Microbial Mannanases: An Overview of Production and Applications

Gene cloning and enzymatic characterization of an alkali-tolerant endo-1,4-β-mannanase from Rhizomucor miehei

An endo-1,4-β-mannanase gene (RmMan5A) was cloned from the thermophilic fungus Rhizomucor miehei for the first time and expressed in Escherichia coli . The gene had an open reading frame of 1330 bp encoding 378 amino acids and contained four introns. It displayed the highest amino acid sequence identity (42%) with the endo-1,4-β-mannanases from glycoside hydrolase family 5. The purified enzyme was a monomer of 43 kDa. RmMan5A displayed maximum activity at 55 °C and an optimal pH of 7.0. It was thermostable up to 55 °C and alkali-tolerant, displaying excellent stability over a broad pH range of 4.0-10.0, when incubated for 30 min without substrate. The enzyme displayed the highest specificity for locust bean gum (K(m) = 3.78 mg mL⁻¹), followed by guar gum (K(m) = 7.75 mg mL⁻¹) and konjac powder (K(m) = 22.7 mg mL⁻¹). RmMan5A hydrolyzed locust bean gum and konjac powder yielding mannobiose, mannotriose, and a mixture of various mannose-linked oligosaccharides. It was confirmed to be a true endo-acting β-1,4-mannanase, which showed requirement of four mannose residues for hydrolysis, and was also capable of catalyzing transglycosylation reactions. These properties make RmMan5A highly useful in the food/feed, paper and pulp, and detergent industries.

Galactoglucomannan extracted from spruce (Picea abies) as a carbohydrate source for probiotic bacteria

A prebiotic is a nonviable food component that confers a health benefit on the host associated with modulation of the microbiota. Hemicelluloses are the second most common group of polysaccharides in nature and they occur in plant cell walls. The predominant hemicellulose in softwood species is galactoglucomannan, and based on its chemical structure and information available about similar saccharides, galactoglucomannan may be postulated to have prebiotic properties. In this study we demonstrated that Bifidobacterium species are able to ferment hemicellulose-derived saccharides. Significant stimulatory effects on the growth rates of bifidobacteria were found when galactoglucomannan or its hydrolysis products were present. Bifidobacterium animalis subsp. lactis strain Bb12, a commonly used probiotic, was able to adapt to the galactoglucomannan leading to more efficient utilization of hemicellulose-derived saccharides. Our study demonstrates prebiotic properties for galactoglucomannan and warrants the next step, that is, characterization of the effects of galactoglucomannan in food.

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.

Binding of bivalent ions to actinomycete mannanase is accompanied by conformational change and is a key factor in its thermal stability

The study aimed to define the key factors involved in the modulation of actinomycete mannanases. We focused on the roles of carbohydrate-binding modules (CBMs) and bivalent ions. To investigate the effects of these factors, two actinomycete mannanase genes were cloned from Streptomyces thermoluteus (StManII) and Streptomyces lividans (SlMan). CBMs fused to mannanase catalytic domains do not affect the thermal stability of the proteins. CBM2 of StManII increased the catalytic efficiency toward soluble-mannan and insoluble-mannan by 25%-36%, and CBM10 of SlMan increased the catalytic efficiency toward soluble-mannan by 40%-50%. Thermal stability of wild-type and mutant enzymes was enhanced by calcium and manganese. Thermal stability of SlMandC was also slightly enhanced by magnesium. These results indicated that bivalent ion-binding site responsible for thermal stability was in the catalytic domains. Thermal stability of mannanase differed in the kinds of bivalent ions. Isothermal titration calorimetry revealed that the catalytic domain of StManII bound bivalent ions with a K(a) of 5.39±0.45×10(3)-7.56±1.47×10(3)M(-1), and the catalytic domain of SlMan bound bivalent ions with a K(a) of 1.06±0.34×10(3)-3.86±0.94×10(3)M(-1). The stoichiometry of these bindings was consistent with one bivalent ion-binding site per molecule of enzyme. Circular dichroism spectrum revealed that the presence of bivalent ions induced changes in the secondary structures of the enzymes. The binding of certain bivalent ion responsible for thermal stability was accompanied by a different conformational change by each bivalent ion. Actinomycete mannanases belong to GHF5 which contained various hemicellulases; therefore, the information obtained from mannanases applies to the other enzymes.

