The Discovery of a Multidomain Mannanase Containing Dual-Catalytic Domain of the Same Activity: Biochemical Properties and Synergistic Effect

In recent years, the wide application of mannan has driven the demand for the exploration of mannanase. As one of the main components of hemicellulose, mannan is an important polysaccharide that ruminants need to degrade and utilize, making rumen a rich source of mannanases. In this study, gene mining of mannanases was performed using bioinformatics, and potential dual-catalytic domain mannanases were heterologously expressed to analyze their properties. The hydrolysis pattern and enzymatic products were identified by liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS). A dual-catalytic domain mannanase Man26/5 with the same function as the substrate was successfully mined from the genome of cattle rumen microbiota. Compared to the single-catalytic domain, its higher thermal stability (≤50 °C) and catalytic efficiency confirm the synergistic effect between the two catalytic domains. It exhibited a unique "crab-like" structure where the CBM located in the middle is responsible for binding, and the catalytic domains at both ends are responsible for cutting. The exploration of its multidomain structure and synergistic patterns could provide a reference for the artificial construction and molecular modification of enzymes.

Thermophilic β-mannanases from bacteria: production, resources, structural features and bioengineering strategies

β-mannanases are pivotal enzymes that cleave the mannan backbone to release short chain mannooligosaccharides, which have tremendous biotechnological applications including food/feed, prebiotics and biofuel production. Due to the high temperature conditions in many industrial applications, thermophilic mannanases seem to have great potential to overcome the thermal impediments. Thus, structural analysis of thermostable β-mannanases is extremely important, as it could open up new avenues for genetic engineering, and protein engineering of these enzymes with enhanced properties and catalytic efficiencies. Under this scope, the present review provides a state-of-the-art discussion on the thermophilic β-mannanases from bacterial origin, their production, engineering and structural characterization. It covers broad insights into various molecular biology techniques such as gene mutagenesis, heterologous gene expression, and protein engineering, that are employed to improve the catalytic efficiency and thermostability of bacterial mannanases for potential industrial applications. Further, the bottlenecks associated with mannanase production and process optimization are also discussed. Finally, future research related to bioengineering of mannanases with novel protein expression systems for commercial applications are also elaborated.

Production of mannooligosaccharides from orange peel waste with β-mannanase expressed in Trichosporonoides oedocephalis

A large quantity of orange peel waste (OPW) is generated per year, yet effective biorefinery methods are lacking. In this study, Trichosporonoides oedocephalis ATCC 16958 was employed for hydrolyzing OPW to produce soluble sugars. Glycosyl hydrolases from Paenibacillussp.LLZ1 which can hydrolyze cellulose and hemicellulose were mined and characterized, with the highest β-mannanase activity of 39.1 U/mg at pH 6.0 and 50 ℃. The enzyme was overexpressed in T. oedocephalis and the sugar production was enhanced by 16 %. The accumulated sugar contains 57 % value-added mannooligosaccharides by the hydrolysis of mannans. The process was intensified by a pretreatment combining H2O2 submergence and steam explosion to remove potential inhibitors. The mannooligosaccharides yield of 6.5 g/L was achieved in flask conversion and increased to 9.7 g/L in a 5-L fermenter. This study improved the effectiveness of orange peel waste processing, and provided a hydrolysis-based methodology for the utilization of fruit wastes.

Engineered Alcaligenes sp. by chemical mutagen produces thermostable and acido-alkalophilic endo-1,4-β-mannanases for improved industrial biocatalyst

This study reported physicochemical properties of purified endo-1,4-β-mannanase from the wild type, Alcaligenes sp. and its most promising chemical mutant. The crude enzymes from fermentation of wild and mutant bacteria were purified by ammonium sulfate precipitation, ion exchange and gel-filtration chromatography followed by an investigation of the physicochemical properties of purified wild and mutant enzymes. β-mannanase from wild and mutant Alcaligenes sp. exhibited 1.75 and 1.6 purification-folds with percentage recoveries of 2.6 and 2.5% and molecular weights of 61.6 and 80 kDa respectively. The wild and mutant β-mannanase were most active at 40 and 50 °C with optimum pH 6.0 for both and were thermostable with very high percentage activity but the wild-type β-mannanase showed better stability over a broad pH activity. The β-mannanase activity from the parent strain was stimulated in the presence of Mn2+, Co2+, Zn2+, Mg2+ and Na+. Vmax and Km for the wild type and its mutant were found to be 0.747 U//mL/min and 5.2 × 10-4 mg/mL, and 0.247 U/mL/min and 2.47 × 10-4 mg/mL, respectively. Changes that occurred in the nucleotide sequences of the most improved mutant may be attributed to its thermo-stability, thermo-tolerant and high substrate affinity- desired properties for improved bioprocesses.

The Increase of Incomplete Degradation Products of Galactomannan Production by Synergetic Hydrolysis of β-Mannanase and α-Galactosidase

An integrated process to increase the yield of incomplete degradation products of galactomannan (GalM) especially for galactomanno-oligosaccharides (GalMOS) was suggested. Trichoderma reesei employed Avicel or GalMOS as a carbon source to produce β-mannanase or α-galactosidase independently, with a result of 3.78 ± 0.12 U/mL of β-mannanase activity and 2.45 ± 0.06 U/mL of α-galactosidase activity which were obtained, respectively. GalM in Sesbania seed was hydrolyzed simultaneously by a mixture of crude enzyme with β-mannanase and α-galactosidase at a dosage of 20 U/g GalM and 15 U/g GalM, respectively; the yields of incomplete degradation products of GalM (IDP-GalM) and GalMOS were 78.84% ± 3.14% and 30.94% ± 0.38%, respectively, which was beneficial to improve the biological activity of the incomplete degradation products. The role of α-galactosidase addition in mixture enzymes is to remove the galactose substituents from mannan backbone of GalM and alleviate the steric hindrance of β-mannanase hydrolysis.

Structure and function of Bs164 β-mannosidase from Bacteroides salyersiae the founding member of glycoside hydrolase family GH164

Recent work exploring protein sequence space has revealed a new glycoside hydrolase (GH) family (GH164) of putative mannosidases. GH164 genes are present in several commensal bacteria, implicating these genes in the degradation of dietary glycans. However, little is known about the structure, mechanism of action, and substrate specificity of these enzymes. Herein we report the biochemical characterization and crystal structures of the founding member of this family (Bs164) from the human gut symbiont Bacteroides salyersiae. Previous reports of this enzyme indicated that it has α-mannosidase activity, however, we conclusively show that it cleaves only β-mannose linkages. Using NMR spectroscopy, detailed enzyme kinetics of WT and mutant Bs164, and multiangle light scattering we found that it is a trimeric retaining β-mannosidase, that is susceptible to several known mannosidase inhibitors. X-ray crystallography revealed the structure of Bs164, the first known structure of a GH164, at 1.91 Å resolution. Bs164 is composed of three domains: a (β/α)8 barrel, a trimerization domain, and a β-sandwich domain, representing a previously unobserved structural-fold for β-mannosidases. Structures of Bs164 at 1.80-2.55 Å resolution in complex with the inhibitors noeuromycin, mannoimidazole, or 2,4-dinitrophenol 2-deoxy-2-fluoro-mannoside reveal the residues essential for specificity and catalysis including the catalytic nucleophile (Glu-297) and acid/base residue (Glu-160). These findings further our knowledge of the mechanisms commensal microbes use for nutrient acquisition.

