A thermostable GH45 endoglucanase from yeast: impact of its atypical multimodularity on activity

The first crystal structure of a family 45 glycoside hydrolase from a brown-rot fungus, Gloeophyllum trabeum GtCel45A

Here we describe the first crystal structure of a beta-1,4-endoglucanase from a brown-rot fungus, Gloeophyllum trabeum GtCel45A, which belongs to subfamily C of glycoside hydrolase family 45 (GH45). GtCel45A is ~ 18 kDa in size and the crystal structure contains 179 amino acids. The structure is refined at 1.30 Å resolution and Rfree 0.18. The enzyme consists of a single catalytic module folded into a six-stranded double-psi beta-barrel domain surrounded by long loops. GtCel45A is very similar in sequence (82% identity) and structure to PcCel45A from the white-rot fungus Phanerochaete chrysosporium. Surprisingly though, initial hydrolysis of barley beta-glucan was almost twice as fast in GtCel45A as compared to PcCel45A.

Characterization of Paenibacillus sp. GKG Endo-β-1, 3-Glucanase, a Member of Family 81 Glycoside Hydrolases

Paenibacillus sp. GKG was isolated based on its ability to produce hydrolysis zones on agar plates containing yeast cell wall substrate as the single carbon source. The extracellular enzymes secreted into the culture medium were identified by LC-MS/MS proteomics. Endo-β-1,3-glucanase PsLam81A containing GH81 catalytic and the CBM56 carbohydrate-binding modules was selected for heterologous expression in Escherichia coli. The identity of the recombinant PsLam81A was confirmed by LC-MS/MS proteomics. The PsLam81A showed the highest activity at 60 °C, and the optimal pH range was between 6.5 and 8.0. The analysis of the full-length PsLam81A and truncated PsLam81AΔCBM56 enzymes showed that the CBM56 module improved the hydrolytic activity towards linear β-1,3-glucans-curdlan and pachyman but had no effect on hydrolysis of β-1,3/β1,6-branched glucans-laminarin and yeast β-glucan. The characterization of PsLam81A enzyme broadens current knowledge on the biochemical properties and substrate specificity of family 81 glycoside hydrolases and allows prediction of the necessity of CBM56 module in the process of designing new truncated or chimeric glycosidases.

Heterologous expression and characterization of a novel lytic polysaccharide monooxygenase from Natrialbaceae archaeon and its application for chitin biodegradation

Lytic polysaccharide monooxygenases could enhance the enzymatic conversion of recalcitrant polysaccharides by glycoside hydrolases. This study reports the expression and identification of a novel AA10 LPMO from Natrialbaceae archaeon, named NaLPMO10A, as a C1 oxidizer of chitin. The optimal temperature and pH for NaLPMO10A activity were 40 °C and 9.0, respectively, and NaLPMO10A exhibited high thermostability and pH stability under alkaline conditions. NaLPMO10A was also highly tolerant and stable when treated with high concentration of metal ions (1 M). Moreover, metal ions (Na⁺, K⁺, Ca²⁺ and Mg²⁺) significantly promoted NaLPMO10A activity and improved the saccharification efficiency of chitin by 22.6%, 45.9%, 36.7% and 53.9%, respectively, compared to commercial chitinase alone. Together, the findings of this study fill a gap in archaeal LPMO research, and for the first time demonstrate that archaeal NaLPMO10A could be a promising enzyme for improving saccharification under extreme condition, with potential applications in biorefineries.

Comparison of the Biochemical Properties and Roles in the Xyloglucan-Rich Biomass Degradation of a GH74 Xyloglucanase and Its CBM-Deleted Variant from Thielavia terrestris