Development of an industrial medium and a novel fed-batch strategy for high-level expression of recombinant β-mananase by Pichia pastoris

An industrial medium, Corn Steep Liquor Powder Dextrose (CSD medium) was developed for constitutive expression of recombinant β-mananase by Pichia pastoris. The β-mananase activity (513 U/mL) with CSD medium was 1.64- and 2.5-fold higher than with YPD and BSM in shaken flasks. The β-mananase productivity with CSD medium was 61.0 U/mL h, which was 1.7- and 2.5-fold higher than with YPD and BSM in a 5-L fermenter based on a novel fed-batch strategy combining the real-time exponential feed mode with the DO-stat feed mode. The β-mananase activity, dry cell weight and the recombinant enzyme reached up to 5132 U/mL, 110.0 g/L and 4.50 g/L after 50 h cultivation in a 50-L fermenter. The high efficient expression of recombinant β-mananase by P. pastoris indicated that CSD medium and the novel fed-batch strategy have great potential for the production of recombinant β-mananase in industrial fermentation.

Characterization of mannanase from a novel mannanase-producing bacterium

Locust bean gum (LBG) was employed to screen mannanase-producing bacteria. The bacterium with highest mannanase ability was identified as Paenibacillus cookii. It revealed highest activity (6.67 U/mL) when cultivated in 0.1% LBG with 1.5% soytone and 0.5% tryptone after 4 days incubation at 27 °C. Its mannanase was purified to electrophoretical homogeneity after DEAE-Sepharose and Sephacryl S-100 separation. The purified mannanase, with an N-terminus of GLFGINAY, had pH and temperature optimum at 5.0 and 50 °C, respectively, and was stable at pH 5.0-7.0, ≤ 50 °C. It was strongly activated by β-mercaptoethanol, dithiothreitol, cysteine, and glutathione, but inhibited by Hg(2+), Cu(2+), Zn(2+), Fe(3+), PMSF, iodoacetic acid, and EDTA. According to substrate specificity study, the purified mannanase had high specificity to LBG and konjac.

Softening-up mannan-rich cell walls

The softening and degradation of the cell wall (CW), often mannan enriched, is involved in several processes during development of higher plants, such as meristematic growth, fruit ripening, programmed cell death, and endosperm rupture upon germination. Mannans are also the predominant hemicellulosic CW polymers in many genera of green algae. The endosperm CWs of dry seeds often contain mannan polymers, sometimes in the form of galactomannans (Gal-mannans). The endo-β-mannanases (MANs) that catalyse the random hydrolysis of the β-linkage in the mannan backbone are one of the main hydrolytic enzymes involved in the loosening and remodelling of CWs. In germinating seeds, the softening of the endosperm seed CWs facilitates the emergence of the elongating radicle. Hydrolysis and mobilization of endosperm Gal-mannans by MANs also provides a source of nutrients for early seedling growth, since Gal-mannan, besides its structural role, serves as a storage polysaccharide. Therefore, the role of mannans and of their hydrolytic enzymes is decisive in the life cycle of seeds. This review updates and discusses the significance of mannans and MANs in seeds and explores the increasing biotechnological potential of MAN enzymes.