A Recombinant β-Mannanase from Thermoanaerobacterium aotearoense SCUT27: Biochemical Characterization and Its Thermostability Improvement

β-Mannanase was expressed in Thermoanaerobacterium aotearoense SCUT27 induced by locust bean gum (LBG). The open reading frame encoding a GH26 β-mannanase was identified and encoded a preprotein of 515 amino acids with a putative signal peptide. The enzyme without a signal sequence (Man25) was overexpressed in Escherichia coli with a specific activity of 1286.2 U/mg. Moreover, a facile method for β-mannanase activity screening was established based on agar plates. The optimum temperature for the purified Man25 using LBG as a substrate was 55 °C. The catalytic activity and thermostability of Man25 displayed a strong dependence on calcium ions. Through saturation mutagenesis at the putative Ca²⁺ binding sites in Man25, the best mutant ManM3-3 (D143A) presented improvements in thermostability with 3.6-fold extended half-life at 55 °C compared with that of the wild-type. The results suggest that mutagenesis at metal binding sites could be an efficient approach to increase enzyme thermostability.

Regulation of hyperglycemia in diabetic mice by autolysates from β-mannanase-treated brewer's yeast

BACKGROUND

Diabetes mellitus is a serious chronic disease, characterized by hyperglycemia. This study administered either β-mannanase-treated yeast cell autolysis supernatant (YCS) or yeast cell-wall residues after autolysis (YCR) to investigate their influence on the alleviation of diabetes in a diabetic mouse model.

RESULTS

Application of either YCS or YCR led to body weight gain, blood glucose reduction, and an improvement in lipid composition in the diabetic mice. Administration of YCS was more effective in inhibiting oxidative stress than YCR. The expression of PPARα and CPT1α was enhanced, improving lipid biosynthesis, and Trx1 and HIF-1-α genes were downregulated due to the activation of thioredoxin following the interventions, indicating that the processes of lipid metabolism and oxidative stress were heavily involved in the reduction of diabetic characteristics following the interventions. The current study revealed that consumption of YCR also led to a reduction in hyperglycemia, this being associated with its richness in mineral elements, such as chromium and selenium.

CONCLUSION

This study may highlight the potential of both YCS and YCR as functional ingredients in dietary formula for improving diabetic syndromes. © 2019 Society of Chemical Industry.

Characterization of Thermostable and Chimeric Enzymes via Isopeptide Bond-Mediated Molecular Cyclization

Mannooligosaccharides are released by mannan-degrading endo-β-1,4-mannanase and are known as functional additives in human and animal diets. To satisfy demands for biocatalysis and bioprocessing in crowed environments, in this study, we employed a recently developed enzyme-engineering system, isopeptide bond-mediated molecular cyclization, to modify a mesophilic mannanase from Bacillus subtilis. The results revealed that the cyclized enzymes showed enhanced thermostability and ion stability and resilience to aggregation and freeze-thaw treatment by maintaining their conformational structures. Additionally, by using the SpyTag/SpyCatcher system, we generated a mannanase-xylanase bifunctional enzyme that exhibited a synergistic activity in substrate deconstruction without compromising substrate affinity. Interestingly, the dual-enzyme ring conformation was observed to be more robust than the linear enzyme but inferior to the single-enzyme ring conformation. Taken together, these findings provided new insights into the mechanisms of molecular cyclization on stability improvement and will be useful in the production of new functional oligosaccharides and feed additives.

Backbone 1H, 13C, and 15N resonance assignments of BoMan26A, a β-mannanase of the glycoside hydrolase family 26 from the human gut bacterium Bacteroides ovatus

Bacteroides ovatus is a member of the human gut microbiota. The importance of this microbial consortium involves the degradation of complex dietary glycans mainly conferred by glycoside hydrolases. In this study we focus on one such catabolic glycoside hydrolase from B. ovatus. The enzyme, termed BoMan26A, is a β-mannanase that takes part in the hydrolytic degradation of galactomannans. The crystal structure of BoMan26A has previously been determined to reveal a TIM-barrel like fold, but the relation between the protein structure and the mode of substrate processing has not yet been studied. Here we report residue-specific assignments for 95% of the 344 backbone amides of BoMan26A. The assignments form the basis for future studies of the relationship between substrate interactions and protein dynamics. In particular, the potential role of loops adjacent to glycan binding sites is of interest for such studies.

Insight into the Thermophilic Mechanism of a Glycoside Hydrolase Family 5 β-Mannanase

To study the molecular basis for thermophilic β-mannanase of glycoside hydrolase family 5, two β-mannanases, TlMan5A and PMan5A, from Talaromyces leycettanus JCM12802 and Penicillium sp. WN1 were used as models. The four residues, His112 and Phe113, located near the antiparallel β-sheet at the barrel bottom and Leu375 and Ala408 from loop 7 and loop 8 of PMan5A, were inferred to be key thermostability contributors through module substitution, truncation, and site-directed mutagenesis. The effects of these four residues on the thermal properties followed the order H112Y > A408P > L375H > F113Y and were strongly synergetic. These results were interpreted structurally using molecular dynamics (MD) simulations, which showed that improved hydrophobic interactions in the inner wall of the β-barrel and the rigidity of loop 8 were caused by the outside domain of the barrel bottom and proline, respectively. The TIM barrel bottom and four specific residues responsible for the thermostability of GH5 β-mannanases were elucidated.

Galactomannan Degrading Enzymes from the Mannan Utilization Gene Cluster of Alkaliphilic Bacillus sp. N16-5 and Their Synergy on Galactomannan Degradation

Two glycoside hydrolases encoded by the mannan utilization gene cluster of alkaliphilic Bacillus sp. N16-5 were studied. The recombinant Gal27A (rGal27A) hydrolyzed both galactomannans and oligo-galactomannans to release galactose, while the recombinant Man113A (rMan113A) showed poor activity toward galactomannans, but it hydrolyzed manno-oligosaccharides to release mannose and mannobiose. rGal27A showed synergistic interactions with rMan113A and recombinant β-mannanase ManA (rManA), which is also from Bacillus sp. N16-5, in galactomannan degradation. The synergy degree of rGal27A and rManA on hydrolysis of locust bean gum and guar gum was 1.13 and 2.21, respectively, and that of rGal27A and rMan113A reached 2.00 and 2.68. The main products of galactomannan hydrolyzed by rGal27A and rManA simultaneously were galactose, mannose, mannobiose, and mannotriose, while those of galactomannan hydrolyzed by rGal27A and rMan113A were galactose and mannose. The yields of mannose, mannobiose, and mannotriose dramatically increased compared with the hydrolysis in the presence of rManA or rMan113A alone.

Structural basis of exo-β-mannanase activity in the GH2 family

The classical microbial strategy for depolymerization of β-mannan polysaccharides involves the synergistic action of at least two enzymes, endo-1,4-β-mannanases and β-mannosidases. In this work, we describe the first exo-β-mannanase from the GH2 family, isolated from Xanthomonas axonopodis pv. citri (XacMan2A), which can efficiently hydrolyze both manno-oligosaccharides and β-mannan into mannose. It represents a valuable process simplification in the microbial carbon uptake that could be of potential industrial interest. Biochemical assays revealed a progressive increase in the hydrolysis rates from mannobiose to mannohexaose, which distinguishes XacMan2A from the known GH2 β-mannosidases. Crystallographic analysis indicates that the active-site topology of XacMan2A underwent profound structural changes at the positive-subsite region, by the removal of the physical barrier canonically observed in GH2 β-mannosidases, generating a more open and accessible active site with additional productive positive subsites. Besides that, XacMan2A contains two residue substitutions in relation to typical GH2 β-mannosidases, Gly439 and Gly556, which alter the active site volume and are essential to its mode of action. Interestingly, the only other mechanistically characterized mannose-releasing exo-β-mannanase so far is from the GH5 family, and its mode of action was attributed to the emergence of a blocking loop at the negative-subsite region of a cleft-like active site, whereas in XacMan2A, the same activity can be explained by the removal of steric barriers at the positive-subsite region in an originally pocket-like active site. Therefore, the GH2 exo-β-mannanase represents a distinct molecular route to this rare activity, expanding our knowledge about functional convergence mechanisms in carbohydrate-active enzymes.