Xyloglucan is closely associated with cellulose and still retained with some modification in pretreated lignocellulose; however, its influence on lignocellulose biodegradation is less understood. TtGH74 from Thielavia terrestris displayed much higher catalytic activity than previously characterized fungal GH74 xyloglucanases. The carbohydrate-binding module 1 (CBM1) deleted variant (TtGH74ΔCBM) had the same optimum temperature and pH but an elevated thermostability. TtGH74 displayed a high binding affinity on xyloglucan and cellulose, while TtGH74ΔCBM completely lost the adsorption capability on cellulose. Their hydrolysis action alone or in combination with other glycoside hydrolases on the free xyloglucan, xyloglucan-coated phosphoric acid-swollen cellulose or pretreated corn bran and apple pomace was compared. CBM1 might not be essential for the hydrolysis of free xyloglucan but still effective for the associated xyloglucan to an extent. TtGH74 alone or synergistically acting with the CBH1/EG1 mixture was more effective in the hydrolysis of xyloglucan in corn bran, while TtGH74ΔCBM showed relatively higher catalytic activity on apple pomace, indicating that the role and significance of CBM1 are substrate-specific. The degrees of synergy for TtGH74 or TtGH74ΔCBM with the CBH1/EG1 mixture reached 1.22–2.02. The addition of GH10 xylanase in TtGH74 or the TtGH74ΔCBM/CBH1/EG1 mixture further improved the overall hydrolysis efficiency, and the degrees of synergy were up to 1.50–2.16.

The ectomycorrhizal basidiomycete Laccaria bicolor releases a GH28 polygalacturonase that plays a key role in symbiosis establishment

In ectomycorrhiza, root penetration and colonization of the intercellular space by symbiotic hyphae is thought to rely on the mechanical force that results from hyphal tip growth, enhanced by the activity of secreted cell-wall-degrading enzymes. Here, we characterize the biochemical properties of the symbiosis-induced polygalacturonase LbGH28A from the ectomycorrhizal fungus Laccaria bicolor. The transcriptional regulation of LbGH28A was measured by quantitative PCR (qPCR). The biological relevance of LbGH28A was confirmed by generating RNA interference (RNAi)-silenced LbGH28A mutants. We localized the LbGH28A protein by immunofluorescence confocal and immunogold cytochemical microscopy in poplar ectomycorrhizal roots. Quantitative PCR confirmed the induced expression of LbGH28A during ectomycorrhiza formation. Laccaria bicolor RNAi mutants have a lower ability to establish ectomycorrhiza, confirming the key role of this enzyme in symbiosis. The purified recombinant LbGH28A has its highest activity towards pectin and polygalacturonic acid. In situ localization of LbGH28A indicates that this endopolygalacturonase is located in both fungal and plant cell walls at the symbiotic hyphal front. These findings suggest that the symbiosis-induced pectinase LbGH28A is involved in the Hartig net formation and is an important determinant for successful symbiotic colonization.

Glucomannan and beta-glucan degradation by Mytilus edulis Cel45A: Crystal structure and activity comparison with GH45 subfamily A, B and C

The enzymatic hydrolysis of barley beta-glucan, konjac glucomannan and carboxymethyl cellulose by a β-1,4-D-endoglucanase MeCel45A from blue mussel, Mytilus edulis, which belongs to subfamily B of glycoside hydrolase family 45 (GH45), was compared with GH45 members of subfamilies A (Humicola insolens HiCel45A), B (Trichoderma reesei TrCel45A) and C (Phanerochaete chrysosporium PcCel45A). Furthermore, the crystal structure of MeCel45A is reported. Initial rates and hydrolysis yields were determined by reducing sugar assays and product formation was characterized using NMR spectroscopy. The subfamily B and C enzymes exhibited mannanase activity, whereas the subfamily A member was uniquely able to produce monomeric glucose. All enzymes were confirmed to be inverting glycoside hydrolases. MeCel45A appears to be cold adapted by evolution, as it maintained 70% activity on cellohexaose at 4 °C relative to 30 °C, compared to 35% for TrCel45A. Both enzymes produced cellobiose and cellotetraose from cellohexaose, but TrCel45A additionally produced cellotriose.

Expression and characterization of a family 45 glycosyl hydrolase from Fomitopsis pinicola and comparison to Phanerochaete chrysosporium Cel45A

To efficiently decompose biomass, fungi have developed various enzymatic and non-enzymatic strategies and are a source of versatile biocatalysts. The endoglucanases in glycosyl hydrolase CAZy family 45 (GH45) are known for their small size, a high thermostability and a broad substrate specificity that has been employed in textile and detergent industries. Here we report the heterologous expression and characterisation of an GH45 endoglucanase from the brown rot Fomitopsis pinicola and its direct comparison to an already characterised GH45 from the white rot Phanerochaete chrysosporium. Both enzymes were recombinantly expressed in Pichia pastoris and purified by two chromatographic steps. The biochemical characterisation highlighted the acidophilic character, with an optimal pH of 4, and a preference for amorphous substrates as carboxymethyl cellulose (CMC) and substrates containing β-1,4-glucans rather than the previously reported β-1,3/1,4-glucans lichenan and β-glucan. The dominating products from β-1,4-glucans were C3-C6 oligosaccharides, whereas from β-1,3/1,4-glucans glucose was the main reaction product. From the characterisation no differences between the brown rot and the white rot GH45 was evident.

