An Aspergillus nidulans β-mannanase with high transglycosylation capacity revealed through comparative studies within glycosidase family 5

Biochemical analyses of a novel acidophilic GH5 β-mannanase from Trichoderma asperellum ND-1 and its application in mannooligosaccharides production from galactomannans

In this study, an acidophilic GH5 β-mannanase (TaMan5) from Trichoderma asperellum ND-1 was efficiently expressed in Pichia pastoris (a 2.0-fold increase, 67.5 ± 1.95 U/mL). TaMan5 displayed the highest specificity toward locust bean gum (K_m = 1.34 mg/mL, V_max = 749.14 μmol/min/mg) at pH 4.0 and 65°C. Furthermore, TaMan5 displayed remarkable tolerance to acidic environments, retaining over 80% of its original activity at pH 3.0-5.0. The activity of TaMan5 was remarkably decreased by Cu²⁺, Mn²⁺, and SDS, while Fe²⁺/Fe³⁺ improved the enzyme activity. A thin-layer chromatography (TLC) analysis of the action model showed that TaMan5 could rapidly degrade mannan/MOS into mannobiose without mannose via hydrolysis action as well as transglycosylation. Site-directed mutagenesis results suggested that Glu²⁰⁵, Glu³¹³, and Asp³⁵⁷ of TaMan5 are crucial catalytic residues, with Asp¹⁵² playing an auxiliary function. Additionally, TaMan5 and commercial α-galactosidase displayed a remarkable synergistic effect on the degradation of galactomannans. This study provided a novel β-mannanase with ideal characteristics and can be considered a potential candidate for the production of bioactive polysaccharide mannobiose.

Thermotolerant and protease-resistant GH5 family β-mannanase with CBM1 from Penicillium aculeatum APS1: purification and characterization

In past several years, mannanases has attracted many researchers owing to its extensive industrial applications. The search for novel mannanases with high stability still continues. Present investigation was focused on purification of extracellular β-mannanase from Penicillium aculeatum APS1 and its characterization. APS1 mannanase was purified to homogeneity by chromatography techniques. Protein identification by MALDI-TOF MS/MS revealed that the enzyme belongs to GH family 5 and subfamily 7, and possesses CBM1. The molecular weight was found to be 40.6 kDa. The optimum temperature and pH of APS1 mannanase were 70 °C and 5.5, respectively. APS1 mannanase was found to be highly stable at 50 °C and tolerant at 55-60 °C. The enzyme was very sensitive to Mn+2, Hg+2 and Co+2 metal ions and stimulated by Zn+2. Inhibition of activity by N-bromosuccinimide suggested key role of tryptophan residues for catalytic activity. The purified enzyme was efficient in hydrolysis of locust bean gum, guar gum and konjac gum and kinetic studies revealed highest affinity towards locust bean gum (LBG). APS1 mannanase was found to be protease resistant. Looking at the properties, APS1 mannanase can be a valuable candidate for applications in bioconversion of mannan-rich substrates into value-added products and also in food and feed processing.

Molecular insight into Aspergillus oryzae β-mannanase interacting with mannotriose revealed by molecular dynamic simulation study

Fungal β-mannanases hydrolyze β-1, 4-glycosidic bonds of mannans and find application in the generation of mannose and prebiotic mannooligosaccharides (MOS). Previously, a MOS generating β-mannanase from Aspergillus oryzae MTCC 1846 (βManAo) was characterized and its structural and functional properties were unraveled through homology modeling and molecular dynamics in this study. The βManAo model was validated with 92.9% and 6.5% of the residues found to be distributed in the most favorable and allowed regions of the Ramachandran plot. Glu244 was found to play a key role in the interaction with mannotriose, indicating conserved amino acids for the catalytic reaction. A detailed metadynamic analysis of the principal components revealed the presence of an α₈-helix in the C-terminus which was very flexible in nature and energy landscapes suggested high conformation sub-states and the complex dynamic behavior of the protein. The binding of the M3 substrate stabilized the β-mannanase and resulted in a reduction in the intermediate conformational sub-states evident from the free energy landscapes. The active site of the β-mannanase is mostly hydrophilic in nature which is accordance with our results, where the major contribution in the binding energy of the substrate with the active site is from electrostatic interactions. Define Secondary Structure of Proteins (DSSP) analysis revealed a major transition of the protein from helix to β-turn for binding with the mannotriose. The molecular dynamics of the βManAo–mannotriose model, and the role and interactions of catalytic residues with ligand were also described. The substrate binding pocket of βManAo was found to be highly dynamic and showed large, concerted movements. The outcomes of the present study can be exploited in further understanding the structural properties and functional dynamics of βManAo.