Effect of β-mannanase domain from Trichoderma reesei on its biochemical characters and synergistic hydrolysis of sugarcane bagasse

BACKGROUND

β-mannanase is a key enzyme for hydrolyzing mannan, a major constituent of hemicellulose, which is the second most abundant polysaccharide in nature. Different structural domains greatly affect its biochemical characters and catalytic efficiency. However, the effects of linker and carbohydrate-binding module (CBM) on β-mannanase from Trichoderma reesei (Man1) have not yet been fully described. The present study aimed to determine the influence of different domains on the expression efficiency, biochemical characteristics and hemicellulosic deconstruction of Man1.

RESULTS

The expression efficiency was improved after truncating CBM. Activities of Man1 and Man1ΔCBM (CBM) in the culture supernatant after 168 h of induction were 34.5 and 42.9 IU mL^-1 , although a value of only 0.36 IU mL^-1 was detected for Man1ΔLCBM (lacking CBM and linker). Man1 showed higher thermostability than Man1ΔCBM at low temperature, whereas Man1ΔCBM had a higher specificity for galactomannan (K_m  = 2.5 mg mL^-1 ) than Man1 (K_m  = 4.0 mg mL^-1 ). Both Man1 and Man1ΔCBM could synergistically improve the hydrolysis of cellulose, galactomannan and pretreated sugarcane bagasse, with a 10-30% improvement of the reducing sugar yield.

CONCLUSION

Linker and CBM domains were vital for mannanase activity and expression efficiency. CBM affected the thermostability and adsorption ability of Man1. The results obtained in the present study should help guide the rational design and directional modification of Man with respect to improving its catalytic efficiency. © 2017 Society of Chemical Industry.

Efficient Coproduction of Mannanase and Cellulase by the Transformation of a Codon-Optimized Endomannanase Gene from Aspergillus niger into Trichoderma reesei

Cellulase and mannanase are both important enzyme additives in animal feeds. Expressing the two enzymes simultaneously within one microbial host could potentially lead to cost reductions in the feeding of animals. For this purpose, we codon-optimized the Aspergillus niger Man5A gene to the codon-usage bias of Trichoderma reesei. By comparing the free energies and the local structures of the nucleotide sequences, one optimized sequence was finally selected and transformed into the T. reesei pyridine-auxotrophic strain TU-6. The codon-optimized gene was expressed to a higher level than the original one. Further expressing the codon-optimized gene in a mutated T. reesei strain through fed-batch cultivation resulted in coproduction of cellulase and mannanase up to 1376 U·mL^-1 and 1204 U·mL^-1, respectively.

Coproduction of protease and mannanase from Bacillus nealsonii PN-11 in solid state fermentation and their combined application as detergent additives

Bacillus nealsonii PN-11 produces thermo-alkalistable mannanase and protease active in wide temperature and pH range. Optimization of coproduction of protease and mannanase from this strain and application of cocktail of these enzymes as detergent additives were studied. On optimization mannanase yield of 834Ug^-1 (11.12 fold increase) and protease yield of 70Ug^-1 (4.7 fold increase) could be obtained in a single fermentation. Purification and characterization of mannanase have been done earlier and protease was done during this study and has a molecular mass of 48kDa. pH and temperature optima for protease were 10.0 and 65°C respectively. It was completely stable at 60°C for 3h and retained >80% of activity at pH 11.0 for 1h. Both the enzymes were compatible with detergents individually and in a combination. The wash performance of the detergent on different type of stains improved when protease or mannanase were used individually. However destaining was more efficient when a combination of mannanase and protease was used.

Mannanase Man23 mutant library construction based on a novel cell-free protein expression system

BACKGROUND

Mannanases are important enzymes which are widely used as a tool in agriculture and food industries. To improve the performance of mannanase Man23, a mutant library was created with rational design, and mutations were introduced on loops around the catalytic region. The Brevibacillus brevis B16 cell-free system which was created in this experiment provided the ability to express the mutant library efficiently. The activities of mutants were measured with a multi-volume spectrophotometer.

RESULTS

The mutant Man1606 gained from this system is a sextet which has mutations of N146G, S147H, S156P, T157Y, Q206S and T249H simultaneously on loops 6, 8 and 10. Man1606 showed higher activity and stability than Man23. The optimal temperature of Man1606 rose by 5 °C (from 55 to 60 °C) and the optimal pH increased slightly but its range became broader.

CONCLUSION

This experiment demonstrated the B. brevis cell-free system shortens the expression time and is an efficient tool for mannanase engineering. © 2016 Society of Chemical Industry.

Enhanced mannan-derived fermentable sugars of palm kernel cake by mannanase-catalyzed hydrolysis for production of biobutanol

Catalytic depolymerization of mannan composition of palm kernel cake (PKC) by mannanase was optimized to enhance the release of mannan-derived monomeric sugars for further application in acetone-butanol-ethanol (ABE) fermentation. Efficiency of enzymatic hydrolysis of PKC was studied by evaluating effects of PKC concentration, mannanase loading, hydrolysis pH value, reaction temperature and hydrolysis time on production of fermentable sugars using one-way analysis of variance (ANOVA). The ANOVA results revealed that all factors studied had highly significant effects on total sugar liberated (P<0.01). The optimum conditions for PKC hydrolysis were 20% (w/v) PKC concentration, 5% (w/w) mannanase loading, hydrolysis pH 4.5, 45°C temperature and 72h hydrolysis time. Enzymatic experiments in optimum conditions revealed total fermentable sugars of 71.54±2.54g/L were produced including 67.47±2.51g/L mannose and 2.94±0.03g/L glucose. ABE fermentation of sugar hydrolysate by Clostridium saccharoperbutylacetonicum N1-4 resulted in 3.27±1.003g/L biobutanol.

[Expression in Aspergillus niger and characterization of β-mannanases from Stachybotrys chartarum]

OBJECTIVE

Using Aspergillus niger as host to express β-mannanases from Stachybotrys chartarum.

METHODS

Through sequence analysis of Stachybotrys chartarum genome, two β-mannanase genes (s16942 and s331) were identified. The primers were designed based on the DNA sequence and the β-mannanase genes (s16942 and s331) were obtained, and then inserted to the vector pGm. The expression plasmids were transferred into Aspergillus niger. β-mannanase producing strains (G1-pGm-s16942 and G1-pGm-s331) were isolated after screening several transformants using amdS selection plates and confirmed by PCR fragment sequencing.

RESULTS

The molecular weight of the enzymes from G1-pGm-s16942 and G1-pGm-s331 were about 48 kDa and 60 kDa respectively by SDS-PAGE gel analysis, and the recombinant proteins did not present in the negative control. Assays of enzymatic property using the crude enzyme preparations indicated that the enzyme from G1-pGm-s16942 exhibited maximum activity (521 U/mL) under the optimum.

CONCLUSION

This was the first study of the heterologous expression of the β-mannanase genes from Stachybotrys chartarum in Aspergillus niger host and the β-mannanase genes could be expressed successfully with high activities and protein titers.

N-terminal truncation contributed to increasing thermal stability of mannanase Man1312 without activity loss

BACKGROUND

The disordered residues on distal loops affect the molecular structural stability and on some occasions have regulatory roles in catalytic reaction. To increase understanding of the influence of distal residue mutation, this study explored the thermostability and enzymatic activity of mannanase Man1312 deletion mutants. The focus was on residues located on the N-terminal region because they are more disordered and changeable. The effects of N-terminal truncation on enzymatic activity and thermal dynamics were investigated by spectrophotometry, circular dichroism and differential scanning calorimetry assays.