Carbohydrate Binding Modules: Diversity of Domain Architecture in Amylases and Cellulases From Filamentous Microorganisms

Enzymatic degradation of abundant renewable polysaccharides such as cellulose and starch is a field that has the attention of both the industrial and scientific community. Most of the polysaccharide degrading enzymes are classified into several glycoside hydrolase families. They are often organized in a modular manner which includes a catalytic domain connected to one or more carbohydrate-binding modules. The carbohydrate-binding modules (CBM) have been shown to increase the proximity of the enzyme to its substrate, especially for insoluble substrates. Therefore, these modules are considered to enhance enzymatic hydrolysis. These properties have played an important role in many biotechnological applications with the aim to improve the efficiency of polysaccharide degradation. The domain organization of glycoside hydrolases (GHs) equipped with one or more CBM does vary within organisms. This review comprehensively highlights the presence of CBM as ancillary modules and explores the diversity of GHs carrying one or more of these modules that actively act either on cellulose or starch. Special emphasis is given to the cellulase and amylase distribution within the filamentous microorganisms from the genera of Streptomyces and Aspergillus that are well known to have a great capacity for secreting a wide range of these polysaccharide degrading enzyme. The potential of the CBM and other ancillary domains for the design of improved polysaccharide decomposing enzymes is discussed.

Structural insights into the hydrolysis pattern and molecular dynamics simulations of GH45 subfamily a endoglucanase from Neurospora crassa OR74A

Glycoside hydrolase (GH) family 45 is one of the smallest and poorly studied endoglucanase family with a broad biotechnological application ranging from treatment of textiles to conversion of complex cell wall polysaccharides into simple oligo- and monosaccharides. In a present study, GH45 cellulase from Neurospora crassa OR74A (NcCel45A) was characterized both biochemically and structurally. HPLC analysis of the hydrolytic products confirmed the endo-β(1,4) mode of action of the enzyme. Moreover, such pattern revealed that NcCel45A cannot hydrolyze efficiently oligosaccharides with a degree of polymerization smaller than six. The crystal structure of NcCel45A catalytic domain in the apo-form was determined at 1.9 Å resolution and the structure of the enzyme bound to cellobiose was solved and refined to 1.8 Å resolution. Comparative structural analyses and molecular dynamics simulations show that the enzyme dynamics is affected by substrate binding. Taken together, MD simulations and statistical coupling analysis revealed previously unknown correlation of a loop 6 with the breakdown of cellulose substrates by GH45.

High-resolution crystal structures of the glycoside hydrolase family 45 endoglucanase EG27II from the snail Ampullaria crossean

Although endogenous animal cellulases have great potential for industrial applications such as bioethanol production, few investigations have focused on these enzymes. In this study, the glycoside hydrolase family 45 (GH45) subfamily B endoglucanase EG27II from the snail Ampullaria crossean was expressed using a Pichia pastoris expression system and the crystal structure of the apo form was determined at 1.00 Å resolution; this is the highest resolution structure of an animal endoglucanase. The results showed that EG27II has a double-ψ six-stranded β-barrel and that the structure of EG27II more closely resembles those of subfamily C enzymes than those of subfamily A enzymes. The structure of EG27II complexed with cellobiose was also determined under cryoconditions and at room temperature at three pH values, pH 4.0, 5.5 and 8.0, and no structural changes were found to be associated with the change in pH. The structural comparison and catalytic activity measurements showed that Asp137 and Asn112 function as the catalytic acid and base, respectively, and that Asp27 is also an important residue for catalysis. These high-resolution structures of EG27II provide a large amount of information for structure-based enzyme modification and cell-surface engineering, which will advance biofuel production using animal-derived cellulases.

Influence of the carbohydrate-binding module on the activity of a fungal AA9 lytic polysaccharide monooxygenase on cellulosic substrates

BACKGROUND

Cellulose-active lytic polysaccharide monooxygenases (LPMOs) secreted by filamentous fungi play a key role in the degradation of recalcitrant lignocellulosic biomass. They can occur as multidomain proteins fused to a carbohydrate-binding module (CBM). From a biotech perspective, LPMOs are promising innovative tools for producing nanocelluloses and biofuels, but their direct action on cellulosic substrates is not fully understood.