A Single Hydrogen Bond Controls the Selectivity of Transglycosylation vs Hydrolysis in Family 13 Glycoside Hydrolases

Converting glycoside hydrolases (GHs) from hydrolytic to synthetic enzymes via transglycosylation is a long-standing goal for the biosynthesis of complex carbohydrates. However, the molecular determinants for the selectivity of transglycosylation (T) vs hydrolysis (H) are still not fully unraveled. Herein, we show experimentally that mutation of one active site residue can switch the enzyme activity between hydrolysis and transglycosylation in two highly homologous GHs. Further QM/MM simulations reveal that the mutation modulates the T vs H reaction barriers via the presence/absence of a single H-bond with the nucleophile Asp. Such a H-bond controls the product selectivity via a dual effect: on one hand, it facilitates the breaking of the glycosyl-enzyme intermediate. On the other, it displaces the sugar acceptor, resulting in a reduced affinity and significant steric repulsion for transglycosylation. These findings expand our understanding of the molecular mechanisms that modulate the T/H balance in GHs.

A Comparison of the Transglycosylation Capacity between the Guar GH27 Aga27A and Bacteroides GH36 BoGal36A α-Galactosidases

The transglycosylation behavior and capacity of two clan GH-D α-galactosidases, BoGal36A from the gut bacterium Bacteroides ovatus and Aga27A from the guar plant, was investigated and compared. The enzymes were screened for the ability to use para-nitrophenyl-α-galactoside (pNP-Gal), raffinose and locust bean gum (LBG) galactomannan as glycosyl donors with the glycosyl acceptors methanol, propanol, allyl alcohol, propargyl alcohol and glycerol using mass spectrometry. Aga27A was, in general, more stable in the presence of the acceptors. HPLC analysis was developed and used as a second screening method for reactions using raffinose or LBG as a donor substrate with methanol, propanol and glycerol as acceptors. Time-resolved reactions were set up with raffinose and methanol as the donor and acceptor, respectively, in order to develop an insight into the basic transglycosylation properties, including the ratio between the rate of transglycosylation (methyl galactoside synthesis) and rate of hydrolysis. BoGal36A had a somewhat higher ratio (0.99 compared to 0.71 for Aga27A) at early time points but was indicated to be more prone to secondary (product) hydrolysis in prolonged incubations. The methyl galactoside yield was higher when using raffinose (48% for BoGal36A and 38% for Aga27A) compared to LBG (27% for BoGal36A and 30% for Aga27A).

Biochemical and structural characterization of a novel thermophilic and acidophilic β-mannanase from Aspergillus calidoustus

β-Mannanases hydrolyze lignocellulosic biomass with the release of mannan oligosaccharides, which are considered as renewable resource in higher plants. Here, we cloned, expressed and characterized a novel endo-β-mannanase (ManAC) from Aspergillus calidoustus. Homology alignment analysis indicated that ManAC belonged to glycosyl hydrolase (GH) 5 family members. The analysis of structural homologous model revealed that five residues, Arg¹¹⁶, Asn²³¹, His³⁰⁵, Tyr³⁰⁷, and Trp³⁷⁰, constituted the active site of ManAC. Glu²³² and Glu³⁴⁰, proton donor and nucleophile, formed the catalytic residues of ManAC. The recombinant ManAC exhibited maximal activity at pH 2.5 and 70 °C, and it was acid tolerant at a pH range of 2.0-6.0 and thermostable under 60 °C. Meanwhile, the activity of ManAC was not significantly affected by various metal ions, except for Mg²⁺ and Ag²⁺. The recombinant ManAC exhibited the highest β-mannanase activity towards locust bean gum (669.7 U/mg) with the K_m and V_max values of 3.4 mg/mL and 982.4 μmol/min/mg, respectively. These thermophilic and acidophilicc characteristics is better than most extreme β-mannanase. As the first reported mannanse from Aspergillus calidoustus (ManAC), these excellent properties of ManAC strongly promote the synthesis of mannooligosaccharides which have potential for food and feed industrial applications.

Synthesis of α-l-Araf and β-d-Galf series furanobiosides using mutants of a GH51 α-l-arabinofuranosidase

The GH-51 α-l-arabinofuranosidase from Thermobacillus xylanilyticus (TxAbf) possesses versatile catalytic properties, displaying not only the ability to hydrolyze glycosidic linkages but also to synthesize furanobiosides in α-l-Araf and β-d-Galf series. Herein, mutants are investigated to evaluate their ability to perform self-condensation, assessing both yield improvements and changes in regioselectivity. Overall yields of oligo-α-l-arabino- and oligo-β-d-galactofuranosides were increased up to 4.8-fold compared to the wild-type enzyme. In depth characterization revealed that the mutants exhibit increased transfer rates and thus a hydrolysis/self-condensation ratio in favor of synthesis. The consequence of the substitution N216W is the creation of an additional binding subsite that provides the basis for an alternative acceptor substrate binding mode. As a result, mutants bearing N216W synthesize not only (1,2)-linked furanobiosides, but also (1,3)- and even (1,5)-linked furanobiosides. Since the self-condensation is under kinetic control, the yield of homo-disaccharides was maximized using higher substrate concentrations. In this way, the mutant R69H-N216W produced oligo-β-d-galactofuranosides in > 70% yield. Overall, this study further demonstrates the potential usefulness of TxAbf mutants for glycosynthesis and shows how these might be used to synthesize biologically-relevant glycoconjugates.