RESULTS

The deletion mutants on V3, N7 and Q11 showed a marked increase in stability, while the enzymatic activity was significantly improved when triplet deletion was carried out. Triplet deletion MandVNQ showed around double the stability of its corresponding single-site and double-site deletion mutants. The Tm value of MandVNP was about 8 °C higher than that of Man1312. MandVNP had improved characteristics of Topt by 10 °C, t1/2 by 10 min and catalytic activity by 11% in comparison with Man1312. Analysis of spectra and modeling showed that MandVNQ had increased helix and strand contents.

CONCLUSION

N-terminal truncation had positive effects on the thermostability and activity of mannanase.

[Correlation between superior enzymatic properties of β-mannanase AuMan5A/Af and its residue Asp(320)]

OBJECTIVE

AuMan5A is a glycoside hydrolase (GH) family 5 β-mannanase from Aspergillus usamii. To improve its enzymatic properties, we have previously constructed a mutant with loop substitution, AuMan5A/Af, by substituting a loop of seven residues (316KSPDGGN322) in its substrate binding groove with the corresponding region (PSPNDHF) of A. fumigatus GH family 5 β-mannanase. To reveal the correlation between the superior enzymatic properties of AuMan5A/Af and its residue Asp320, site-directed mutagenesis was used to obtain a new mutant enzyme AuMan5A/Af(D320G).

METHODS

Using megaprimer PCR method, we constructed a new mutant-encoding gene, Auman5A/Af(D320G) by mutating an Asp320 -encoding codon GAC of Auman5A/Af into a Gly320 -encoding GGT. Then, Auman5A/Af(D320G) was extracellularly expressed in Pichia pastoris GS115, and the enzymatic properties of the expressed product were analyzed.

RESULTS

Analytical results indicated that the optimal and melting temperature of AuMan5A/Af(D320G) was 70.0 degrees C and 71.5 degrees C, repectively, higher than those of AuMan5A (T(opt) = 65.0 degrees C, T(m) = 64.5 degrees C) and lower than those of AuMan5A/Af (T(opt) = 75.0 degrees C, T(m) =76.6 degrees C); its half-life at 70.0 degrees C was 40 min, 10 min longer than that of AuMan5A but greatly shorter than 480 min of AuMan5A/Af. Besides, its specific activity was 2.7 fold and 0.3 fold that of AuMan5A and AuMan5A/Af, respectively, and its catalytic efficiency (k(cat)/K(m)) was 3.9 fold and 0.3 fold that of AuMan5A and AuMan5A/Af.

CONCLUSION

The mutation of ASP320 into Gly320 greatly affected the temperature characteristics and catalytic activity of AuMan5A/Af, demonstrating that Asp320 plays an improtant role in temperature characteristics, specific activity and catalytic efficiency improving of AuMan5A after loop substitution.

[Characterization of β-1, 4-mannanase from Bacillus pumilus and heterologous expression in Lactobacillus casei]

OBJECTIVE

Lactobacillus casei is widely used in food production and feed industry. The aim of this study was to construct the recombinant expression mannanase Lb. casei.

METHODS

The mature peptide gene of β-1,4-mannanase from Bacillus pumilus was cloned into expression vectors pELX1 and pELSH, then electroporated into Lb. casei, establishing an intracellular and a secretion expression mannanase Lb. casei respectively.

RESULTS

After incubation, the specific activity of β-1,4-mannanase was 23 U/mg whole cell protein for intracellular expression and 8.8 U/mL for secretion expression in supernatant.

CONCLUSION

Mannanase gene expression in Lb. casei provides application prospect and deserves further study.

[Alkaline-adapted beta-mannanase of Bacillus pumilus: gene heterologous expression and enzyme characterization]

OBJECTIVE

We expressed a novel alkaline-adapted beta-mannanase gene and characterized the enzyme for potential industrial applications.

METHODS

We obtained a mannanase gene (named man(B)) from Bacillus pumilus Nsic2 and expressed the gene man(B) in Escherichia coli and Bacillus subtilis. Furthermore, we characterized the enzyme.

RESULTS

The gene man(B) had an open reading frame of 1104 bp that encoded a polypeptide of 367-amino-acid beta-mannanase (Man(B)). The protein sequence showed the highest identity with the beta-mannanase from B. pumilus CCAM080065. We expressed the gene man(B) in E. coli BL21 (DE3) with the enzyme activity of 11021.3 U/mL. Compared with other mannanases, Man(B) showed higher stability under alkaline conditions and was stable at pH6.0 -9.0. The specific activity of purified Man(B) was 4191 ± 107 U/mg. The K(m) and V(max) values of purified Man(B) were 35.7 mg/mL and 14.9 μmol/(mL x min), respectively. Meanwhile, we achieved recombinant protein secretion expression in B. subtilis WB800N.

CONCLUSION

We achieved heterologous expression of the gene man(B) and characterized its enzyme. The alkaline-adapted Man(B) showed potential value in industrial applications due to its pH stability.

Degradation of konjac glucomannan by Thermobifida fusca thermostable β-mannanase from yeast transformant

Native konjac glucomannan was used as the substrate for thermophilic actinomycetes, Thermobifida fusca BCRC19214, to produce β-mannanase. The β-mannanase was purified and five internal amino acid sequences were determined by LC-MS/MS. These sequences had high homology with the β-mannanase from T. fusca YX. The tfm gene which encoded the β-mannanase was cloned, sequenced and heterologous expressed in Yarrowia lipolytica P01 g expression system. Recombinant heterologous expression resulted in extracellular β-mannanase production at levels as high as 3.16 U/ml in the culture broth within 48 h cultivation. The recombinant β-mannanase from Y. lipolytica transformant had superior thermal property. The optimal temperature of the recombinant β-mannanase from Y. lipolytica transformant (pYLSC1-tfm) was 80°C. When native konjac glucomannan was incubated with the recombinant β-mannanase from Y. lipolytica transformant (pYLSC1-tfm) at 50°C, there was a fast decrease of viscosity happen during the initial phase of reaction. This viscosity reduction was accompanied by an increase of reducing sugars. The surface of konjac glucomannan film became smooth. After 24h of treatment, the DPw of native konjac glucomannan decreased from 6,435,139 to 3089.

Mannans and endo-β-mannanases (MAN) in Brachypodium distachyon: expression profiling and possible role of the BdMAN genes during coleorhiza-limited seed germination

Immunolocalization of mannans in the seeds of Brachypodium distachyon reveals the presence of these polysaccharides in the root embryo and in the coleorhiza in the early stages of germination (12h), decreasing thereafter to the point of being hardly detected at 27h. Concurrently, the activity of endo-β-mannanases (MANs; EC 3.2.1.78) that catalyse the hydrolysis of β-1,4 bonds in mannan polymers, increases as germination progresses. The MAN gene family is represented by six members in the Brachypodium genome, and their expression has been explored in different organs and especially in germinating seeds. Transcripts of BdMAN2, BdMAN4 and BdMAN6 accumulate in embryos, with a maximum at 24-30h, and are detected in the coleorhiza and in the root by in situ hybridization analyses, before root protrusion (germination sensu stricto). BdMAN4 is not only present in the embryo root and coleorhiza, but is abundant in the de-embryonated (endosperm) imbibed seeds, while BdMAN2 and BdMAN6 are faintly expressed in endosperm during post-germination (36-42h). BdMAN4 and BdMAN6 transcripts are detected in the aleurone layer. These data indicate that BdMAN2, BdMAN4 and BdMAN6 are important for germination sensu stricto and that BdMAN4 and BdMAN6 may also influence reserve mobilization. Whether the coleorhiza in monocots and the micropylar endosperm in eudicots have similar functions, is discussed.

