with a deduced molecular mass of 42,925 Da. The domain structure of XylA( CspHY-12) was most similar to those of the glycoside hydrolase (GH) family 10 endoxylanases. However its sequence identity with any of the enzymes in this family was below 52%. The results of this study suggest that the XylA( CspHY-12) is a new cellulase-free endo-beta-1,4-xylanase with some properties that are distinct from those of GH family 10.

Enzyme diversity of the cellulolytic system produced by Clostridium cellulolyticum explored by two-dimensional analysis: identification of seven genes encoding new dockerin-containing proteins

The enzyme diversity of the cellulolytic system produced by Clostridium cellulolyticum grown on crystalline cellulose as a sole carbon and energy source was explored by two-dimensional electrophoresis. The cellulolytic system of C. cellulolyticum is composed of at least 30 dockerin-containing proteins (designated cellulosomal proteins) and 30 noncellulosomal components. Most of the known cellulosomal proteins, including CipC, Cel48F, Cel8C, Cel9G, Cel9E, Man5K, Cel9M, and Cel5A, were identified by using two-dimensional Western blot analysis with specific antibodies, whereas Cel5N, Cel9J, and Cel44O were identified by using N-terminal sequencing. Unknown enzymes having carboxymethyl cellulase or xylanase activities were detected by zymogram analysis of two-dimensional gels. Some of these enzymes were identified by N-terminal sequencing as homologs of proteins listed in the NCBI database. Using Trap-Dock PCR and DNA walking, seven genes encoding new dockerin-containing proteins were cloned and sequenced. Some of these genes are clustered. Enzymes encoded by these genes belong to glycoside hydrolase families GH2, GH9, GH10, GH26, GH27, and GH59. Except for members of family GH9, which contains only cellulases, the new modular glycoside hydrolases discovered in this work could be involved in the degradation of different hemicellulosic substrates, such as xylan or galactomannan.

Marine glycosyl hydrolases in the hydrolysis and synthesis of oligosaccharides

The marine ecosystem can be considered a rather unexplored source of biological material (e.g. natural substances with therapeutic activity) and can also be a surprising source of enzymes carrying new and interesting catalytic activities to be applied in biocatalysis. The use of glycosyl hydrolases from marine environments dates back to the end of the 1960s and was mainly focused on the development of sensitive and reliable hydrolytic methods for the analysis of sugar chains. As a result not all the benefits of a particular enzymatic activity have been investigated, especially regarding the transglycosylation potential of these enzymes for the synthesis of glycosidic bonds. In this review, the potential of marine sources will be demonstrated reporting on the few examples found in literature for the synthesis and hydrolysis of biologically relevant oligosaccharides catalyzed by glycosyl hydrolases of marine origin. Particular emphasis is given to the synthesis of glycosidic bonds, which is easy by the use of glycosyl hydrolases. Further aspects considered in this review are applications of these biocatalysts for vegetal waste treatment in recovering useful materials, for structural identification and for preparation of target materials from new purified polysaccharides, for the synthesis or modification of food-related compounds and for glycobiology related studies.

Structural basis of the substrate subsite and the highly thermal stability of xylanase 10B from Thermotoga maritima MSB8

The crystal structure of xylanase 10B from Thermotoga maritima MSB8 (TmxB), a hyperthermostable xylanase, has been solved in its native form and in complex with xylobiose or xylotriose at 1.8 A resolution. In order to gain insight into the substrate subsite and the molecular features for thermal stability, we compared TmxB with family 10 xylanase structures from nine microorganisms. As expected, TmxB folds into a (beta/alpha)8-barrel structure, which is common among the glycoside hydrolase family 10. The enzyme active site and the environment surrounding the xylooligosaccharide of TmxB are highly similar to those of family 10 xylanases. However, only two xylose moieties were found in its binding pocket from the TmxB-xylotriose complex structure. This finding suggests that TmxB could be a potential biocatalyst for the large-scale production of xylobiose. The result of structural analyses also indicated that TmxB possesses some additional features that account for its thermostability. In particular, clusters of aromatic residues together with a lack of exposed hydrophobic residues are characteristic of the TmxB structure. TmxB has also a significant number of ion pairs on the protein surface that are not found in other thermophilic family 10 xylanases.

Biobleach boosting effect of recombinant xylanase B from the hyperthermophilic Thermotoga maritima on wheat straw pulp

The recombinant xylanase B (XynB) of Thermotoga maritima MSB8 was found to be highly specific towards xylans and exhibit very low activity towards carboxymethylcellulose in previous study. XynB was thermostable at neutral to alkaline pH region at 90 degrees C and retained more than 90% activity after 1 h over the pH range of pH 6.1 to 11.1. The suitability of XynB for use in the biobleaching of wheat straw pulp was investigated. Pretreatment of the pulp with XynB resulted in a substantial improvement in the bleachability of wheat straw pulp. When XynB at 10 U g(-1) was used to treat wheat straw pulp, it reduced pulp kappa number by 1.1 point, enhanced pulp brightness by 5.5% (% ISO) and improved other pulp properties, such as tensile index and breaking length. Biobleaching of wheat straw pulp with XynB saved active chlorine up to 34.5% while still maintaining the brightness at the control level. Besides, pretreatment of pulp with XynB was also effective at an alkaline pH as high as pH 10.1. This is the first report on the potential application of XynB from T. maritima MSB8 in the pulp and paper sector.

Fusion of family 2b carbohydrate-binding module increases the catalytic activity of a xylanase from Thermotoga maritima to soluble xylan

A family 2b carbohydrate-binding module from Streptomyces thermoviolaceus STX-II was fused at the carboxyl-terminus of XynB, a thermostable and single domain family 10 xylanase from Thermotoga maritima, to create a chimeric xylanase. The chimeric enzyme (XynB-CBM2b) was purified and characterized. It displayed a pH-activity profile similar to that of XynB and was stable up to 90 degrees C. XynB-CBM2b bound to insoluble birchwood and oatspelt xylan. Whereas its hydrolytic activities toward insoluble xylan and p-nitrophenyl-beta-xylopyranoside were similar to those of XynB, its activity toward soluble xylan was moderately higher than that of XynB.