Crystal structure of a homotrimeric verrucomicrobial exo-β-1,4-mannosidase active in the hindgut of the wood-feeding termite Reticulitermes flavipes

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First structure of a glycoside hydrolase from a bacterial symbiont isolated from the digestive tract of the notorious termite pest Reticulitermes flavipes.

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First example of a GH5 glycoside hydrolase that features a GH42-type homotrimeric structure.

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High exo-type specificity for the terminal ®-1,4-mannosidic linkages in mannooligosaccharides and unsubstituted®-mannans.

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Verrucomicrobial gut symbiont with high potential for hemicellulose degradation.

The termite Reticulitermes flavipes causes extensive damage due to the high efficiency and broad specificity of the ligno- and hemicellulolytic enzyme systems produced by its symbionts. Thus, the R. flavipes gut microbiome is expected to constitute an excellent source of enzymes that can be used for the degradation and valorization of plant biomass. The symbiont Opitutaceae bacterium strain TAV5 belongs to the phylum Verrucomicrobia and thrives in the hindgut of R. flavipes. The sequence of the gene with the locus tag opit5_10225 in the Opitutaceae bacterium strain TAV5 genome has been classified as a member of glycoside hydrolase family 5 (GH5), and provisionally annotated as an endo-β-mannanase. We characterized biochemically and structurally the opit5_10225 gene product, and show that the enzyme, Op5Man5, is an exo-β-1,4-mannosidase [EC 3.2.1.25] that is highly specific for β-1,4-mannosidic bonds in mannooligosaccharides and ivory nut mannan. The structure of Op5Man5 was phased using electron cryo-microscopy and further determined and refined at 2.2 Å resolution using X-ray crystallography. Op5Man5 features a 200-kDa large homotrimer composed of three modular monomers. Despite insignificant sequence similarity, the structure of the monomer, and homotrimeric assembly are similar to that of the GH42-family β-galactosidases and the GH164-family exo-β-1,4-mannosidase Bs164 from Bacteroides salyersiae. To the best of our knowledge Op5Man5 is the first structure of a glycoside hydrolase from a bacterial symbiont isolated from the R. flavipes digestive tract, as well as the first example of a GH5 glycoside hydrolase with a GH42 β-galactosidase-type homotrimeric structure.

Probing the determinants of the transglycosylation/hydrolysis partition in a retaining α-l-arabinofuranosidase

The use of retaining glycoside hydrolases as synthetic tools for glycochemistry is highly topical and the focus of considerable research. However, due to the incomplete identification of the molecular determinants of the transglycosylation/hydrolysis partition (t/h), rational engineering of retaining glycoside hydrolases to create transglycosylases remains challenging. Therefore, to understand better the factors that underpin transglycosylation in a GH51 retaining α-l-arabinofuranosidase from Thermobacillus xylanilyticus, the investigation of this enzyme's active site was pursued. Specifically, the properties of two mutants, F26L and L352M, located in the vicinity of the active site are described, using kinetic and 3D structural analyses and molecular dynamics simulations. The results reveal that the presence of L352M in the context of a triple mutant (also containing R69H and N216W) generates changes both in the donor and acceptor subsites, the latter being the result of a domino-like effect. Overall, the mutant R69H-N216W-L352M displays excellent transglycosylation activity (70 % yield, 78 % transfer rate and reduced secondary hydrolysis of the product). In the course of this study, the central role played by the conserved R69 residue was also reaffirmed. The mutation R69H affects both the catalytic nucleophile and the acid/base, including their flexibility, and has a determinant effect on the t/h partition. Finally, the results reveal that increased loop flexibility in the acceptor subsites creates new interactions with the acceptor, in particular with a hydrophobic binding platform composed of N216W, W248 and W302.

Prebiotic mannooligosaccharides: Synthesis, characterization and bioactive properties

Functional oligosaccharides are non-digestible food ingredients that confer numerous health benefits. Among these, mannooligosaccharides (MOS) are emerging prebiotics that have characteristic potential bio-active properties. Microbial mannanases can be used to break down mannan rich agro-residues to yield MOS. Various applications of MOS as health promoting functional food ingredient may open up newer opportunities in food and feed industry. Enzymatic hydrolysis is the widely preferred method over chemical hydrolysis for MOS production. Presently, commercial MOS is being derived from yeast cell wall mannan and is widely used as prebiotic in feed supplements for poultry and aquaculture. Apart from stimulating the growth of probiotic microflora, MOS impart anticancer and immunomodulatory effects by inducing different gene markers in colon cells. This review summarizes recent developments and future prospects of enzymatic synthesis of MOS from various mannans, their structural characteristics and their potential health benefits.