RESULTS

In this study, we probed the role of the CBM from family 1 (CBM1) appended to the LPMO9H from Podospora anserina (PaLPMO9H) using model cellulosic substrates. Deletion of the CBM1 weakened the binding to cellulose nanofibrils, amorphous and crystalline cellulose. Although the release of soluble sugars from cellulose was drastically reduced under standard conditions, the truncated LPMO retained some activity on soluble oligosaccharides. The cellulolytic action of the truncated LPMO was demonstrated using synergy experiments with a cellobiohydrolase (CBH). The truncated LPMO was still able to improve the efficiency of the CBH on cellulose nanofibrils in the same range as the full-length LPMO. Increasing the substrate concentration enhanced the performance of PaLPMO9H without CBM in terms of product release. Interestingly, removing the CBM also altered the regioselectivity of PaLPMO9H, significantly increasing cleavage at the C1 position. Analysis of the insoluble fraction of cellulosic substrates evaluated by optical and atomic force microscopy confirmed that the CBM1 module was not strictly required to promote disruption of the cellulose network.

CONCLUSIONS

Absence of the CBM1 does not preclude the activity of the LPMO on cellulose but its presence has an important role in driving the enzyme to the substrate and releasing more soluble sugars (both oxidized and non-oxidized), thus facilitating the detection of LPMO activity at low substrate concentration. These results provide insights into the mechanism of action of fungal LPMOs on cellulose to produce nanocelluloses and biofuels.

The ectomycorrhizal basidiomycete Laccaria bicolor releases a secreted β-1,4 endoglucanase that plays a key role in symbiosis development

In ectomycorrhiza, root ingress and colonization of the apoplast by colonizing hyphae is thought to rely mainly on the mechanical force that results from hyphal tip growth, but this could be enhanced by secretion of cell-wall-degrading enzymes, which have not yet been identified. The sole cellulose-binding module (CBM1) encoded in the genome of the ectomycorrhizal Laccaria bicolor is linked to a glycoside hydrolase family 5 (GH5) endoglucanase, LbGH5-CBM1. Here, we characterize LbGH5-CBM1 gene expression and the biochemical properties of its protein product. We also immunolocalized LbGH5-CBM1 by immunofluorescence confocal microscopy in poplar ectomycorrhiza. We show that LbGH5-CBM1 expression is substantially induced in ectomycorrhiza, and RNAi mutants with a decreased LbGH5-CBM1 expression have a lower ability to form ectomycorrhiza, suggesting a key role in symbiosis. Recombinant LbGH5-CBM1 displays its highest activity towards cellulose and galactomannans, but no activity toward L. bicolor cell walls. In situ localization of LbGH5-CBM1 in ectomycorrhiza reveals that the endoglucanase accumulates at the periphery of hyphae forming the Hartig net and the mantle. Our data suggest that the symbiosis-induced endoglucanase LbGH5-CBM1 is an enzymatic effector involved in cell wall remodeling during formation of the Hartig net and is an important determinant for successful symbiotic colonization.

Cellulases from Thermophiles Found by Metagenomics

Cellulases are a heterogeneous group of enzymes that synergistically catalyze the hydrolysis of cellulose, the major component of plant biomass. Such reaction has biotechnological applications in a broad spectrum of industries, where they can provide a more sustainable model of production. As a prerequisite for their implementation, these enzymes need to be able to operate in the conditions the industrial process requires. Thus, cellulases retrieved from extremophiles, and more specifically those of thermophiles, are likely to be more appropriate for industrial needs in which high temperatures are involved. Metagenomics, the study of genes and gene products from the whole community genomic DNA present in an environmental sample, is a powerful tool for bioprospecting in search of novel enzymes. In this review, we describe the cellulolytic systems, we summarize their biotechnological applications, and we discuss the strategies adopted in the field of metagenomics for the discovery of new cellulases, focusing on those of thermophilic microorganisms.