Gene cloning, expression, and biochemical characterization of an alkali-tolerant β-mannanase from Humicola insolens Y1

In this article, we firstly report a highly alkali-tolerant fungal β-mannanase from Humicola insolens Y1. The full-length cDNA of the β-mannanase, designated as man5A, has an open reading frame of 1,233 bp that encodes a 411-amino acid polypeptide (Man5A) with a calculated molecular mass of 42.3 kDa. The deduced sequence of Man5A comprises a putative 20-residue signal peptide and a catalytic domain belonging to glycoside hydrolase family 5, and displays 61–85% identities with hypothetical proteins and 32–39% with experimentally verified fungal β-mannanases. Purified recombinant Man5A produced by Pichia pastoris has a specific activity of 1,122 U mg−1 and exhibits optimal activity at pH 5.5 and 70°C. Distinct from other reported fungal β-mannanases, Man5A is highly alkali tolerant, exhibiting 45 and 36% of the maximal activity at pH 8.0 and 9.0, respectively, and more than 10% activity even at pH 10.0. Moreover, Man5A has excellent pH stability at pH 5.0–12.0 and is highly thermostable at 50°C. The higher frequency of alkaline amino acids (Arg and Lys), greater pKa values of the catalytic residues, and more positively charged residues on the surface of Man5A might be the causes. Man5A has strong resistance to various neutral and alkaline proteases, retaining more than 97% of the activity after proteolytic treatment for 1 h. The superior characteristics of Man5A make it more advantageous for the application in the kraft pulp industry.

Expression of Trichoderma reesei β-mannanase in tobacco chloroplasts and its utilization in lignocellulosic woody biomass hydrolysis

Lignocellulosic ethanol offers a promising alternative to conventional fossil fuels. One among the major limitations in the lignocellulosic biomass hydrolysis is unavailability of efficient and environmentally biomass degrading technologies. Plant-based production of these enzymes on large scale offers a cost-effective solution. Cellulases, hemicellulases including mannanases and other accessory enzymes are required for conversion of lignocellulosic biomass into fermentable sugars. β-mannanase catalyzes endo-hydrolysis of the mannan backbone, a major constituent of woody biomass. In this study, the man1 gene encoding β-mannanase was isolated from Trichoderma reesei and expressed via the chloroplast genome. PCR and Southern hybridization analysis confirmed site-specific transgene integration into the tobacco chloroplast genomes and homoplasmy. Transplastomic plants were fertile and set viable seeds. Germination of seeds in the selection medium showed inheritance of transgenes into the progeny without any Mendelian segregation. Expression of endo-β-mannanase for the first time in plants facilitated its characterization for use in enhanced lignocellulosic biomass hydrolysis. Gel diffusion assay for endo-β-mannanase showed the zone of clearance confirming functionality of chloroplast-derived mannanase. Endo-β-mannanase expression levels reached up to 25 units per gram of leaf (fresh weight). Chloroplast-derived mannanase had higher temperature stability (40 °C to 70 °C) and wider pH optima (pH 3.0 to 7.0) than E.coli enzyme extracts. Plant crude extracts showed 6-7 fold higher enzyme activity than E.coli extracts due to the formation of disulfide bonds in chloroplasts, thereby facilitating their direct utilization in enzyme cocktails without any purification. Chloroplast-derived mannanase when added to the enzyme cocktail containing a combination of different plant-derived enzymes yielded 20% more glucose equivalents from pinewood than the cocktail without mannanase. Our results demonstrate that chloroplast-derived mannanase is an important component of enzymatic cocktail for woody biomass hydrolysis and should provide a cost-effective solution for its diverse applications in the biofuel, paper, oil, pharmaceutical, coffee and detergent industries.

Acidic β-mannanase from Penicillium pinophilum C1: Cloning, characterization and assessment of its potential for animal feed application

The β-mannanase gene, man5C1, was cloned from Penicillium pinophilum C1, a strain isolated from the acidic wastewater of a tin mine in Yunnan, China, and expressed in Pichia pastoris. The sequence analysis displayed the gene consists of a 1221-bp open reading frame encoding a protein of 406 amino acids (Man5C1). The deduced amino acid sequence of Man5C1 showed the highest homology of 57.8% (identity) with a characterized β-mannanase from Aspergillus aculeatus belonging to glycoside hydrolase family 5. The purified rMan5C1 had a high specific activity of 1035U mg(-1) towards locust bean gum (LBG) and showed highest activity at pH 4.0 and 70°C. rMan5C1 was adaptable to a wide range of acidity, retaining >60% of its maximum activity at pH 3.0-7.0. The enzyme was stable over a broad pH range (3.0 to 10.0) and exhibited good thermostability at 50°C. The K(m) and V(max) values were 5.6 and 4.8mgmL(-1), and 2785 and 1608μmolmin(-1)mg(-1), respectively, when LBG and konjac flour were used as substrates. The enzyme had strong resistance to most metal ions and proteases (pepsin and trypsin), and released 8.96mgg(-1) reducing sugars from LBG in the simulated gastric fluid. All these favorable properties make rMan5C1 a promising candidate for use in animal feed.