In vitro and in vivo characterization of genes involved in mannan degradation in Neurospora crassa

To better understand the roles of genes involved in mannan degradation in filamentous fungi, in this study we searched, identified, and characterized one putative GH5 endo-β-mannanase (GH5-7) and two putative GH2 mannan-degrading enzymes (GH2-1 and GH2-4) in Neurospora crassa. Real-time RT-PCR analyses showed that the expression levels of these genes were significantly up-regulated when the cells were grown in mannan-containing media where the induction level of gh5-7 was the highest. All three proteins were heterologously expressed and purified. GH5-7 displayed a substrate preference toward galactomannan by showing 10-times higher catalytic efficiency than to linear β-mannan. In contrast, GH2-1 preferred short manno-oligosaccharides or β-mannan as substrates. Compared to the wild type strain, the growth of Δgh5-7 and Δgh5-7Δgh2-4 mutants, but not Δgh2-1, Δgh2-4, and Δgh2-1Δgh2-4 mutants, was poor in the cultures containing glucomannan or galactomannan as the sole carbon source, suggesting that GH5-7 plays a critical role in the utilization of heteromannans in vivo. On the other hand, all the mutants showed significantly slow growth when grown in the medium containing linear β-mannan. Collectively, these results indicate that N. crassa can utilize glucomannan and galactomannan without GH2-1 and GH2-4, but efficient degradation of β-mannan requires a concerted action of three enzymes, GH5-7, GH2-1, and GH2-4.

A novel strategy for efficient disaccharides synthesis from glucose by β-glucosidase

Oligosaccharides have important therapeutic applications. A useful route for oligosaccharides synthesis is reverse hydrolysis by β-glucosidase. However, the low conversion efficiency of disaccharides from monosaccharides limits its large-scale production because the equilibrium is biased in the direction of hydrolysis. Based on the analysis of the docking results, we hypothesized that the hydropathy index of key amino acid residues in the catalytic site is closely related with disaccharide synthesis and more hydrophilic residues located in the catalytic site would enhance reverse hydrolysis activity. In this study, positive variants TrCel1bI177S, TrCel1bI177S/I174S, and TrCel1bI177S/I174S/W173H, and one negative variant TrCel1bN240I were designed according to the Hydropathy Index For Enzyme Activity (HIFEA) strategy. The reverse hydrolysis with TrCel1bI177S/I174S/W173H was accelerated and then the maximum total production (195.8 mg/mL/mg enzyme) of the synthesized disaccharides was increased by 3.5-fold compared to that of wild type. On the contrary, TrCel1bN240I lost reverse hydrolysis activity. The results demonstrate that the average hydropathy index of the key amino acid residues in the catalytic site of TrCel1b is an important factor for the synthesis of laminaribiose, sophorose, and cellobiose. The HIFEA strategy provides a new perspective for the rational design of β-glucosidases used for the synthesis of oligosaccharides.

High-level expression of a thermophilic and acidophilic β-mannanase from Aspergillus kawachii IFO 4308 with significant potential in mannooligosaccharide preparation

An engineered thermophilic and acidophilic β-mannanase (ManAK) from Aspergillus kawachii IFO 4308 was highly expressed in Pichia pastoris. Through high cell density fermentation, the maximum yield reached 11,600 U/mL and 15.5 g/L, which is higher than most extreme β-mannanases. The recombinant ManAK was thermostable with a temperature optimum of 80 °C, and acid tolerant with a pH optimum of 2.0. ManAK could efficiently degrade locust bean gum, konjac gum, and guar gum into small molecular mannooligosaccharide (<2000 Da), even at high initial substrate concentration (10%), and displayed different Mw distributions in their end products. Docking analysis demonstrated that the catalytic pocket of ManAK could only accommodate a galactopyranosyl residue in subsite -1, which might be responsible for the distinct hydrolysis product compositions from locust bean gum and guar gum. These superior properties of ManAK strongly facilitate mannooligosaccharide preparation and application in food and feed area.

Production and purification of mannan oligosaccharide with epithelial tight junction enhancing activity

Background

Mannanan oligosaccharide (MOS) is well-known as effective supplement food for livestock to increase their nutrients absorption and health status, but the structure and identification of bioactive MOS remain unclear. In this study, MOS production was accomplished, using enzymatic hydrolysis of pretreated coconut meal substrate with recombinant mannanase.

Methods

The mannanase gene was cloned from Bacillus subtilis cAE24, then expressed in BL21. Purified Mannanase exhibit stability over a wide range of pH and temperature from pH 6-8 and 4 °C to 70 °C, respectively. SEM analysis revealed that sonication could change the surface characteristic of copra meal, which gave better MOS yield, compared to untreated substrates. The separation and purification of each MOS were achieved using Biogel-P2 column chromatography. Determination of biological active MOS species was also investigated. T84 cells were cultured and treated with each of the purified MOS species to determine their tight junction enhancing activity.