Expression of a β-mannosidase from Paenibacillus polymyxa A-8 in Escherichia coli and characterization of the recombinant enzyme

Paenibacillus polymyxa A-8, which secretes β-mannosidase, was isolated from the soil sample under a pine tree located in the "Laoban" mountain region of Sichuan, China. The β-mannosidase gene (MANB) was isolated from P. polymyxa A-8, using primers according to the complete genome. The MANB (2,550 bp) encoding 849 amino acid residues was expressed in Escherichia coli. The specific activities of β-mannosidase produced by P. polymyxa A-8 and E. coli pET30a-MANB were 12 nkat/mg and 635 nkat/mg respectively. SDS-PAGE analysis indicated that the molecular mass of the recombinant MANB was approximately 96 kDa. The recombinant MANB was active between pH 7.0-8.5 with the maximum activity at pH 7.0. It had good pH stability and adaptability. The MANB had the optimal temperature of 35°C and was relatively stable at 35-40°C. In addition, the MANB activity was enhanced by K+, Ca2+, Mn2+, and Mg2+ and inhibited by Zn2+, Cu2+, and Hg2+.

An enzyme-responsive controlled release system of mesoporous silica coated with Konjac oligosaccharide

A simple and green method to fabricate an ingenious enzyme-responsive drug controlled release system was presented. Mesoporous silica material (mSiO2) 100 nm in size was used as the host, and Konjac oligosaccharide (KOGC) was employed to seal the nanopores of mSiO2 to inhibit the drug release. Rhodamine B was used as the model cargo to reveal the release behavior of the system. The KOGC-modified mSiO2 (mSiO2@KOGC) retains the drug until it reaches the colonic environment where bacteria secrete enzymes (β-mannanase) can degrade KOGC and make drug release. The amount of KOGC and enzyme can be used to adjust the release performance. And all the release behaviors fit the two-step Higuchi model, which predominate by KOGC degradation and mesoporous structure, respectively. With well bioactivity and selectivity, the system has potential application as an oral medicine carrier for treating intestinal disease.

Thermostable recombinant β-(1→4)-mannanase from C. thermocellum: biochemical characterization and manno-oligosaccharides production

Functional attributes of a thermostable β-(1→4)-mannanase were investigated from Clostridium thermocellum ATCC 27405. Its sequence comparison the exhibited highest similarity with Man26B of C. thermocellum F1. The full length CtManf and truncated CtManT were cloned in the pET28a(+) vector and expressed in E. coli BL21(DE3) cells, exhibiting 53 kDa and 38 kDa proteins, respectively. On the basis of the substrate specificity and hydrolyzed product profile, CtManf and CtManT were classified as β-(1→4)-mannanase. A 1.5 fold higher activity of both enzymes was observed by Ca(2+) and Mg(2+) salts. Plausible mannanase activity of CtManf was revealed by the classical hydrolysis pattern of carob galactomannan and the release of manno-oligosaccharides. Notably highest protein concentrations of CtManf and CtManT were achieved in tryptone yeast extract (TY) medium, as compared with other defined media. Both CtManf and CtManT displayed stability at 60 and 50 °C, respectively, and Ca(2+) ions imparted higher thermostability, resisting their melting up to 100 °C.

Preliminary X-ray diffraction analysis of thermostable β-1,4-mannanase from Aspergillus niger BK01

β-1,4-Mannanase (β-mannanase) is a key enzyme in decomposing mannans, which are abundant components of hemicelluloses in the plant cell wall. Therefore, mannan hydrolysis is highly valuable in a wide array of industrial applications. β-Mannanase isolated from Aspergillus niger BK01 (ManBK) was classified into glycoside hydrolase family GH5. ManBK holds great potential in biotechnological applications owing to its high thermostability. Here, ManBK was expressed and purified in Pichia pastoris and the recombinant protein was crystallized. Crystals belonging to the orthorhombic space group C222₁, with unit-cell parameters a=93.58, b=97.05, c=147.84 Å, were obtained by the sitting-drop vapour-diffusion method and diffracted to 1.57 Å resolution. Structure determination using molecular-replacement methods is in progress.

Crystallization and preliminary X-ray crystallographic analysis of recombinant β-mannosidase from Aspergillus niger

β-Mannosidase (EC 3.2.1.25) is an important exoglycosidase specific for the hydrolysis of terminal β-linked mannoside in various oligomeric saccharide structures. β-Mannosidase from Aspergillus niger was expressed in Pichia pastoris and purified to clear homogeneity. β-Mannosidase was crystallized in the presence of D-mannose and the crystal diffracted to 2.41 Å resolution. The crystal belonged to space group P1, with unit-cell parameters a=62.37, b=69.73, c=69.90 Å, α=108.20, β=101.51, γ=103.20°. The parameters derived from the data collection indicate the presence of one molecule in the asymmetric unit.

Structure of β-1,4-mannanase from the common sea hare Aplysia kurodai at 1.05 Å resolution

β-1,4-Mannanase (EC 3.2.1.78) catalyzes the hydrolysis of β-1,4-glycosidic bonds within mannan, a major constituent group of the hemicelluloses. Bivalves and gastropods possess β-1,4-mannanase and may degrade mannan in seaweed and/or phytoplankton to obtain carbon and energy using the secreted enzymes in their digestive systems. In the present study, the crystal structure of AkMan, a gastropod β-1,4-mannanase prepared from the common sea hare Aplysia kurodai, was determined at 1.05 Å resolution. This is the first report of the three-dimensional structure of a gastropod β-1,4-mannanase. The structure was compared with bivalve β-1,4-mannanase and the roles of residues in the catalytic cleft were investigated. No obvious binding residue was found in subsite +1 and the substrate-binding site was exposed to the molecular surface, which may account for the enzymatic properties of mannanases that can digest complex substrates such as glucomannan and branched mannan.

Cloning and bioinformatic analysis of an acidophilic beta-mannanase gene, Anman5A, from Aspergillus niger LW-1

Using 3' and 5' rapid amplification of cDNA ends (RACE) techniques, the full-length cDNA sequence of the AnmanSA, a gene that encodes an acidophilic beta-mannanase of Aspergillus niger LW-1 (abbreviated to AnMan5A), was identified from the total RNA. The cDNA sequence was 1417 bp in length, harboring 5'- and 3'-untranslated regions, as well as an open reading frame (ORF) which encodes a 21-aa signal peptide, a 17-aa propeptide and a 345-aa mature peptide. Based on the topology of the phylogenetic tree of beta3-mannanases from glycoside hydrolase (GH) family 5, the AnMan5A belongs to the subfamily 7 of the GH family 5. Its 3D structure was modeled by the bitemplate-based method using both MODELLER 9.9 and SALIGN programs, based on the known beta-mannanase crystal structures of Trichoderma reesei (1QNO) and Lycopersicon esculentum (1RH9) from the GH family 5. In addition, the complete DNA sequence of the Anman5A was amplified from the genomic DNA using the pUCm-T vector-mediated PCR and conventional PCR methods. The DNA sequence was 1825 bp in length, containing a 5'-flanking regulatory region, 2 introns and 3 exons when compared with the full-length cDNA.

Cloning and functional expression of an acidophilic β-mannanase gene (Anman5A) from Aspergillus niger LW-1 in Pichia pastoris

A cDNA fragment of the Anman5A, a gene that encodes an acidophilic β-mannanase of Aspergillus niger LW-1 (abbreviated as AnMan5A), was cloned and functionally expressed in Pichia pastoris . Homology alignment of amino acid sequences verified that the AnMan5A belongs to the glycoside hydrolase (GH) family 5. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) assay demonstrated that the recombinant AnMan5A (reAnMan5A), a N-glycosylated protein with an apparent molecular weight of 52.0 kDa, was secreted into the medium. The highest reAnMan5A activity expressed by one P. pastoris transformant, labeled as GSAnMan4-12, reached 29.0 units/mL. The purified reAnMan5A displayed the highest activity at pH 3.5 and 70 °C. It was stable at a pH range of 3.0-7.0 and at a temperature of 60 °C or below. Its activity was not significantly affected by an array of metal ions and ethylenediaminetetraacetic acid (EDTA). The K(m) and V(max) of the reAnMan5A, toward locust bean gum, were 1.10 mg/mL and 266.7 units/mg, respectively.