Improved Mannanase Production from Penicillium occitanis by Fed-Batch Fermentation Using Acacia Seeds

By applying a fed-batch strategy, production of Penicillium occitanis mannanases could be almost doubled as compared to a batch cultivation on acacia seeds (76 versus 41 U/mL). Also, a 10-fold increase of enzyme activities was observed from shake flask fermentation to the fed-batch fermentation. These production levels were 3-fold higher than those obtained on coconut meal. The high mannanase production using acacia seeds powder as inducer substrate showed the suitability of this culture process for industrial-scale development.

Recombinant production and characterisation of two related GH5 endo-β-1,4-mannanases from Aspergillus nidulans FGSC A4 showing distinctly different transglycosylation capacity

The glycoside hydrolase family 5 (GH5) endo-β-1,4-mannanases ManA and ManC from Aspergillus nidulans FGSC A4 were produced in Pichia pastoris X33 and purified in high yields of 120 and 145mg/L, respectively, from the culture supernatants. Both enzymes showed increasing catalytic efficiency (k(cat)/K(M)) towards β-1,4 manno-oligosaccharides with the degree of polymerisation (DP) from 4 to 6 and also hydrolysed konjac glucomannan, guar gum and locust bean gum galactomannans. ManC had up to two-fold higher catalytic efficiency for DP 5 and 6 manno-oligosaccharides and also higher activity than ManA towards mannans. Remarkably, ManC compared to ManA transglycosylated mannotetraose with formation of longer β-1,4 manno-oligosaccharides 8-fold more efficiently and was able to use mannotriose, melezitose and isomaltotriose out of 36 tested acceptors resulting in novel penta- and hexasaccharides, whereas ManA used only mannotriose as acceptor. ManA and ManC share 39% sequence identity and homology modelling suggesting that they have very similar substrate interactions at subsites +1 and +2 except that ManC Trp283 at subsite +1 corresponded to Ser289 in ManA. Site-directed mutagenesis to ManA S289W lowered K(M) for manno-oligosaccharides by 30-45% and increased transglycosylation yield by 50% compared to wild-type. Conversely, K(M) for ManC W283S was increased, the transglycosylation yield was reduced by 30-45% and furthermore activity towards mannans decreased below that of ManA. This first mutational analysis in subsite +1 of GH5 endo-β-1,4-mannanases indicated that Trp283 in ManC participates in discriminating between mannan substrates with different extent of branching and has a role in transglycosylation and substrate affinity.

A thermotolerant and cold-active mannan endo-1,4-β-mannosidase from Aspergillus niger CBS 513.88: Constitutive overexpression and high-density fermentation in Pichia pastoris

The mannan endo-1,4-β-mannosidase gene man26A from Aspergillus niger CBS 513.88 was optimized according to the codon usage bias in Pichia pastoris and synthesized by splicing overlap extension PCR. It was successfully expressed in P. pastoris using constitutive expression vector pGAPzαA. The recombinant endo-beta-1,4-mannanase could work in an extremely board temperature range and over 30% relative activity were retained in the temperature range of 5-60°C. The optimal pH value and temperature for activity were 5.0 and 45°C, respectively. It was highly thermotolerant with a half-life time of 15min at 90°C. A novel fed-batch strategy was developed successfully for high cell-density fermentation and mannanase activity reached 5069U/mL after cultivation for 56h in 50L fermenter. The broad working temperature range, high thermotolerance and efficient expression made this enzyme possible to be applied in food, animal feed and the production of biofuels.