Results

Scanning electron microscope imaging showed that pretreatment using sonication could disrupt the surface of copra meal better than grinding alone, which can improve the production of MOS. Pentamer of MOS (M5) significantly increased tight junction integration of T84 cells measured with TEER (p < 0.0001).

Crystal structure determination of Pseudomonas stutzeri A1501 endoglucanase Cel5A: the search for a molecular basis for glycosynthesis in GH5_5 enzymes

The discovery of new glycoside hydrolases that can be utilized in the chemoenzymatic synthesis of carbohydrates has emerged as a promising approach for various biotechnological processes. In this study, recombinant Ps_Cel5A from Pseudomonas stutzeri A1501, a novel member of the GH5_5 subfamily, was expressed, purified and crystallized. Preliminary experiments confirmed the ability of Ps_Cel5A to catalyze transglycosylation with cellotriose as a substrate. The crystal structure revealed several structural determinants in and around the positive subsites, providing a molecular basis for a better understanding of the mechanisms that promote and favour synthesis rather than hydrolysis. In the positive subsites, two nonconserved positively charged residues (Arg178 and Lys216) were found to interact with cellobiose. This adaptation has also been reported for transglycosylating β-mannanases of the GH5_7 subfamily.

Crystal structure and substrate interactions of an unusual fungal non-CBM carrying GH26 endo-β-mannanase from Yunnania penicillata

Endo-β(1 → 4)-mannanases (endomannanases) catalyse degradation of β-mannans, an abundant class of plant polysaccharides. This study investigates structural features and substrate binding of YpenMan26A, a non-CBM carrying endomannanase from Yunnania penicillata. Structural and sequence comparisons to other fungal family GH26 endomannanases showed high sequence similarities and conserved binding residues, indicating that fungal GH26 endomannanases accommodate galactopyranosyl units in the -3 and -2 subsites. Two striking amino acid differences in the active site were found when the YpenMan26A structure was compared to a homology model of Wsp.Man26A from Westerdykella sp. and the sequences of nine other fungal GH26 endomannanases. Two YpenMan26A mutants, W110H and D37T, inspired by differences observed in Wsp.Man26A, produced a shift in how mannopentaose bound across the active site cleft and a decreased affinity for galactose in the -2 subsite, respectively, compared to YpenMan26A. YpenMan26A was moreover found to have a flexible surface loop in the position where PansMan26A from Podospora anserina has an α-helix (α9) which interacts with its family 35 CBM. Sequence alignment inferred that the core structure of fungal GH26 endomannanases differ depending on the natural presence of this type of CBM. These new findings have implications for selecting and optimising these enzymes for galactomannandegradation.

Production optimization and characterization of mannooligosaccharide generating β-mannanase from Aspergillus oryzae

A multi-tolerant β-mannanase (ManAo) was produced by Aspergillus oryzae on copra meal, a low-cost agro waste. Under statistically optimized conditions, 4.3-fold increase in β-mannanase production (434 U/gds) was obtained. Purified ManAo had MW ∼34 kDa and specific activity of 335.85 U/mg with optimum activity at 60 °C and at pH 5.0. Activity of ManAo was enhanced by most metal ions and modulators while maximum enhancement was noticed with Ag⁺ and Triton X-100. K_m and V_max were 2.7 mg/mL and 1388.8 µmol/min/mg for locust bean gum while the enzyme showed lower affinity towards konjac gum (8.8 mg/mL, 555.5 µmol/min/mg). Evaluation of various thermodynamic parameters indicated high-efficiency of the ManAo with activation energy 12.42 KJ/mol and 23.31 KJ/mol towards LBG and konjac gum, respectively. End product analysis of β-mannanase action by fluorescence assisted carbohydrate electrophoresis (FACE) revealed the generation of sugars from DP 1-4 with some higher DP MOS from different mannans.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2013-2014

This review is the eighth update of the original article published in 1999 on the application of Matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2014. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly- saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2018 Wiley Periodicals, Inc. Mass Spec Rev 37:353-491, 2018.

Structural insights into the catalytic mechanism of a novel glycoside hydrolase family 113 β-1,4-mannanase from Amphibacillus xylanus