High-level production of a cold-active B-mannanase from Bacillus subtilis BS5 and its molecular cloning and expression

Mannanases can be useful in the food, feed, pulp and paper industries. In this research a Bacillus subtilis strain (named Bs5) which produced high-level beta-mannanase was isolated. Maximum level of beta-mannanase (1231.41 U/ml) was reached when Bacillus subtilis Bs5 was grown on konjac powder as the carbon source for nine hours at 32 degrees C. The beta-mannanase was a typical cold-active enzyme and its optimal temperature of 35 degrees C was the lowest among those of the known mannanases from bacteria. In addition, the optimal pH was 5.0 and much wide pH range from 3.0-8.0 was also observed in the beta-mannanase. These properties make the beta-mannanase more attractive for biotechnological applications. The DNA sequence coding the beta-mannanase was cloned and the open reading frame consisted of 1089 bp encoding 362 amino acids. A phylogenetic tree of the beta-mannanase based on the similarity of amino acid sequences revealed that the beta-mannanase formed a cluster with the beta-mannanases of Bacillus subtilis, which was separated from the mannanases of fungi and other bacteria. The beta-mannanase gene could be expressed in Escherichia coli and the recombinant beta-mannanase was characterized by Western blot. This study provided a new source of carbohydrate hydrolysis enzyme with novel characteristics from Bacillus subtilis.

[Purification and characterization of mannanase from an alkaliphilic mannanase producing bacterium HMTS15]

OBJECTIVE

To isolate and identify an alkaliphilic mannanase producing bacterium, purify and characterize mannanase thereof.

METHODS

Mannanase-producing alkaliphilic bacterium HMTS15 was isolated by alkaline agar with konjak from water sample of Hamatai Lake in Inner Mongolia, China. The morphological, biochemical and physiological characteristics and 16S rRNA gene were analyzed to identify the taxonomic position of strain HMTS15. Mannanase produced by strain HMTS15 was purified by four steps including (NH4)2SO4 precipitation, cellulose DEAE-sepharose, twice Superdex 200. The enzyme properties including optimal temperature, optimal pH, thermal stability, pH stability, NaCl tolerance, metal ion tolerance, EDTA and SDS tolerance were tested.

RESULTS

Strain HMTS15 was Gram-positive rod. Its growth pH ranged from 7.0 to 11.0 and growth temperature ranged from 10 degrees C to 45 degrees C. The G + C content of the DNA was 40 mol%. Phylogenetic analyses based on 16S rRNA gene sequence comparisons indicated that strain HMTS15 was a member of Bacillus. The extracellular mannanase from strain HMTS15 was purified as a single band with molecular weight of about 45 kD on SDS-PAGE. The optimal catalytic activity was showed at 75 degrees C and pH 10. The mananase was stable up to 60 degrees C and retained about 60% residual activity at 65 degrees C for 30 min. The ions Fe2+, Mn2+, Co2+, Zn2+, Ag+, Hg2+ and EDTA inhibited the acitivity of the mannanase.

CONCLUSION

Polyphasic taxonomy revealed that strain HTMS15 was a new member of Bacillus agaradhaerens. The alkaline mannanase produced by strain HMTS15 hold the valuable property in stability at high temperature and broad range of pH.

Molecular cloning and biochemical characterization of an endo-β-mannanase gene from soybean for soybean meal improvement

Soybean meal is the most commonly used protein source in animal feeds. Among the undesirable attributes of soybean meal is the high level of β-mannan, which was determined to be detrimental to the growth performance of animals. β-Mannan is a type of hemicellulose in the plant cell wall and can be hydrolyzed by endo-β-mannanase. The goal of this study is to isolate and characterize an endo-β-mannanase gene from soybean that can be used for genetic improvement of soybean meal. From the sequenced soybean genome, 21 putative endo-β-mannanase genes were identified. On the basis of their relatedness to known functional plant endo-β-mannanases, four soybean endo-β-mannanase genes (GmMAN1 to GmMAN4) were chosen for experimental analysis. GmMAN1 and GmMAN4 showed expression in the soybean tissue examined, and their cDNAs without the sequences for signal peptide were cloned and expressed in Escherichia coli to produce recombinant enzymes. Only GmMAN1 showed endo-β-mannanase hydrolase activity. Further gene expression analysis showed that GmMAN1 is specifically expressed in cotyledons of seedlings, suggesting a role of GmMAN1 in degrading mannan-rich food reserves during soybean seedling establishment. Purified recombinant GmMAN1 exhibited an apparent K(m) value of 34.9 mg/mL. The catalytic efficiency (k(cat)/K(m)) of GmMAN1 was determined to be 0.7 mL/(mg·s). GmMAN1 was also shown to be active in hydrolyzing the β-mannan-rich cell wall of soybean seeds.

Crystallization and preliminary crystallographic analysis of β-mannanase from Bacillus licheniformis

The mannan endo-1,4-β-mannosidase (ManB) from Bacillus licheniformis strain DSM13 was overexpressed in Escherichia coli. Purification of the thermostable and alkali-stable recombinant mannanase yielded approximately 50 mg enzyme per litre of culture. Crystals were grown by hanging-drop vapour diffusion using a precipitant solution consisting of 12%(w/v) PEG 8000, 0.2 M magnesium acetate tetrahydrate and 0.1 M MES pH 6.5. The protein crystallized in the monoclinic space group P2(1), with two molecules per asymmetric unit and unit-cell parameters a = 48.58, b = 91.75, c = 89.55 Å, β = 98.29°, and showed diffraction to 2.3 Å resolution.

Structural analysis of alkaline β-mannanase from alkaliphilic Bacillus sp. N16-5: implications for adaptation to alkaline conditions

Significant progress has been made in isolating novel alkaline β-mannanases, however, there is a paucity of information concerning the structural basis for alkaline tolerance displayed by these β-mannanases. We report the catalytic domain structure of an industrially important β-mannanase from the alkaliphilic Bacillus sp. N16-5 (BSP165 MAN) at a resolution of 1.6 Å. This enzyme, classified into subfamily 8 in glycosyl hydrolase family 5 (GH5), has a pH optimum of enzymatic activity at pH 9.5 and folds into a classic (β/α)(8)-barrel. In order to gain insight into molecular features for alkaline adaptation, we compared BSP165 MAN with previously reported GH5 β-mannanases. It was revealed that BSP165 MAN and other subfamily 8 β-mannanases have significantly increased hydrophobic and Arg residues content and decreased polar residues, comparing to β-mannanases of subfamily 7 or 10 in GH5 which display optimum activities at lower pH. Further, extensive structural comparisons show alkaline β-mannanases possess a set of distinctive features. Position and length of some helices, strands and loops of the TIM barrel structures are changed, which contributes, to a certain degree, to the distinctly different shaped (β/α)(8)-barrels, thus affecting the catalytic environment of these enzymes. The number of negatively charged residues is increased on the molecular surface, and fewer polar residues are exposed to the solvent. Two amino acid substitutions in the vicinity of the acid/base catalyst were proposed to be possibly responsible for the variation in pH optimum of these homologous enzymes in subfamily 8 of GH5, identified by sequence homology analysis and pK(a) calculations of the active site residues. Mutational analysis has proved that Gln91 and Glu226 are important for BSP165 MAN to function at high pH. These findings are proposed to be possible factors implicated in the alkaline adaptation of GH5 β-mannanases and will help to further understanding of alkaline adaptation mechanism.