Engineering the conserved and noncatalytic residues of a thermostable β-1,4-endoglucanase to improve specific activity and thermostability

Endoglucanases are increasingly applied in agricultural and industrial applications as a key biocatalyst for cellulose biodegradation. However, the low performance in extreme conditions seriously challenges the enzyme’s commercial utilization. To obtain endoglucanases with substantially improved activity and thermostability, structure-based rational design was carried out based on the Chaetomium thermophilum β-1,4-endoglucanase CTendo45. In this study, five mutant enzymes were constructed by substitution of conserved and noncatalytic residues using site-directed mutagenesis. Mutants were constitutively expressed in Pichia pastoris, purified, and ultimately tested for enzymatic characteristics. Two single mutants, Y30F and Y173F, increased the enzyme’s specific activity 1.35- and 1.87-fold using carboxymethylcellulose sodium (CMC-Na) as a substrate, respectively. Furthermore, CTendo45 and mutants exhibited higher activity towards β-D-glucan than that of CMC-Na, and activities of Y173F and Y30F were also increased obviously against β-D-glucan. In addition, Y173F significantly improved the enzyme’s heat resistance at 80 °C and 90 °C. More interestingly, the double mutant Y30F/Y173F obtained considerably higher stability at elevated temperatures but failed to inherit the increased catalytic efficiency of its single mutant counterparts. This work gives an initial insight into the biological function of conserved and noncatalytic residues of thermostable endoglucanases and proposes a feasible path for the improvement of enzyme redesign proposals.

The yeast Geotrichum candidum encodes functional lytic polysaccharide monooxygenases

BACKGROUND

Lytic polysaccharide monooxygenases (LPMOs) are a class of powerful oxidative enzymes that have revolutionized our understanding of lignocellulose degradation. Fungal LPMOs of the AA9 family target cellulose and hemicelluloses. AA9 LPMO-coding genes have been identified across a wide range of fungal saprotrophs (Ascomycotina, Basidiomycotina, etc.), but so far they have not been found in more basal lineages. Recent genome analysis of the yeast Geotrichum candidum (Saccharomycotina) revealed the presence of several LPMO genes, which belong to the AA9 family.

RESULTS

In this study, three AA9 LPMOs from G. candidum were successfully produced and biochemically characterized. The use of native signal peptides was well suited to ensure correct processing and high recombinant production of GcLPMO9A, GcLPMO9B, and GcLPMO9C in Pichia pastoris. We show that GcLPMO9A and GcLPMO9B were both active on cellulose and xyloglucan, releasing a mixture of soluble C1- and C4-oxidized oligosaccharides from cellulose. All three enzymes disrupted cellulose fibers and significantly improved the saccharification of pretreated lignocellulosic biomass upon addition to a commercial cellulase cocktail.

CONCLUSIONS

The unique enzymatic arsenal of G. candidum compared to other yeasts could be beneficial for plant cell wall decomposition in a saprophytic or pathogenic context. From a biotechnological point of view, G. candidum LPMOs are promising candidates to further enhance enzyme cocktails used in biorefineries such as consolidated bioprocessing.

Deleting the Ig-Like Domain of Alicyclobacillus acidocaldarius Endoglucanase Cel9A Causes a Simultaneous Increase in the Activity and Stability

Endoglucanase Cel9A from Alicyclobacillus acidocaldarius (AaCel9A) is a monomeric enzyme with 537 residues. This enzyme has an Ig-like domain in the N-terminus of the catalytic domain. In this study, the role of the Ig-like domain on the activity, stability, and structural rigidity of AaCel9A and the effect of calcium on enzyme activity and stability were examined by comparing a truncated enzyme with deletion of the Ig-like domain (AaCel9AΔN) to the wild-type enzyme. Our results showed that the deletion of the Ig-like domain increased the catalytic efficiency of the truncated enzyme up to threefold without any significant changes in the K m of the enzyme. Furthermore, pH and temperature optimum for activity were shifted from 6.5 to 7.5 and from 65 to 60 °C, respectively, by deletion of the Ig-like domain. The thermal stability and fluorescence quenching results indicated that the stability and rigidity of the truncated enzyme have been more than that of the wild-type enzyme. Calcium similarly increased the catalytic efficiency of the enzymes (up to 40 %) and remarkably raised the stability of the AaCel9A compared to the AaCel9AΔN. This shows that Ig-like domain has a role in the increase of the enzyme stability by calcium in the wild-type enzyme.