β-1,4-Mannanase degrades β-1,4-mannan polymers into manno-oligosaccharides with a low degree of polymerization. To date, only one glycoside hydrolase (GH) family 113 β-1,4-mannanase, from Alicyclobacillus acidocaldarius (AaManA), has been structurally characterized, and no complex structure of enzyme-manno-oligosaccharides from this family has been reported. Here, crystal structures of a GH family 113 β-1,4-mannanase from Amphibacillus xylanus (AxMan113A) and its complexes with mannobiose, mannotriose, mannopentaose, and mannahexaose were solved. AxMan113A had higher affinity for -1 and +1 mannoses, which explains why the enzyme can hydrolyze mannobiose. At least six subsites (-4 to +2) exist in the groove, but mannose units preferentially occupied subsites -4 to -1 because of steric hindrance formed by Lys-238 and Trp-239. Based on the structural information and bioinformatics, rational design was implemented to enhance hydrolysis activity. Enzyme activity of AxMan113A mutants V139C, N237W, K238A, and W239Y was improved by 93.7, 63.4, 112.9, and 36.4%, respectively, compared with the WT. In addition, previously unreported surface-binding sites were observed. Site-directed mutagenesis studies and kinetic data indicated that key residues near the surface sites play important roles in substrate binding and recognition. These first GH family 113 β-1,4-mannanase-manno-oligosaccharide complex structures may be useful in further studying the catalytic mechanism of GH family 113 members, and provide novel insight into protein engineering of GHs to improve their hydrolysis activity.

β-Mannanase-catalyzed synthesis of alkyl mannooligosides

β-Mannanases catalyze the conversion and modification of β-mannans and may, in addition to hydrolysis, also be capable of transglycosylation which can result in enzymatic synthesis of novel glycoconjugates. Using alcohols as glycosyl acceptors (alcoholysis), β-mannanases can potentially be used to synthesize alkyl glycosides, biodegradable surfactants, from renewable β-mannans. In this paper, we investigate the synthesis of alkyl mannooligosides using glycoside hydrolase family 5 β-mannanases from the fungi Trichoderma reesei (TrMan5A and TrMan5A-R171K) and Aspergillus nidulans (AnMan5C). To evaluate β-mannanase alcoholysis capacity, a novel mass spectrometry-based method was developed that allows for relative comparison of the formation of alcoholysis products using different enzymes or reaction conditions. Differences in alcoholysis capacity and potential secondary hydrolysis of alkyl mannooligosides were observed when comparing alcoholysis catalyzed by the three β-mannanases using methanol or 1-hexanol as acceptor. Among the three β-mannanases studied, TrMan5A was the most efficient in producing hexyl mannooligosides with 1-hexanol as acceptor. Hexyl mannooligosides were synthesized using TrMan5A and purified using high-performance liquid chromatography. The data suggests a high selectivity of TrMan5A for 1-hexanol as acceptor over water. The synthesized hexyl mannooligosides were structurally characterized using nuclear magnetic resonance, with results in agreement with their predicted β-conformation. The surfactant properties of the synthesized hexyl mannooligosides were evaluated using tensiometry, showing that they have similar micelle-forming properties as commercially available hexyl glucosides. The present paper demonstrates the possibility of using β-mannanases for alkyl glycoside synthesis and increases the potential utilization of renewable β-mannans.

Strategy in manipulating transglycosylation activity of glycosyl hydrolase for oligosaccharide production

BACKGROUND

The increasing market demand for oligosaccharides has intensified the need for efficient biocatalysts. Glycosyl hydrolases (GHs) are still gaining popularity as biocatalyst for oligosaccharides synthesis owing to its simple reaction and high selectivity.

PURPOSE

Over the years, research has advanced mainly directing to one goal; to reduce hydrolysis activity of GHs for increased transglycosylation activity in achieving high production of oligosaccharides.

DESIGN AND METHODS

This review concisely presents the strategies to increase transglycosylation activity of GHs for oligosaccharides synthesis, focusing on controlling the reaction equilibrium, and protein engineering. Various modifications of the subsites of GHs have been demonstrated to significantly modulate the hydrolysis and transglycosylation activity of the enzymes. The clear insight of the roles of each amino acid in these sites provides a platform for designing an enzyme that could synthesize a specific oligosaccharide product.

CONCLUSIONS

The key strategies presented here are important for future improvement of GHs as a biocatalyst for oligosaccharide synthesis.

Production of high activity Aspergillus niger BCC4525 β-mannanase in Pichia pastoris and its application for mannooligosaccharides production from biomass hydrolysis

A cDNA encoding β-mannanase was cloned from Aspergillus niger BCC4525 and expressed in Pichia pastoris KM71. The secreted enzyme hydrolyzed locust bean gum substrate with very high activity (1625 U/mL) and a relatively high kcat/Km (461 mg−1 s−1 mL). The enzyme is thermophilic and thermostable with an optimal temperature of 70 °C and 40% retention of endo-β-1,4-mannanase activity after preincubation at 70 °C. In addition, the enzyme exhibited broad pH stability with an optimal pH of 5.5. The recombinant enzyme hydrolyzes low-cost biomass, including palm kernel meal (PKM) and copra meal, to produce mannooligosaccharides, which is used as prebiotics to promote the growth of beneficial microflora in animals. An in vitro digestibility test simulating the gastrointestinal tract system of broilers suggested that the recombinant β-mannanase could effectively liberate reducing sugars from PKM-containing diet. These characteristics render this enzyme suitable for utilization as a feed additive to improve animal performance.