Three endo-β-mannanase genes expressed in the micropylar endosperm and in the radicle influence germination of Arabidopsis thaliana seeds

Mannans are hemicellulosic polysaccharides in the plant primary cell wall (CW). Mature seeds, specially their endosperm cells, have CWs rich in mannan-based polymers that confer a strong mechanical resistance for the radicle protrusion upon germination. The rupture of the seed coat and endosperm are two sequential events during the germination of Arabidopsis thaliana. Endo-β-mannanases (MAN; EC. 3.2.1.78) are hydrolytic enzymes that catalyze cleavage of β1 → 4 bonds in the mannan-polymer. In the genome of Arabidopsis, the endo-β-mannanase (MAN) family is represented by eight members. The expression of these eight MAN genes has been systematically explored in different organs of this plant and only four of them (AtMAN7, AtMAN6, AtMAN2 and AtMAN5) are expressed in the germinating seeds. Moreover, in situ hybridization analysis shows that their transcript accumulation is restricted to the micropylar endosperm and to the radicle and this expression disappears soon after radicle emergence. T-DNA insertion mutants in these genes (K.O. MAN7, K.O. MAN6, K.O. MAN5), except that corresponding to AtMAN2 (K.O. MAN2), germinate later than the wild type (Wt). K.O. MAN6 is the most affected in the germination time course with a t (50) almost double than that of the Wt. These data suggest that AtMAN7, AtMAN5 and specially AtMAN6 are important for the germination of A. thaliana seeds by facilitating the hydrolysis of the mannan-rich endosperm cell walls.

[Identification of the catalytic residues of mannanase from Alicyclobacillus acidocaldarius]

OBJECTIVE

To identify the catalytic residues of mannanase AaManA from Alicyclobacillus acidocaldarius.

METHODS

Based on the sequence alignment by ClustalX and ESPript and the structure information of GH -53 family, the possible catalytic residues were selected and mutated by overlap extension PCR. The protein of wild type and mutant were expressed in E. coli BL21 (DE3) and ordinal purified by Ni - NTA affinity chromatography, gel - filtrate chromatography and ion - exchange chromatography. The purified protein was analyzed by thin layer chromatography (TLC) and the dinitrosalicylic acid (DNS) methods for enzyme assay.

RESULTS

Seven mutants, E151A, E159A, E231A, C150A, E151Q, E231Q and double mutation E151Q&E231Q were successful constructed. Mutant E159A showed similar activities with wild type, and C150A mutation resulted in only a 3 -fold reduction in the activities, but mutations E151A, E231A, E151Q, E231Q and E151Q&E231Q resulted in sharp decreases or loss in the activities, indicating that Glu151 and Glu231 play critical roles in AaManA activity. Furthermore, the presence of Glu151 at the C terminus of beta4 and Glu231 at the C terminus of beta7 was entirely consistent with the positions of the acid/base catalyst and the nucleophile catalyst of a GH - A enzyme, respectively.

CONCLUSION

By combining the results of TLC and enzyme assay of those mutants and the structural comparisons, it was confirmed that Glu151 and Glu231 fulfilled the roles of an acid/base catalyst and nucleophile catalyst in AaManA, respectively.

Cloning and characterization of a novel mannanase from Paenibacillus sp. BME-14

A mannanase gene (man26B) was obtained from a sea bacterium, Paenibacillus sp. BME-14, through the constructed genomic library and inverse PCR. The gene of man26B had an open reading frame of 1,428 bp that encoded a peptide of 475- amino acid residues with a calculated molecular mass of 53 kDa. Man26B possessed two domains, a carbohydrate binding module (CBM) belonging to family 6 and a family 26 catalytic domain (CD) of glycosyl hydrolases, which showed the highest homology to Cel44C of P. polymyxa (60% identity). The optimum pH and temperature for enzymatic activity of Man26B were 4.5 and 60 degrees C, respectively. The activity of Man26B was not affected by Mg(2+) and Co(2+), but was inhibited by Hg(2+), Ca(2+), Cu(2+), Mn(2+), K(+), Na(+), and beta-mercaptoethanol, and slightly enhanced by Pb(2+) and Zn(2+). EDTA did not affect the activity of Man26B, which indicates that it does not require divalent ions to function. Man26B showed a high specific activity for LBG and konjac glucomannan, with K(m), V(max), and k(cat) values of 3.80 mg/ml, 91.70 micromol/min/mg protein, and 77.08/s, respectively, being observed when LBG was the substrate. Furthermore, deletion of the CBM6 domain increased the enzyme stability while enabling it to retain 80% and 60% of its initial activity after treatment at 80 degrees C and 90 degrees C for 30 min, respectively. This finding will be useful in industrial applications of Man26B, because of the harsh circumstances associated with such processes.

Transcriptional regulation and molecular characterization of the manA gene encoding the biofilm dispersing enzyme mannan endo-1,4-beta-mannosidase in Xanthomonas campestris

Exopolysaccharide and several extracellular enzymes of Xanthomonas campestris pv. campestris (Xcc), the causative agent of black rot in crucifers, are important virulence determinants. It is known that Clp (cAMP receptor protein-like protein) and RpfF (an enoyl-CoA hydratase homologue required for the synthesis of diffusible signal factor, DSF) regulate the production of these determinants. Addition of DSF or Xcc extracellular protein containing partially purified mannanase (EC 3.2.1.78, encoded by manA) can disperse the cell aggregates formed by rpfF mutant. In this study, nucleotide G 64 nt upstream of the manA translation start codon was determined as the transcription initiation site by the 5' RACE technique. Transcriptional fusion assays showed that manA transcription is positively regulated by Clp and RpfF and induced by locust bean gum. The manA coding region was cloned and expressed in E. coli as recombinant ManA (rManA). The rManA was purified by affinity chromatography, and its biochemical properties were characterized. The rManA had a pH optimum at 7.0 (0.1 M Hepes) and a temperature optimum at about 37 degrees C. Sequence and mutational analyses demonstrated that Xcc manA encodes the major mannanase, a member of family 5 of glycosyl hydrolases. This study not only extends previous work on Clp and RpfF regulation by showing that they both influence the expression of manA in Xcc, but it also for the first time characterizes Xanthomonas mannanase at the protein level.

[Directed evolution by error-prone PCR of Armillariella tabescens MAN47 beta-mannanase gene toward enhanced thermal resistance]

Firstly, We used error-prone PCR to induce mutations on Armillariella tabescens MAN47 beta-mannanase gene, Secondly, we cloned the mutated fragments into secreted expression vector pYCalpha, Then the recombinant plasmids were transformed into Saccharomyces cerevisiae BJ5465 after amplified and extracted in DH5alpha cells. Through three cycles of error-prone PCR we built a mutant database, Then we screened one optimum (named M262) from about 104 mutants. The evoluted MAN47 beta-mannanase displayed both higher thermal stability and activity than wide type. The evoluted enzyme M262 retained high activity after treatment at 80 degrees C for 30 min, whereas, the wild type nearly lost activity under this condition. Meanwhile, the activity of M262 can reach to 25 U/mL, which is 4.3 times as wide type under optimum temperature. In addition, pH stability and pH range of evoluted enzyme M262 were both improved compared with wild-type enzyme. The optimum pH was estimated to be similar to that of wild-type enzyme. The sequence comparison illustrated that there were three nucleotide substitutions (T343A/C827T/T1139C) which carried corresponding amino acid changes (Ser115Thr/Thr276Met/Val380Ala). According to homologous modeling by SWISS-MODEL Repository, three mutated amino acids located at the sixth amino acid of the fourth beta-sheet, the first amino acid of the sixth alpha-helix, the turn between the tenth and eleventh beta-sheet, respectively.