Lytic polysaccharide monooxygenases from Myceliophthora thermophila C1 differ in substrate preference and reducing agent specificity

BACKGROUND

Lytic polysaccharide monooxgygenases (LPMOs) are known to boost the hydrolytic breakdown of lignocellulosic biomass, especially cellulose, due to their oxidative mechanism. For their activity, LPMOs require an electron donor for reducing the divalent copper cofactor. LPMO activities are mainly investigated with ascorbic acid as a reducing agent, but little is known about the effect of plant-derived reducing agents on LPMOs activity.

RESULTS

Here, we show that three LPMOs from the fungus Myceliophthora thermophila C1, MtLPMO9A, MtLPMO9B and MtLPMO9C, differ in their substrate preference, C1-/C4-regioselectivity and reducing agent specificity. MtLPMO9A generated C1- and C4-oxidized, MtLPMO9B C1-oxidized and MtLPMO9C C4-oxidized gluco-oligosaccharides from cellulose. The recently published MtLPMO9A oxidized, next to cellulose, xylan, β-(1 → 3, 1 → 4)-glucan and xyloglucan. In addition, MtLPMO9C oxidized, to a minor extent, xyloglucan and β-(1 → 3, 1 → 4)-glucan from oat spelt at the C4 position. In total, 34 reducing agents, mainly plant-derived flavonoids and lignin-building blocks, were studied for their ability to promote LPMO activity. Reducing agents with a 1,2-benzenediol or 1,2,3-benzenetriol moiety gave the highest release of oxidized and non-oxidized gluco-oligosaccharides from cellulose for all three MtLPMOs. Low activities toward cellulose were observed in the presence of monophenols and sulfur-containing compounds.

CONCLUSIONS

Several of the most powerful LPMO reducing agents of this study serve as lignin building blocks or protective flavonoids in plant biomass. Our findings support the hypothesis that LPMOs do not only vary in their C1-/C4-regioselectivity and substrate specificity, but also in their reducing agent specificity. This work strongly supports the idea that the activity of LPMOs toward lignocellulosic biomass does not only depend on the ability to degrade plant polysaccharides like cellulose, but also on their specificity toward plant-derived reducing agents in situ.

Investigation of the binding properties of a multi-modular GH45 cellulase using bioinspired model assemblies

BACKGROUND

Enzymes degrading plant biomass polymers are widely used in biotechnological applications. Their efficiency can be limited by non-specific interactions occurring with some chemical motifs. In particular, the lignin component is known to bind enzymes irreversibly. In order to determine interactions of enzymes with their substrates, experiments are usually performed on isolated simple polymers which are not representative of plant cell wall complexity. But when using natural plant substrates, the role of individual chemical and structural features affecting enzyme-binding properties is also difficult to decipher.

RESULTS

We have designed and used lignified model assemblies of plant cell walls as templates to characterize binding properties of multi-modular cellulases. These three-dimensional assemblies are modulated in their composition using the three principal polymers found in secondary plant cell walls (cellulose, hemicellulose, and lignin). Binding properties of enzymes are obtained from the measurement of their mobility that depends on their interactions with the polymers and chemical motifs of the assemblies. The affinity of the multi-modular GH45 cellulase was characterized using a statistical analysis to determine the role played by each assembly polymer. Presence of hemicellulose had much less impact on affinity than cellulose and model lignin. Depending on the number of CBMs appended to the cellulase catalytic core, binding properties toward cellulose and lignin were highly contrasted.

CONCLUSIONS

Model assemblies bring new insights into the molecular determinants that are responsible for interactions between enzymes and substrate without the need of complex analysis. Consequently, we believe that model bioinspired assemblies will provide relevant information for the design and optimization of enzyme cocktails in the context of biorefineries.

Recombinant protein production facility for fungal biomass-degrading enzymes using the yeast Pichia pastoris

Filamentous fungi are the predominant source of lignocellulolytic enzymes used in industry for the transformation of plant biomass into high-value molecules and biofuels. The rapidity with which new fungal genomic and post-genomic data are being produced is vastly outpacing functional studies. This underscores the critical need for developing platforms dedicated to the recombinant expression of enzymes lacking confident functional annotation, a prerequisite to their functional and structural study. In the last decade, the yeast Pichia pastoris has become increasingly popular as a host for the production of fungal biomass-degrading enzymes, and particularly carbohydrate-active enzymes (CAZymes). This study aimed at setting-up a platform to easily and quickly screen the extracellular expression of biomass-degrading enzymes in P. pastoris. We first used three fungal glycoside hydrolases (GHs) that we previously expressed using the protocol devised by Invitrogen to try different modifications of the original protocol. Considering the gain in time and convenience provided by the new protocol, we used it as basis to set-up the facility and produce a suite of fungal CAZymes (GHs, carbohydrate esterases and auxiliary activity enzyme families) out of which more than 70% were successfully expressed. The platform tasks range from gene cloning to automated protein purifications and activity tests, and is open to the CAZyme users' community.