A Novel Glycoside Hydrolase Family 113 Endo-β-1,4-Mannanase from Alicyclobacillus sp. Strain A4 and Insight into the Substrate Recognition and Catalytic Mechanism of This Family

Few members of glycoside hydrolase (GH) family 113 have been characterized, and information on substrate recognition by and the catalytic mechanism of this family is extremely limited. In the present study, a novel endo-β-1,4-mannanase of GH 113, Man113A, was identified in thermoacidophilic Alicyclobacillus sp. strain A4 and found to exhibit both hydrolytic and transglycosylation activities. The enzyme had a broad substrate spectrum, showed higher activities on glucomannan than on galactomannan, and released mannobiose and mannotriose as the main hydrolysis products after an extended incubation. Compared to the only functionally characterized and structure-resolved counter part Alicyclobacillus acidocaldarius ManA (AaManA) of GH 113, Man113A showed much higher catalytic efficiency on mannooligosaccharides, in the order mannohexaose ≈ mannopentaose > mannotetraose > mannotriose, and required at least four sugar units for efficient catalysis. Homology modeling, molecular docking analysis, and site-directed mutagenesis revealed the vital roles of eight residues (Trp13, Asn90, Trp96, Arg97, Tyr196, Trp274, Tyr292, and Cys143) related to substrate recognition by and catalytic mechanism of GH 113. Comparison of the binding pockets and key residues of β-mannanases of different families indicated that members of GH 113 and GH 5 have more residues serving as stacking platforms to support -4 to -1 subsites than those of GH 26 and that the residues preceding the acid/base catalyst are quite different. Taken as a whole, this study elucidates substrate recognition by and the catalytic mechanism of GH 113 β-mannanases and distinguishes them from counterparts of other families.

Insights into the plant polysaccharide degradation potential of the xylanolytic yeast Pseudozyma brasiliensis

In second-generation (2G) bioethanol production, plant cell-wall polysaccharides are broken down to release fermentable sugars. The enzymes of this process are classified as carbohydrate-active enzymes (CAZymes) and contribute substantially to the cost of biofuel production. A novel basidiomycete yeast species, Pseudozyma brasiliensis, was recently discovered. It produces an endo-β-1,4-xylanase with a higher specific activity than other xylanases. This enzyme is essential for the hydrolysis of biomass-derived xylan and has an important role in 2G bioethanol production. In spite of the P. brasiliensis biotechnological potential, there is no information about how it breaks down polysaccharides. For the first time, we characterized the secretome of P. brasiliensis grown on different carbon sources (xylose, xylan, cellobiose and glucose) and also under starvation conditions. The growth and consumption of each carbohydrate and the activity of the CAZymes of culture supernatants were analyzed. The CAZymes found in its secretomes, validated by enzymatic assays, have the potential to hydrolyze xylan, mannan, cellobiose and other polysaccharides. The data show that this yeast is a potential source of hydrolases, which can be used for biomass saccharification.

Biochemical characterization of the novel endo-β-mannanase AtMan5-2 from Arabidopsis thaliana

Plant mannanases are enzymes that carry out fundamentally important functions in cell wall metabolism during plant growth and development by digesting manno-polysaccharides. In this work, the Arabidopsis mannanase 5-2 (AtMan5-2) from a previously uncharacterized subclade of glycoside hydrolase family 5 subfamily 7 (GH5_7) has been heterologously produced in Pichia pastoris. Purified recombinant AtMan5-2 is a glycosylated protein with an apparent molecular mass of 50kDa, a pH optimum of 5.5-6.0 and a temperature optimum of 25°C. The enzyme exhibits high substrate affinity and catalytic efficiency on mannan substrates with main chains containing both glucose and mannose units such as konjac glucomannan and spruce galactoglucomannan. Product analysis of manno-oligosaccharide hydrolysis shows that AtMan5-2 requires at least six substrate-binding subsites. No transglycosylation activity for the recombinant enzyme was detected in the present study. Our results demonstrate diversification of catalytic function among members in the Arabidopsis GH5_7 subfamily.

The GH5 1,4-β-mannanase from Bifidobacterium animalis subsp. lactis Bl-04 possesses a low-affinity mannan-binding module and highlights the diversity of mannanolytic enzymes

Background

β-Mannans are abundant and diverse plant structural and storage polysaccharides. Certain human gut microbiota members including health-promoting Bifidobacterium spp. catabolize dietary mannans. Little insight is available on the enzymology of mannan deconstruction in the gut ecological niche. Here, we report the biochemical properties of the first family 5 subfamily 8 glycoside hydrolase (GH5_8) mannanase from the probiotic bacterium Bifidobacterium animalis subsp. lactis Bl-04 (BlMan5_8).