Purification and characterization of endo-beta-1,4 mannanase from Aspergillus niger gr for application in food processing industry

A thermostable extracellular beta-mannanase from the culture supernatant of a fungus Aspergillus niger gr was purified to homogeneity. SDS-PAGE of the purified enzyme showed a single protein band of molecular mass 66 kDa. The beta- mannanase exhibited optimum catalytic activity at pH 5.5 and 55 degrees C. It was thermostable at 55 degrees C, and retained 50% activity after 6 h at 55 degrees C. The enzyme was stable at a pH range of 3.0 to 7.0. The metal ions Hg(2+), Cu(2+), and Ag(2+) inhibited complete enzyme activity. The inhibitors tested, EDTA, PMSF, and 1,10-phenanthroline, did not inhibit the enzyme activity. N-Bromosuccinimide completely inhibited enzyme activity. The relative substrate specificity of enzyme towards the various mannans is in the order of locust bean gum>guar gum>copra mannan, with K(m) of 0.11, 0.28, and 0.33 mg/ml, respectively. Since the enzyme is active over a wide range of pH and temperature, it could find potential use in the food-processing industry.

[Recent advances and prospect on structural biology of beta-mannanase--a review]

Beta-mannanases (beta-1,4-D-mannanase, EC 3.2.1.78), as a hemicellulose hydrolase, are widely distributed in bacteria, fungi, plants and even animals. They can randomly hydrolyze the beta-1,4-mannosidic linkages in mannan and heteromannan and have great potential in the food/feed, pulp/paper, medicine, oil exploitation and detergent industries. Most beta-mannanases often display a modular organization and usually contain structurally discrete catalytic and non-catalytic modules. Catalytic domains of these enzymes share a (beta/alpha)8-barrel fold, which play important roles in substrate binding and catalysis. Carbohydrate binding modules, as the most common non-catalytic modules, fold as beta-sandwich and facilitate the targeting of these enzymes to polysaccharide. In this review, a brief introduction is given concerning structural characteristics and function of these beta-mannanase modules.

[Cloning, expression and characterization of mannanase from Armillariella tabescens EJLY2098 in Pichia pastoris]

We used reverse transcriptase polymerase chain reaction (RT-PCR) and rapid amplification of cDNA end (RACE) techniques to obtain the full-length cDNA of beta-mannanase (EC 3.2.1.78) from Armillariella tabescens EJLY2098 (an edible fungus). Sequence analysis of the 1481 bp full-length cDNA encoding 445 amino acid residues indicated that the gene contained two structural domains, cellulose-binding domains (CBD) and glycoside hydrolase family 5 (GHF5) domains, other than the conserved beta-mannanase domain. Thus, we classified this gene as a member of glycoside hydrolase family 5. Next, we cloned a 1308 bp fragment encoding the beta-mannanase mature peptide (re-atMAN47) into the expression vector pPICZalphaA and expressed it in Pichia pastoris. The yield was 440 mg/L. Enzyme activity reached a maximum of 1.067 IU/mL after 72 h of methanol induction. The re-atMAN47 had an optimal temperature of 60 degrees C and an optimal pH of 5.5. It manifested broad thermostability from 30 degrees C-65 degrees C, and was stable between pH 4.5-7.0. This study represents the first record of a beta-mannanase from Armillariella tabescens EJLY2098 and provides a new source of carbohydrate hydrolysis enzyme with good biosafety, thermostability and wide pH stability. It is a good approach for the industrial needs of feed, food and pharmaceutical manufacturers.

Transglycosylating and hydrolytic activities of the beta-mannosidase from Trichoderma reesei

A purified beta-mannosidase (EC 3.2.1.25) from the fungus Trichoderma reesei has been identified as a member of glycoside hydrolase family 2 through mass spectrometry analysis of tryptic peptides. In addition to hydrolysis, the enzyme catalyzes substrate transglycosylation with p-nitrophenyl beta-mannopyranoside. Structures of the major and minor products of this reaction were identified by NMR analysis as p-nitrophenyl mannobiosides and p-nitrophenyl mannotriosides containing beta-(1-->4) and beta-(1-->3) linkages. The rate of donor substrate hydrolysis increased in presence of acetonitrile and dimethylformamide, while transglycosylation was weakly suppressed by these organic solvents. Differential ultraviolet spectra of the protein indicate that a rearrangement of the hydrophobic environment of the active site following the addition of the organic solvents may be responsible for this hydrolytic activation.

The Cellvibrio japonicus mannanase CjMan26C displays a unique exo-mode of action that is conferred by subtle changes to the distal region of the active site

The microbial degradation of the plant cell wall is a pivotal biological process that is of increasing industrial significance. One of the major plant structural polysaccharides is mannan, a beta-1,4-linked d-mannose polymer, which is hydrolyzed by endo- and exo-acting mannanases. The mechanisms by which the exo-acting enzymes target the chain ends of mannan and how galactose decorations influence activity are poorly understood. Here we report the crystal structure and biochemical properties of CjMan26C, a Cellvibrio japonicus GH26 mannanase. The exo-acting enzyme releases the disaccharide mannobiose from the nonreducing end of mannan and mannooligosaccharides, harnessing four mannose-binding subsites extending from -2 to +2. The structure of CjMan26C is very similar to that of the endo-acting C. japonicus mannanase CjMan26A. The exo-activity displayed by CjMan26C, however, reflects a subtle change in surface topography in which a four-residue extension of surface loop creates a steric block at the distal glycone -2 subsite. endo-Activity can be introduced into enzyme variants through truncation of an aspartate side chain, a component of a surface loop, or by removing both the aspartate and its flanking residues. The structure of catalytically competent CjMan26C, in complex with a decorated manno-oligosaccharide, reveals a predominantly unhydrolyzed substrate in an approximate (1)S(5) conformation. The complex structure helps to explain how the substrate "side chain" decorations greatly reduce the activity of the enzyme; the galactose side chain at the -1 subsite makes polar interactions with the aglycone mannose, possibly leading to suboptimal binding and impaired leaving group departure. This report reveals how subtle differences in the loops surrounding the active site of a glycoside hydrolase can lead to a change in the mode of action of the enzyme.

Synthesis, Characterization, and Evaluation of Phosphated Cross-Linked Konjac Glucomannan Hydrogels for Colon-Targeted Drug Delivery

Hydrogel systems of konjac glucomannan (KGM) cross-linked with trisodium trimetaphosphate (STMP) were prepared for colon-targeting drug delivery. Swelling degrees of the hydrogels were measured in artificial gastrointestinal fluids and in sodium chloride solution with different concentrations to study their dependence on the cross-linking density and the ionic strength. The absorption of methylene blue was used to characterize the degree of the KGM cross-linking. In vitro release of model drug hydrocortisone was studied in presence and absence of beta -mannanase. KGM cross-linked with STMP was able to retard the release of the poorly water-soluble drug and could be biodegraded enzymatically. Hydrocortisone release was cross-linking density dependent and controlled by degradation of the hydrogles.

Crystallization and preliminary X-ray study of alkaline beta-mannanase from the alkaliphilic Bacillus sp. N16-5

The catalytic domain of an alkaline beta-mannanase from the alkaliphilic Bacillus sp. N16-5 has been expressed and purified. The recombinant enzyme was crystallized using the hanging-drop vapour-diffusion method at 298 K. X-ray diffraction data were collected to 1.6 A resolution. The crystal belonged to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 59.03, b = 63.31, c = 83.34 A. Initial phasing was carried out by molecular replacement using the three-dimensional structure of a mannanase from the alkaliphilic Bacillus sp. JAMB602 as a search model.