Site-Directed Mutagenesis of a Hyperthermophilic Endoglucanase Cel12B from Thermotoga maritima Based on Rational Design

To meet the demand for the application of high activity and thermostable cellulases in the production of new-generation bioethanol from nongrain-cellulose sources, a hyperthermostable β-1,4-endoglucase Cel12B from Thermotoga maritima was selected for further modification by gene site-directed mutagenesis method in the present study, based on homology modeling and rational design. As a result, two recombinant enzymes showed significant improvement in enzyme activity by 77% and 87%, respectively, higher than the parental enzyme TmCel12B. Furthermore, the two mutants could retain 80% and 90.5% of their initial activity after incubation at 80°C for 8 h, while only 45% for 5 h to TmCel12B. The Km and Vmax of the two recombinant enzymes were 1.97±0.05 mM, 4.23±0.15 μmol·mg(-1)·min(-1) of TmCel12B-E225H-K207G-D37V, and 2.97±0.12 mM, 3.15±0.21 μmol·mg(-1)·min(-1) of TmCel12B-E225H-K207G, respectively, when using CMC-Na as the substrate. The roles of the mutation sites were also analyzed and evaluated in terms of electron density, hydrophobicity of the modeled protein structures. The recombinant enzymes may be used in the hydrolysis of cellulose at higher temperature in the future. It was concluded that the gene mutagenesis approach of a certain active residues may effectively improve the performance of cellulases for the industrial applications and contribute to the study the thermostable mechanism of thermophilic enzymes.

Differential gene retention as an evolutionary mechanism to generate biodiversity and adaptation in yeasts

The evolutionary history of the characters underlying the adaptation of microorganisms to food and biotechnological uses is poorly understood. We undertook comparative genomics to investigate evolutionary relationships of the dairy yeast Geotrichum candidum within Saccharomycotina. Surprisingly, a remarkable proportion of genes showed discordant phylogenies, clustering with the filamentous fungus subphylum (Pezizomycotina), rather than the yeast subphylum (Saccharomycotina), of the Ascomycota. These genes appear not to be the result of Horizontal Gene Transfer (HGT), but to have been specifically retained by G. candidum after the filamentous fungi-yeasts split concomitant with the yeasts' genome contraction. We refer to these genes as SRAGs (Specifically Retained Ancestral Genes), having been lost by all or nearly all other yeasts, and thus contributing to the phenotypic specificity of lineages. SRAG functions include lipases consistent with a role in cheese making and novel endoglucanases associated with degradation of plant material. Similar gene retention was observed in three other distantly related yeasts representative of this ecologically diverse subphylum. The phenomenon thus appears to be widespread in the Saccharomycotina and argues that, alongside neo-functionalization following gene duplication and HGT, specific gene retention must be recognized as an important mechanism for generation of biodiversity and adaptation in yeasts.

Substrate specificity and regioselectivity of fungal AA9 lytic polysaccharide monooxygenases secreted by Podospora anserina

BACKGROUND

The understanding of enzymatic polysaccharide degradation has progressed intensely in the past few years with the identification of a new class of fungal-secreted enzymes, the lytic polysaccharide monooxygenases (LPMOs) that enhance cellulose conversion. In the fungal kingdom, saprotrophic fungi display a high number of genes encoding LPMOs from family AA9 but the functional relevance of this redundancy is not fully understood.

RESULTS

In this study, we investigated a set of AA9 LPMOs identified in the secretomes of the coprophilous ascomycete Podospora anserina, a biomass degrader of recalcitrant substrates. Their activity was assayed on cellulose in synergy with the cellobiose dehydrogenase from the same organism. We showed that the total release of oxidized oligosaccharides from cellulose was higher for PaLPMO9A, PaLPMO9E, and PaLPMO9H that harbored a carbohydrate-binding module from the family CBM1. Investigation of their regioselective mode of action revealed that PaLPMO9A and PaLPMO9H oxidatively cleaved at both C1 and C4 positions while PaLPMO9E released only C1-oxidized products. Rapid cleavage of cellulose was observed using PaLPMO9H that was the most versatile in terms of substrate specificity as it also displayed activity on cello-oligosaccharides and β-(1,4)-linked hemicellulose polysaccharides (e.g., xyloglucan, glucomannan).