Results

BlMan5_8 possesses a novel low affinity carbohydrate binding module (CBM) specific for soluble mannan and displays the highest catalytic efficiency reported to date for a GH5 mannanase owing to a very high k_cat (1828 ± 87 s^-1) and a low K_m (1.58 ± 0.23 g · L^-1) using locust bean galactomannan as substrate. The novel CBM of BlMan5_8 mediates increased binding to soluble mannan based on affinity electrophoresis. Surface plasmon resonance analysis confirmed the binding of the CBM10 to manno-oligosaccharides, albeit with slightly lower affinity than the catalytic module of the enzyme. This is the first example of a low-affinity mannan-specific CBM, which forms a subfamily of CBM10 together with close homologs present only in mannanases. Members of this new subfamily lack an aromatic residue mediating binding to insoluble cellulose in canonical CBM10 members consistent with the observed low mannan affinity.

Conclusion

BlMan5_8 is evolved for efficient deconstruction of soluble mannans, which is reflected by an exceptionally low K_m and the presence of an atypical low affinity CBM, which increases binding to specifically to soluble mannan while causing minimal decrease in catalytic efficiency as opposed to enzymes with canonical mannan binding modules. These features highlight fine tuning of catalytic and binding properties to support specialization towards a preferred substrate, which is likely to confer an advantage in the adaptation to competitive ecological niches.

Electronic supplementary material

The online version of this article (doi:10.1186/s12858-015-0055-4) contains supplementary material, which is available to authorized users.

An Aspergillus nidulans GH26 endo-β-mannanase with a novel degradation pattern on highly substituted galactomannans

The activity and substrate degradation pattern of a novel Aspergillus nidulans GH26 endo-β-mannanase (AnMan26A) was investigated using two galactomannan substrates with varying amounts of galactopyranosyl residues. The AnMan26A was characterized in parallel with the GH26 endomannanase from Podospora anserina (PaMan26A) and three GH5 endomannanases from A. nidulans and Trichoderma reesei (AnMan5A, AnMan5C and TrMan5A). The initial rates and the maximal degree of enzymatically catalyzed conversion of locust bean gum and guar gum galactomannans were determined. The hydrolysis product profile at maximal degree of conversion was determined using DNA sequencer-Assisted Saccharide analysis in High throughput (DASH). This is the first reported use of this method for analyzing galactomannooligosaccharides. AnMan26A and PaMan26A were found to have a novel substrate degradation pattern on the two galactomannan substrates. On the highly substituted guar gum AnMan26A and PaMan26A reached 35-40% as their maximal degree of conversion whereas the three tested GH5 endomannanases only reached 8-10% as their maximal degree of conversion. α-Galactosyl-mannose was identified as the dominant degradation product resulting from AnMan26A and PaMan26A action on guar gum, strongly indicating that these two enzymes can accommodate galactopyranosyl residues in the -1 and in the +1 subsite. The degradation of α-6(4)-6(3)-di-galactosyl-mannopentaose by AnMan26A revealed accommodation of galactopyranosyl residues in the -2, -1 and +1 subsite of the enzyme. Accommodation of galactopyranosyl residues in subsites -2 and +1 has not been observed for other characterized endomannanases to date. Docking analysis of galactomannooligosaccharides in available crystal structures and homology models supported the conclusions drawn from the experimental results. This newly discovered diversity of substrate degradation patterns demonstrates an expanded functionality of fungal endomannanases, than hitherto reported.

Novel β-1,4-Mannanase Belonging to a New Glycoside Hydrolase Family in Aspergillus nidulans

Many filamentous fungi produce β-mannan-degrading β-1,4-mannanases that belong to the glycoside hydrolase 5 (GH5) and GH26 families. Here we identified a novel β-1,4-mannanase (Man134A) that belongs to a new glycoside hydrolase (GH) family (GH134) in Aspergillus nidulans. Blast analysis of the amino acid sequence using the NCBI protein database revealed that this enzyme had no similarity to any sequences and no putative conserved domains. Protein homologs of the enzyme were distributed to limited fungal and bacterial species. Man134A released mannobiose (M₂), mannotriose (M₃), and mannotetraose (M₄) but not mannopentaose (M₅) or higher manno-oligosaccharides when galactose-free β-mannan was the substrate from the initial stage of the reaction, suggesting that Man134A preferentially reacts with β-mannan via a unique catalytic mode. Man134A had high catalytic efficiency (k_cat/K_m) toward mannohexaose (M₆) compared with the endo-β-1,4-mannanase Man5C and notably converted M₆ to M₂, M₃, and M₄, with M₃ being the predominant reaction product. The action of Man5C toward β-mannans was synergistic. The growth phenotype of a Man134A disruptant was poor when β-mannans were the sole carbon source, indicating that Man134A is involved in β-mannan degradation in vivo. These findings indicate a hitherto undiscovered mechanism of β-mannan degradation that is enhanced by the novel β-1,4-mannanase, Man134A, when combined with other mannanolytic enzymes including various endo-β-1,4-mannanases.