Combinatorial strategy of sorbitol feeding and low-temperature induction leads to high-level production of alkaline β-mannanase in Pichia pastoris

A process for efficient production of an alkaline β-mannanases from Bacillus sp. N16-5 was established by heterologous expression using Pichia pastoris. A high producing strain was generated by removing the native β-mannanases signal peptide and increasing the copy number of the mature β-mannanases gene. High cell density fermentation of this strain in 1-L bioreactor led to a production level of 4164 U/mL after 96 h of induction. Sorbitol co-feeding and temperature-lowering strategies both increased the β-mannanase production levels. Combined usage of these two strategies achieved the most effective result-the enzyme level reached 6336 U/mL within 84 h, which to our best knowledge is the highest production level reported for the expression of extreme β-mannanase thus far. The strategy described in this work can also be adapted to express other important industrial enzymes with extreme properties.

cDNA cloning and bacterial expression of an endo-β-1,4-mannanase, AkMan, from Aplysia kurodai

Previously we isolated an endo-β-1,4-mannanase (EC 3.2.1.78), AkMan, from the digestive fluid of a common sea hare Aplysia kurodai and demonstrated that this enzyme had a broad pH optimum spanning 4.0 to 7.5 and an appreciably high heat stability in this pH range (Zahura et al., Comp. Biochem. Physiol., B157, 137-148 (2010)). In the present study, we cloned the cDNA encoding AkMan and constructed a bacterial expression system for this enzyme to enrich information about the primary structure and the characteristic properties of this enzyme. cDNA fragments encoding AkMan were amplified by PCR followed by 5'- and 3'-RACE PCRs from the A. kurodai hepatopancreas cDNA using degenerated primers designed on the basis of partial amino-acid sequences of AkMan. The cDNA including entire translational region of AkMan consisted of 1392bp and encoded 369 amino-acid residues. The N-terminal region of 17 residues of the deduced sequence except for the initiation Met was regarded as the signal peptide of AkMan and the mature enzyme region was considered to comprise 351 residues with a calculated molecular mass of 39961.96Da. Comparison of the primary structure of AkMan with other β-1,4-mannanases indicated that AkMan belongs to the subfamily 10 of glycosyl-hydrolase-family-5 (GHF5). Phylogenetic analysis for the GHF5 β-1,4-mannanases indicated that AkMan together with other molluscan β-1,4-mannanases formed an independent clade of the subfamily 10 in the phylogenetic tree. The recombinant AkMan (recAkMan) was expressed with an Escherichia coli BL21(DE3)-pCold1 expression system as an N-terminal hexahistidine-tagged protein and purified by Ni-NTA affinity chromatography. The recAkMan showed the broad pH optimum in acidic pH range as did native AkMan; however, heat stability of recAkMan was considerably lower than that of native enzyme. This may indicate that the stability of AkMan is derived from an appropriate folding and/or some posttranslational modifications in Aplysia cells.

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.

BOARD-INVITED REVIEW: opportunities and challenges in using exogenous enzymes to improve nonruminant animal production

Diets fed to nonruminant animals are composed mainly of feed ingredients of plant origin. A variety of antinutritional factors such as phytin, nonstarch polysaccharides, and protease inhibitors may be present in these feed ingredients, which could limit nutrients that may be utilized by animals fed such diets. The primary nutrient utilization-limiting effect of phytin arises from the binding of 6 phosphate groups, thus making the P unavailable to the animal. The negative charges allow for formation of insoluble phytin-metal complexes with many divalent cations. Furthermore, phytin and protein can form binary complexes through electrostatic links of its charged phosphate groups with either the free amino group on AA on proteins or via formation of ternary complexes of phytin, Ca(2+), and protein. The form and extent of de novo formation of binary and ternary complexes of phytin and protein are likely to be important variables that influence the effectiveness of nutrient hydrolysis in plant-based diets. Nonstarch polysacharides reduce effective energy and nutrient utilization by nonruminant animals because of a lack of the enzymes needed for breaking down the complex cell wall structure that encapsulate other nutrients. Enzymes are used in nonruminant animal production to promote growth and efficiency of nutrient utilization and reduce nutrient excretion. The enzymes used include those that target phytin and nonstarch polysaccharides. Phytase improves growth and enhances P utilization, but positive effects on other nutrients are not always observed. Nonstarch polysaccharide-hydrolyzing enzymes are less consistent in their effects on growth and nutrient utilization, although they show promise and it is imperative to closely match both types and amounts of nonstarch polysaccharides with appropriate enzyme for beneficial effects. When used together with phytase, nonstarch polysaccharide-hydrolyzing enzymes may increase the accessibility of phytase to phytin encapsulated in cell walls. The future of enzymes in nonruminant animal production is promising and will likely include an understanding of the role of enzyme supplementation in promoting health as well as how enzymes may modulate gene functions. This review is an attempt to summarize current thinking in this area, provide some clarity in nomenclature and mechanisms, and suggest opportunities for expanded exploitation of this unique biotechnology.