CONCLUSIONS

This study provides insights into the mode of cleavage and substrate specificities of fungal AA9 LPMOs that will facilitate their application for the development of future biorefineries.

Recombinant production and characterization of full-length and truncated β-1,3-glucanase PglA from Paenibacillus sp. S09

Background

β-1,3-Glucanases catalyze the hydrolysis of glucan polymers containing β-1,3-linkages. These enzymes are of great biotechnological, agricultural and industrial interest. The applications of β-1,3-glucanases is well established in fungal disease biocontrol, yeast extract production and wine extract clarification. Thus, the identification and characterization of novel β-1,3-glucanases with high catalytic efficiency and stability is of particular interest.

Results

A β-1,3-glucanase gene designated PglA was cloned from a newly isolated strain Paenibacillus sp. S09. The gene PglA contained a 2631-bp open reading frame encoding a polypeptide of 876 amino acids which shows 76% identity with the β-1,3-glucanase (BglH) from Bacillus circulans IAM1165. The encoded protein PglA is composed of a signal peptide, an N-terminal leader region, a glycoside hydrolase family 16 (GH16) catalytic domain and a C-terminal immunoglobulin like (Ig-like) domain. The Escherichia coli expression system of PglA and five truncated derivatives containing one or two modules was constructed to investigate the role of catalytic and non-catalytic modules. The pH for optimal activity of the enzymes was slightly affected (pH 5.5-6.5) by the presence of different modules. However, the temperature for optimal activity was strongly influenced by the C-terminal domain and ranged from 50 to 60°C. Deletion of C-terminal domain resulted in obviously enhancing enzymatic thermostability. Specific activity assay indicated that PglA specifically hydrolyzes β-1,3-glucan. Insoluble β-1,3-glucan binding and hydrolysis were boosted by the presence of N-and C-terminal domains. Kinetic analysis showed that the presence of N-and C-terminus enhances the substrate affinity and catalytic efficiency of the catalytic domain toward laminarin. Carbohydrate-binding assay directly confirmed the binding capabilities of the N-and C-terminal domains.

Conclusions

This study provides new insight into the impacts of non-catalytic modules on enzymatic properties of β-1,3-glucanase. Activity comparison of full-length PglA and truncated forms revealed the negative effect of C-terminal region on thermal stability of the enzyme. Both the N-and C-terminal domains exerted strong binding activity toward insoluble β-1,3-glucan, and could be classified into CBM families.

Processivity and enzymatic mode of a glycoside hydrolase family 5 endoglucanase from Volvariella volvacea

EG1 is a modular glycoside hydrolase family 5 endoglucanase from Volvariella volvacea consisting of an N-terminal carbohydrate-binding module (CBM1) and a catalytic domain (CD). The ratios of soluble to insoluble reducing sugar produced from filter paper after 8 and 24 h of exposure to EG1 were 6.66 and 8.56, respectively, suggesting that it is a processive endoglucanase. Three derivatives of EG1 containing a core domain only or additional CBMs were constructed in order to evaluate the contribution of the CBM to the processivity and enzymatic mode of EG1 under stationary and agitated conditions. All four enzymatic forms exhibited the same mode of action on both soluble and insoluble cellulosic substrates with cellobiose as a main end product. An additional CBM fused at either the N or C terminus reduced specific activity toward soluble and insoluble celluloses under stationary reaction conditions. Deletion of the CBM significantly decreased enzyme processivity. Insertion of an additional CBM also resulted in a dramatic decrease in processivity in enzyme-substrate reaction mixtures incubated for 0.5 h, but this effect was reversed when reactions were allowed to proceed for longer periods (24 h). Further significant differences were observed in the substrate adsorption/desorption patterns of EG1 and enzyme derivatives equipped with an additional CBM under agitated reaction conditions. An additional family 1 CBM improved EG1 processivity on insoluble cellulose under highly agitated conditions. Our data indicate a strong link between high adsorption levels and low desorption levels in the processivity of EG1 and possibly other processive endoglucanses.