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.

Cloning, expression, purification, crystallization and preliminary X-ray diffraction studies of the catalytic domain of a hyperthermostable endo-1,4-beta-D-mannanase from Thermotoga petrophila RKU-1

Endo-1,4-beta-D-mannanases play key roles in seed germination and fruit ripening and have recently received much attention owing to their potential applications in the food, detergent and kraft pulp industries. In order to delineate their structural determinants for specificity and stability, X-ray crystallographic investigations combined with detailed functional studies are being performed. In this work, crystals of the catalytic domain of a hyperthermostable endo-1,4-beta-D-mannanase from Thermotoga petrophila RKU-1 were obtained from three different conditions, resulting in two crystalline forms. Crystals from conditions with phosphate or citrate salts as precipitant (CryP) belonged to space group P2(1)2(1)2(1), with unit-cell parameters a=58.76, b=87.99, c=97.34 A, while a crystal from a condition with ethanol as precipitant (CryE) belonged to space group I2(1)2(1)2(1), with unit-cell parameters a=91.03, b=89.97, c=97.89 A. CryP and CryE diffracted to resolutions of 1.40 and 1.45 A, respectively.

Genetic and biochemical characterization of a protease-resistant mesophilic β-mannanase from Streptomyces sp. S27

A β-mannanase gene, designated as man5S27, was cloned from Streptomyces sp. S27 using the colony polymerase chain reaction (PCR) method and expressed in Escherichia coli BL21 (DE3). The open reading frame consisted of 1,161 bp and encoded a 386-amino-acid polypeptide (Man5S27) with calculated molecular mass of 37.2 kDa. The encoded protein comprised a putative 38-residue signal peptide, a family 5 glycoside hydrolase domain, and a family 10 carbohydrate-binding module. Purified recombinant Man5S27 had high specific activity of 2,107 U mg⁻¹ and showed optimal activity at pH 7.0 and 65 °C. The enzyme remained stable at pH 5.0-9.0 and had good thermostability at 50°C. The K (m) values for locust bean gum and konjac flour were 0.16 and 0.41 mg ml⁻¹, with V(max) values of 3,739 and 1,653 μmol min⁻¹ mg⁻¹, respectively. Divalent metal ions such as Mn²+, Zn²+, Ca²+, Pb²+, and Fe²+ enhanced the enzyme activity, but Ag+ and Hg²+ strongly inhibited the activity. Man5S27 also showed resistance to various neutral proteases (retaining >95% activity after proteolytic treatment for 2 h).

Redesign the α/β fold to enhance the stability of mannanase Man23 from Bacillus subtilis

In this work, we engineered the α/β fold of mannanase Man23 based on its molecular structure analysis to obtain more stable variants. By introducing 31 single-site mutations in the α/β fold and shuffling them, the incorporation of four mutations (K178R, K207R, N340R, and S354R) displayed a good balance between high activity and stability at higher temperature and broader pH. This quartet variant was characterized by an almost threefold increased activity and a sevenfold increased stability compared to native mannanase Man23. Our results suggest that such work is safe to increase our target protein stability with no loss of activity.